<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2023 Workiva-->
<!--r:7508de12-69a9-4818-9ec7-00b38a2cb3e7,g:60b4642b-da77-4b86-962d-2e89e6dd7ade-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:roleRef roleURI="http://www.iconplc.com/role/CONSOLIDATEDBALANCESHEETS" xlink:type="simple" xlink:href="iclr-20221231.xsd#CONSOLIDATEDBALANCESHEETS"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/CONSOLIDATEDBALANCESHEETS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_e8d24034-221c-44f4-99ee-80a1200bbaab" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Liabilities"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_097d93a0-b6cd-4e3d-87cf-b994640ae8d7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_e8d24034-221c-44f4-99ee-80a1200bbaab" xlink:to="loc_us-gaap_LiabilitiesCurrent_097d93a0-b6cd-4e3d-87cf-b994640ae8d7" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermLineOfCredit_1100669c-8572-4ae6-a619-28110f0e22f1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermLineOfCredit"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_e8d24034-221c-44f4-99ee-80a1200bbaab" xlink:to="loc_us-gaap_LongTermLineOfCredit_1100669c-8572-4ae6-a619-28110f0e22f1" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_8f2a92c1-00a5-4b0d-a24f-95dee3f85d55" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_e8d24034-221c-44f4-99ee-80a1200bbaab" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_8f2a92c1-00a5-4b0d-a24f-95dee3f85d55" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_858e37f3-add6-4b83-b805-668cfa94b414" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_e8d24034-221c-44f4-99ee-80a1200bbaab" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_858e37f3-add6-4b83-b805-668cfa94b414" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedIncomeTaxesNoncurrent_ab81c4d6-0865-4fdd-9cd4-b8e43869cafc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedIncomeTaxesNoncurrent"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_e8d24034-221c-44f4-99ee-80a1200bbaab" xlink:to="loc_us-gaap_AccruedIncomeTaxesNoncurrent_ab81c4d6-0865-4fdd-9cd4-b8e43869cafc" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_fd00727c-3dcc-4288-ab26-8346dbb83fca" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:calculationArc order="6" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_e8d24034-221c-44f4-99ee-80a1200bbaab" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_fd00727c-3dcc-4288-ab26-8346dbb83fca" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_188cbcf8-8a93-4f62-989c-e161de2f429d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:calculationArc order="7" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_e8d24034-221c-44f4-99ee-80a1200bbaab" xlink:to="loc_us-gaap_CommitmentsAndContingencies_188cbcf8-8a93-4f62-989c-e161de2f429d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_57994fe4-8b68-48a9-abb5-b6964a229b9a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_d0f46224-3c8e-45a5-933b-716543b5db6b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Liabilities"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquity_57994fe4-8b68-48a9-abb5-b6964a229b9a" xlink:to="loc_us-gaap_Liabilities_d0f46224-3c8e-45a5-933b-716543b5db6b" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_7fc9b487-c183-48be-a394-11ffd1f4a32d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquity_57994fe4-8b68-48a9-abb5-b6964a229b9a" xlink:to="loc_us-gaap_StockholdersEquity_7fc9b487-c183-48be-a394-11ffd1f4a32d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_10b3d1b4-5664-490b-9e7a-eeb889e161e6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsCurrent"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_12717296-2d60-4e3a-954b-c0c9b33e2ba9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_10b3d1b4-5664-490b-9e7a-eeb889e161e6" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_12717296-2d60-4e3a-954b-c0c9b33e2ba9" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_3309b18e-902b-4bcf-8a38-6aaf528cc4e5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_10b3d1b4-5664-490b-9e7a-eeb889e161e6" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_3309b18e-902b-4bcf-8a38-6aaf528cc4e5" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_4ee43b77-9079-44d8-af1c-7046d1f0a64e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_10b3d1b4-5664-490b-9e7a-eeb889e161e6" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_4ee43b77-9079-44d8-af1c-7046d1f0a64e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetGrossCurrent_23626689-0236-4be7-bd19-648fe05a83ed" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractWithCustomerAssetGrossCurrent"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_10b3d1b4-5664-490b-9e7a-eeb889e161e6" xlink:to="loc_us-gaap_ContractWithCustomerAssetGrossCurrent_23626689-0236-4be7-bd19-648fe05a83ed" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NontradeReceivablesCurrent_d3533d16-24c6-442c-ab02-9b27fd669323" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NontradeReceivablesCurrent"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_10b3d1b4-5664-490b-9e7a-eeb889e161e6" xlink:to="loc_us-gaap_NontradeReceivablesCurrent_d3533d16-24c6-442c-ab02-9b27fd669323" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_cc1b9cf1-b3ef-4a67-9129-e2bfa641e0cc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:calculationArc order="6" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_10b3d1b4-5664-490b-9e7a-eeb889e161e6" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_cc1b9cf1-b3ef-4a67-9129-e2bfa641e0cc" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesReceivable_f32e22c4-23de-4c14-af2b-fa14918ac4e3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxesReceivable"/>
    <link:calculationArc order="7" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_10b3d1b4-5664-490b-9e7a-eeb889e161e6" xlink:to="loc_us-gaap_IncomeTaxesReceivable_f32e22c4-23de-4c14-af2b-fa14918ac4e3" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_03e3a5d5-dede-4ea0-8160-aecfc4754b66" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_393df3d6-28d6-456b-a4e7-8f8f4ef4bdf5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockValue"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_03e3a5d5-dede-4ea0-8160-aecfc4754b66" xlink:to="loc_us-gaap_CommonStockValue_393df3d6-28d6-456b-a4e7-8f8f4ef4bdf5" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_9c066504-4b1c-4a36-988f-199fc0bd044b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_03e3a5d5-dede-4ea0-8160-aecfc4754b66" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_9c066504-4b1c-4a36-988f-199fc0bd044b" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_OtherUndenominatedCapital_955f8f5e-08d1-4f7b-8964-b4595c948902" xlink:href="iclr-20221231.xsd#iclr_OtherUndenominatedCapital"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_03e3a5d5-dede-4ea0-8160-aecfc4754b66" xlink:to="loc_iclr_OtherUndenominatedCapital_955f8f5e-08d1-4f7b-8964-b4595c948902" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_000358c7-0827-43ae-b607-41ebaaf1f57b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_03e3a5d5-dede-4ea0-8160-aecfc4754b66" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_000358c7-0827-43ae-b607-41ebaaf1f57b" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_3048b985-c3ce-4a44-988c-f5d08cbdde35" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_03e3a5d5-dede-4ea0-8160-aecfc4754b66" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_3048b985-c3ce-4a44-988c-f5d08cbdde35" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_699f9025-be8d-4ade-afd9-17fe7369b809" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_049c00a1-6865-4df8-ba4e-9b4cabd5d225" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesCurrent_699f9025-be8d-4ade-afd9-17fe7369b809" xlink:to="loc_us-gaap_AccountsPayableCurrent_049c00a1-6865-4df8-ba4e-9b4cabd5d225" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_7585dcb6-1fcc-47cd-b6c3-efbb17632f2e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesCurrent_699f9025-be8d-4ade-afd9-17fe7369b809" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_7585dcb6-1fcc-47cd-b6c3-efbb17632f2e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_39f468fe-3d66-4bf7-a271-4b0110e275f4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesCurrent_699f9025-be8d-4ade-afd9-17fe7369b809" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_39f468fe-3d66-4bf7-a271-4b0110e275f4" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedIncomeTaxesCurrent_44b46ee3-2844-40f6-aeef-5932e7a2cf0d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedIncomeTaxesCurrent"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesCurrent_699f9025-be8d-4ade-afd9-17fe7369b809" xlink:to="loc_us-gaap_AccruedIncomeTaxesCurrent_44b46ee3-2844-40f6-aeef-5932e7a2cf0d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LinesOfCreditCurrent_d7ee55eb-a449-4ee8-b1c6-ef131b51fcc5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LinesOfCreditCurrent"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesCurrent_699f9025-be8d-4ade-afd9-17fe7369b809" xlink:to="loc_us-gaap_LinesOfCreditCurrent_d7ee55eb-a449-4ee8-b1c6-ef131b51fcc5" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_bd4de073-b2b2-4d49-ad2b-90c83eccc556" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Assets"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_75092829-af08-4319-855c-3de42266fb33" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_bd4de073-b2b2-4d49-ad2b-90c83eccc556" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_75092829-af08-4319-855c-3de42266fb33" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_68a4da82-6d3e-4f0a-a555-7eac50a232ac" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_bd4de073-b2b2-4d49-ad2b-90c83eccc556" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_68a4da82-6d3e-4f0a-a555-7eac50a232ac" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_2d68cec1-ea28-4bf1-a123-2fefd3c378cf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityMethodInvestments"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_bd4de073-b2b2-4d49-ad2b-90c83eccc556" xlink:to="loc_us-gaap_EquityMethodInvestments_2d68cec1-ea28-4bf1-a123-2fefd3c378cf" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesReceivableNoncurrent_58b9d85a-22de-44ee-b5bd-ac427f2f7b5e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxesReceivableNoncurrent"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_bd4de073-b2b2-4d49-ad2b-90c83eccc556" xlink:to="loc_us-gaap_IncomeTaxesReceivableNoncurrent_58b9d85a-22de-44ee-b5bd-ac427f2f7b5e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_3cae0b59-6d00-4e02-8bf4-2b153e537ec9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_bd4de073-b2b2-4d49-ad2b-90c83eccc556" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_3cae0b59-6d00-4e02-8bf4-2b153e537ec9" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_3c11d87c-5864-4f4e-b108-3213558d0741" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:calculationArc order="6" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_bd4de073-b2b2-4d49-ad2b-90c83eccc556" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_3c11d87c-5864-4f4e-b108-3213558d0741" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLongTermInvestments_c1349dc4-1182-41bb-8278-a7dbbcc628bf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherLongTermInvestments"/>
    <link:calculationArc order="7" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_bd4de073-b2b2-4d49-ad2b-90c83eccc556" xlink:to="loc_us-gaap_OtherLongTermInvestments_c1349dc4-1182-41bb-8278-a7dbbcc628bf" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_8be25e12-e7a5-4ddc-b34e-807a23b1ceb6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsCurrent"/>
    <link:calculationArc order="8" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_bd4de073-b2b2-4d49-ad2b-90c83eccc556" xlink:to="loc_us-gaap_AssetsCurrent_8be25e12-e7a5-4ddc-b34e-807a23b1ceb6" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxAssetsNet_85bf915f-5bc8-447d-9610-05f99cd54b28" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredIncomeTaxAssetsNet"/>
    <link:calculationArc order="9" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_bd4de073-b2b2-4d49-ad2b-90c83eccc556" xlink:to="loc_us-gaap_DeferredIncomeTaxAssetsNet_85bf915f-5bc8-447d-9610-05f99cd54b28" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_660ed57d-6f4e-41d0-b2e6-44f061c94eb3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill"/>
    <link:calculationArc order="10" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_bd4de073-b2b2-4d49-ad2b-90c83eccc556" xlink:to="loc_us-gaap_Goodwill_660ed57d-6f4e-41d0-b2e6-44f061c94eb3" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/CONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="simple" xlink:href="iclr-20221231.xsd#CONSOLIDATEDSTATEMENTSOFOPERATIONS"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/CONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_1dfa3dc2-c775-435d-92b6-db86b27fb7bc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostsAndExpenses"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCosts_7a95c0c0-d6b6-47aa-99bf-be40109aa458" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestructuringCosts"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_CostsAndExpenses_1dfa3dc2-c775-435d-92b6-db86b27fb7bc" xlink:to="loc_us-gaap_RestructuringCosts_7a95c0c0-d6b6-47aa-99bf-be40109aa458" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_257a505b-6e46-4a04-9a0e-4ec492423be7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_CostsAndExpenses_1dfa3dc2-c775-435d-92b6-db86b27fb7bc" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_257a505b-6e46-4a04-9a0e-4ec492423be7" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_696a954f-ceac-4081-8a38-8eee23e004d1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_CostsAndExpenses_1dfa3dc2-c775-435d-92b6-db86b27fb7bc" xlink:to="loc_us-gaap_DepreciationAndAmortization_696a954f-ceac-4081-8a38-8eee23e004d1" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_c2b04b97-e34d-4a0b-bf00-a76c6e832737" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_CostsAndExpenses_1dfa3dc2-c775-435d-92b6-db86b27fb7bc" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_c2b04b97-e34d-4a0b-bf00-a76c6e832737" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_BusinessCombinationIntegrationRelatedCostsCredits_b71f745d-1610-4d9e-9635-7638bb7656e0" xlink:href="iclr-20221231.xsd#iclr_BusinessCombinationIntegrationRelatedCostsCredits"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_CostsAndExpenses_1dfa3dc2-c775-435d-92b6-db86b27fb7bc" xlink:to="loc_iclr_BusinessCombinationIntegrationRelatedCostsCredits_b71f745d-1610-4d9e-9635-7638bb7656e0" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossIncludingPortionAttributableToNoncontrollingInterest_0794440c-e189-4143-8f89-b2a7670d05a6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeLossIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_7cf2298c-dd71-493b-b6b8-eabf19598454" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeLossIncludingPortionAttributableToNoncontrollingInterest_0794440c-e189-4143-8f89-b2a7670d05a6" xlink:to="loc_us-gaap_OperatingIncomeLoss_7cf2298c-dd71-493b-b6b8-eabf19598454" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInterest_7d89baf3-9291-4440-bcda-9889d532d408" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentIncomeInterest"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeLossIncludingPortionAttributableToNoncontrollingInterest_0794440c-e189-4143-8f89-b2a7670d05a6" xlink:to="loc_us-gaap_InvestmentIncomeInterest_7d89baf3-9291-4440-bcda-9889d532d408" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_0a1fa901-73d7-47a5-b312-3f05fd5de3e2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestExpense"/>
    <link:calculationArc order="3" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeLossIncludingPortionAttributableToNoncontrollingInterest_0794440c-e189-4143-8f89-b2a7670d05a6" xlink:to="loc_us-gaap_InterestExpense_0a1fa901-73d7-47a5-b312-3f05fd5de3e2" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_7eab4a44-1cdb-4754-8a2e-9f922677e4c9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProfitLoss"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_9231bb65-692e-49a4-92bb-6bee6e45ed66" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_ProfitLoss_7eab4a44-1cdb-4754-8a2e-9f922677e4c9" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_9231bb65-692e-49a4-92bb-6bee6e45ed66" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_IncomeLossFromContinuingOperationsBeforeEquityMethodInvestmentsNoncontrollingInterest_c6012934-8aac-44f6-8b35-809c4f120234" xlink:href="iclr-20221231.xsd#iclr_IncomeLossFromContinuingOperationsBeforeEquityMethodInvestmentsNoncontrollingInterest"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_ProfitLoss_7eab4a44-1cdb-4754-8a2e-9f922677e4c9" xlink:to="loc_iclr_IncomeLossFromContinuingOperationsBeforeEquityMethodInvestmentsNoncontrollingInterest_c6012934-8aac-44f6-8b35-809c4f120234" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_IncomeLossFromContinuingOperationsBeforeEquityMethodInvestmentsNoncontrollingInterest_897e6b5c-747d-4e88-9850-40a478c80834" xlink:href="iclr-20221231.xsd#iclr_IncomeLossFromContinuingOperationsBeforeEquityMethodInvestmentsNoncontrollingInterest"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossIncludingPortionAttributableToNoncontrollingInterest_56fb6ff4-bae9-499e-9f18-f41d049c713c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeLossIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_iclr_IncomeLossFromContinuingOperationsBeforeEquityMethodInvestmentsNoncontrollingInterest_897e6b5c-747d-4e88-9850-40a478c80834" xlink:to="loc_us-gaap_IncomeLossIncludingPortionAttributableToNoncontrollingInterest_56fb6ff4-bae9-499e-9f18-f41d049c713c" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_db4d1522-af47-4e6d-89fa-ceff1c7907bc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_iclr_IncomeLossFromContinuingOperationsBeforeEquityMethodInvestmentsNoncontrollingInterest_897e6b5c-747d-4e88-9850-40a478c80834" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_db4d1522-af47-4e6d-89fa-ceff1c7907bc" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_6bb69de1-25df-4d65-bd44-7b6ee723411f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLoss"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_e1d9795e-f861-44b5-b97d-72df36ccded9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProfitLoss"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetIncomeLoss_6bb69de1-25df-4d65-bd44-7b6ee723411f" xlink:to="loc_us-gaap_ProfitLoss_e1d9795e-f861-44b5-b97d-72df36ccded9" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_d41848fc-1371-4839-a1a0-468d5838c212" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetIncomeLoss_6bb69de1-25df-4d65-bd44-7b6ee723411f" xlink:to="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_d41848fc-1371-4839-a1a0-468d5838c212" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_c78aeea5-6fd5-4fdb-bff6-a7e25cb69c8f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_f9b4b497-c236-463a-9812-4bc9611c0511" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostsAndExpenses"/>
    <link:calculationArc order="1" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingIncomeLoss_c78aeea5-6fd5-4fdb-bff6-a7e25cb69c8f" xlink:to="loc_us-gaap_CostsAndExpenses_f9b4b497-c236-463a-9812-4bc9611c0511" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_8a898c01-51d6-4ef0-ba0e-fda9eacb7114" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingIncomeLoss_c78aeea5-6fd5-4fdb-bff6-a7e25cb69c8f" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_8a898c01-51d6-4ef0-ba0e-fda9eacb7114" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/CONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOME" xlink:type="simple" xlink:href="iclr-20221231.xsd#CONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOME"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/CONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOME" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_64165c64-ef70-460e-b16c-b6d5004c9beb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_93771995-cec6-456b-bc95-0638d02fe419" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_64165c64-ef70-460e-b16c-b6d5004c9beb" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_93771995-cec6-456b-bc95-0638d02fe419" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax_649e84d5-d2cb-4a0e-91b2-0b87e40e5d6e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_64165c64-ef70-460e-b16c-b6d5004c9beb" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax_649e84d5-d2cb-4a0e-91b2-0b87e40e5d6e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_65bafd62-9158-43af-ab5a-4151f2201f4a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProfitLoss"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_64165c64-ef70-460e-b16c-b6d5004c9beb" xlink:to="loc_us-gaap_ProfitLoss_65bafd62-9158-43af-ab5a-4151f2201f4a" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_7f160c42-d53d-4135-9b4f-96cff9c16982" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_64165c64-ef70-460e-b16c-b6d5004c9beb" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_7f160c42-d53d-4135-9b4f-96cff9c16982" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_f0d2a825-d185-45d3-aae5-ad69a9bd96cc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_64165c64-ef70-460e-b16c-b6d5004c9beb" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAfterTax_f0d2a825-d185-45d3-aae5-ad69a9bd96cc" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_039ea4d1-02ca-4a9e-9d5a-2557b02b287a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:calculationArc order="6" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_64165c64-ef70-460e-b16c-b6d5004c9beb" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_039ea4d1-02ca-4a9e-9d5a-2557b02b287a" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_0cdc2a33-270c-4c05-8d0b-7943548cf3da" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_9f597a00-a3a5-4cde-ad6a-8276543424d1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTax_0cdc2a33-270c-4c05-8d0b-7943548cf3da" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_9f597a00-a3a5-4cde-ad6a-8276543424d1" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest_72de756c-e841-4f8a-972a-0e01bb8cddc5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTax_0cdc2a33-270c-4c05-8d0b-7943548cf3da" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest_72de756c-e841-4f8a-972a-0e01bb8cddc5" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/CONSOLIDATEDSTATEMENTSOFCASHFLOWS" xlink:type="simple" xlink:href="iclr-20221231.xsd#CONSOLIDATEDSTATEMENTSOFCASHFLOWS"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/CONSOLIDATEDSTATEMENTSOFCASHFLOWS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_5fefd094-3716-4a6a-96b8-9b9363c6cb70" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromStockOptionsExercised_3d84d52f-a8f5-4df3-bc98-f2fd212e565b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromStockOptionsExercised"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_5fefd094-3716-4a6a-96b8-9b9363c6cb70" xlink:to="loc_us-gaap_ProceedsFromStockOptionsExercised_3d84d52f-a8f5-4df3-bc98-f2fd212e565b" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfFinancingCosts_280a656a-dabf-46f0-85f1-0a488e7bf2db" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsOfFinancingCosts"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_5fefd094-3716-4a6a-96b8-9b9363c6cb70" xlink:to="loc_us-gaap_PaymentsOfFinancingCosts_280a656a-dabf-46f0-85f1-0a488e7bf2db" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_34ad090f-bc73-4530-8183-b10e8b645c82" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_5fefd094-3716-4a6a-96b8-9b9363c6cb70" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_34ad090f-bc73-4530-8183-b10e8b645c82" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToMinorityShareholders_a362f2dd-aee0-4472-a4f0-29ae02b3a485" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToMinorityShareholders"/>
    <link:calculationArc order="4" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_5fefd094-3716-4a6a-96b8-9b9363c6cb70" xlink:to="loc_us-gaap_PaymentsToMinorityShareholders_a362f2dd-aee0-4472-a4f0-29ae02b3a485" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForHedgeFinancingActivities_166b014a-6c57-4ae9-92fa-5db55fc0611d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsForHedgeFinancingActivities"/>
    <link:calculationArc order="5" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_5fefd094-3716-4a6a-96b8-9b9363c6cb70" xlink:to="loc_us-gaap_PaymentsForHedgeFinancingActivities_166b014a-6c57-4ae9-92fa-5db55fc0611d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_2050ab31-41fd-4f70-b05d-7b2eb271f512" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock"/>
    <link:calculationArc order="6" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_5fefd094-3716-4a6a-96b8-9b9363c6cb70" xlink:to="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_2050ab31-41fd-4f70-b05d-7b2eb271f512" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_573d546d-a15b-4acc-a87c-2dc1d3a100a4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:calculationArc order="7" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_5fefd094-3716-4a6a-96b8-9b9363c6cb70" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_573d546d-a15b-4acc-a87c-2dc1d3a100a4" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_PaymentsForShareRepurchaseCosts_a9be5909-50c7-4e3e-bfeb-dbc195e4bf9c" xlink:href="iclr-20221231.xsd#iclr_PaymentsForShareRepurchaseCosts"/>
    <link:calculationArc order="8" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_5fefd094-3716-4a6a-96b8-9b9363c6cb70" xlink:to="loc_iclr_PaymentsForShareRepurchaseCosts_a9be5909-50c7-4e3e-bfeb-dbc195e4bf9c" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_42ae81d6-4685-487d-bc41-f28b15127368" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RepaymentsOfLinesOfCredit"/>
    <link:calculationArc order="9" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_5fefd094-3716-4a6a-96b8-9b9363c6cb70" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_42ae81d6-4685-487d-bc41-f28b15127368" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_592d7255-0461-445f-ba92-157556bfccc3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_1aafe8f3-273b-4baf-a7c4-ad6c0ae74c79" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_592d7255-0461-445f-ba92-157556bfccc3" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_1aafe8f3-273b-4baf-a7c4-ad6c0ae74c79" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_52e6009c-397f-4f96-af0e-92a0f94cb791" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_592d7255-0461-445f-ba92-157556bfccc3" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_52e6009c-397f-4f96-af0e-92a0f94cb791" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_6052c1ab-e97e-4284-aae7-4ed71d9fd93d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_592d7255-0461-445f-ba92-157556bfccc3" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_6052c1ab-e97e-4284-aae7-4ed71d9fd93d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_826735af-405d-4ce9-9e61-430a0733ffe9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_592d7255-0461-445f-ba92-157556bfccc3" xlink:to="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_826735af-405d-4ce9-9e61-430a0733ffe9" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_5e90a0bf-9b98-49da-aa81-19234ca47d9d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_6a00de2f-96ab-4f55-97fb-f4e8e534e506" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_5e90a0bf-9b98-49da-aa81-19234ca47d9d" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_6a00de2f-96ab-4f55-97fb-f4e8e534e506" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_7cf8f883-dcab-4446-b94e-9899c1f203de" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_5e90a0bf-9b98-49da-aa81-19234ca47d9d" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_7cf8f883-dcab-4446-b94e-9899c1f203de" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_e12ed61d-624b-4fd4-8549-4b53d6f3c732" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInContractWithCustomerLiability"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_5e90a0bf-9b98-49da-aa81-19234ca47d9d" xlink:to="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_e12ed61d-624b-4fd4-8549-4b53d6f3c732" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxesAndTaxCredits_e37cea62-fa4d-4ea0-b0db-df103dab11d4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredIncomeTaxesAndTaxCredits"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_5e90a0bf-9b98-49da-aa81-19234ca47d9d" xlink:to="loc_us-gaap_DeferredIncomeTaxesAndTaxCredits_e37cea62-fa4d-4ea0-b0db-df103dab11d4" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_218c3f17-f9b8-4bc8-86d6-807ff2d24bdd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable"/>
    <link:calculationArc order="5" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_5e90a0bf-9b98-49da-aa81-19234ca47d9d" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_218c3f17-f9b8-4bc8-86d6-807ff2d24bdd" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_2d79e1af-b0f9-4bd1-96aa-84b7624dc4e6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProfitLoss"/>
    <link:calculationArc order="6" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_5e90a0bf-9b98-49da-aa81-19234ca47d9d" xlink:to="loc_us-gaap_ProfitLoss_2d79e1af-b0f9-4bd1-96aa-84b7624dc4e6" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_f65d242b-4ccd-4d80-9476-46a390242ff6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShareBasedCompensation"/>
    <link:calculationArc order="7" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_5e90a0bf-9b98-49da-aa81-19234ca47d9d" xlink:to="loc_us-gaap_ShareBasedCompensation_f65d242b-4ccd-4d80-9476-46a390242ff6" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_527310f2-623b-4d35-aced-5e1e30d14ec5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ImpairmentOfLongLivedAssetsHeldForUse"/>
    <link:calculationArc order="8" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_5e90a0bf-9b98-49da-aa81-19234ca47d9d" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_527310f2-623b-4d35-aced-5e1e30d14ec5" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense_a4a4ade7-9d36-4b85-9147-c2fad7767ef7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense"/>
    <link:calculationArc order="9" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_5e90a0bf-9b98-49da-aa81-19234ca47d9d" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense_a4a4ade7-9d36-4b85-9147-c2fad7767ef7" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyTransactionGainLossUnrealized_2fc9a764-0b0a-4911-bf8c-2f9a75706bfc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ForeignCurrencyTransactionGainLossUnrealized"/>
    <link:calculationArc order="10" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_5e90a0bf-9b98-49da-aa81-19234ca47d9d" xlink:to="loc_us-gaap_ForeignCurrencyTransactionGainLossUnrealized_2fc9a764-0b0a-4911-bf8c-2f9a75706bfc" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_0d57c7bc-bad8-4dc3-8237-6747223cebbb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:calculationArc order="11" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_5e90a0bf-9b98-49da-aa81-19234ca47d9d" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_0d57c7bc-bad8-4dc3-8237-6747223cebbb" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInContractWithCustomerAsset_230dc0b2-1543-4d27-a60d-83a605b7cbb8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInContractWithCustomerAsset"/>
    <link:calculationArc order="12" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_5e90a0bf-9b98-49da-aa81-19234ca47d9d" xlink:to="loc_us-gaap_IncreaseDecreaseInContractWithCustomerAsset_230dc0b2-1543-4d27-a60d-83a605b7cbb8" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_ef3a94a8-008a-4730-9d90-23a568a2dce2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:calculationArc order="13" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_5e90a0bf-9b98-49da-aa81-19234ca47d9d" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_ef3a94a8-008a-4730-9d90-23a568a2dce2" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherCurrentLiabilities_c9e82ef0-f632-4863-8aa5-ed1c2448c775" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncreaseDecreaseInOtherCurrentLiabilities"/>
    <link:calculationArc order="14" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_5e90a0bf-9b98-49da-aa81-19234ca47d9d" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherCurrentLiabilities_c9e82ef0-f632-4863-8aa5-ed1c2448c775" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNoncashIncomeExpense_b9db17e5-e40f-47cf-96ff-057429a41abd" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherNoncashIncomeExpense"/>
    <link:calculationArc order="15" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_5e90a0bf-9b98-49da-aa81-19234ca47d9d" xlink:to="loc_us-gaap_OtherNoncashIncomeExpense_b9db17e5-e40f-47cf-96ff-057429a41abd" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_GainLossOnIssuanceOfDebt_6b30eb40-7157-4f6c-90ae-0d7f6c0948e1" xlink:href="iclr-20221231.xsd#iclr_GainLossOnIssuanceOfDebt"/>
    <link:calculationArc order="16" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_5e90a0bf-9b98-49da-aa81-19234ca47d9d" xlink:to="loc_iclr_GainLossOnIssuanceOfDebt_6b30eb40-7157-4f6c-90ae-0d7f6c0948e1" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7ae6b138-a064-4f63-990f-8c20cca0b940" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_f76d5f4c-0538-4e24-9bc3-5f3927aa309e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7ae6b138-a064-4f63-990f-8c20cca0b940" xlink:to="loc_us-gaap_ProceedsFromSaleOfAvailableForSaleSecuritiesDebt_f76d5f4c-0538-4e24-9bc3-5f3927aa309e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt_42ac2501-ba28-4a55-9893-5654c47b95f8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7ae6b138-a064-4f63-990f-8c20cca0b940" xlink:to="loc_us-gaap_PaymentsToAcquireAvailableForSaleSecuritiesDebt_42ac2501-ba28-4a55-9893-5654c47b95f8" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireLongtermInvestments_4af4b673-f9f3-406a-a225-6fcd87016cf5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquireLongtermInvestments"/>
    <link:calculationArc order="3" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7ae6b138-a064-4f63-990f-8c20cca0b940" xlink:to="loc_us-gaap_PaymentsToAcquireLongtermInvestments_4af4b673-f9f3-406a-a225-6fcd87016cf5" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_fb1c89b9-aef9-43c6-bdf1-7ddcd4ff6df7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:calculationArc order="4" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7ae6b138-a064-4f63-990f-8c20cca0b940" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_fb1c89b9-aef9-43c6-bdf1-7ddcd4ff6df7" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_c9cdd805-e4c2-4c99-8932-21f976d9bc6d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:calculationArc order="5" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7ae6b138-a064-4f63-990f-8c20cca0b940" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_c9cdd805-e4c2-4c99-8932-21f976d9bc6d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireEquityMethodInvestments_5b78c559-3ba8-4046-982a-0a76cca87b69" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquireEquityMethodInvestments"/>
    <link:calculationArc order="6" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7ae6b138-a064-4f63-990f-8c20cca0b940" xlink:to="loc_us-gaap_PaymentsToAcquireEquityMethodInvestments_5b78c559-3ba8-4046-982a-0a76cca87b69" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToFundLongtermLoansToRelatedParties_579b7171-4973-4307-9b0b-4d5841706d83" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToFundLongtermLoansToRelatedParties"/>
    <link:calculationArc order="7" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7ae6b138-a064-4f63-990f-8c20cca0b940" xlink:to="loc_us-gaap_PaymentsToFundLongtermLoansToRelatedParties_579b7171-4973-4307-9b0b-4d5841706d83" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfLongtermInvestments_ae06208f-29c4-4211-b05d-40049c0683e3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromSaleOfLongtermInvestments"/>
    <link:calculationArc order="8" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_7ae6b138-a064-4f63-990f-8c20cca0b940" xlink:to="loc_us-gaap_ProceedsFromSaleOfLongtermInvestments_ae06208f-29c4-4211-b05d-40049c0683e3" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/ContractBalancesDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#ContractBalancesDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/ContractBalancesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_iclr_ChangeinAdvancePaymentsNettedAgainstUnbilledContractsReceivable_df8cc902-de12-44be-a98e-0a07fc0a290c" xlink:href="iclr-20221231.xsd#iclr_ChangeinAdvancePaymentsNettedAgainstUnbilledContractsReceivable"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_IncreaseDecreaseInContractwithCustomerAssetGrossCurrent_fc33972d-f44e-4fae-af48-7c00fabe694f" xlink:href="iclr-20221231.xsd#iclr_IncreaseDecreaseInContractwithCustomerAssetGrossCurrent"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_iclr_ChangeinAdvancePaymentsNettedAgainstUnbilledContractsReceivable_df8cc902-de12-44be-a98e-0a07fc0a290c" xlink:to="loc_iclr_IncreaseDecreaseInContractwithCustomerAssetGrossCurrent_fc33972d-f44e-4fae-af48-7c00fabe694f" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_IncreaseDecreaseInContractsWithCustomersLiabilityCurrent_559ba228-0471-4755-b74b-cad7cfebe830" xlink:href="iclr-20221231.xsd#iclr_IncreaseDecreaseInContractsWithCustomersLiabilityCurrent"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_iclr_ChangeinAdvancePaymentsNettedAgainstUnbilledContractsReceivable_df8cc902-de12-44be-a98e-0a07fc0a290c" xlink:to="loc_iclr_IncreaseDecreaseInContractsWithCustomersLiabilityCurrent_559ba228-0471-4755-b74b-cad7cfebe830" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_ContractsReceivableGross_efa1c35f-fd1e-4ab2-bb2f-afe8a343ff0d" xlink:href="iclr-20221231.xsd#iclr_ContractsReceivableGross"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BilledContractReceivables_c24422df-3f9c-4959-a95d-84bd99ac7bf8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BilledContractReceivables"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_iclr_ContractsReceivableGross_efa1c35f-fd1e-4ab2-bb2f-afe8a343ff0d" xlink:to="loc_us-gaap_BilledContractReceivables_c24422df-3f9c-4959-a95d-84bd99ac7bf8" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivable_0f93595f-c003-4f6e-b917-b47987a5dce3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivable"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_iclr_ContractsReceivableGross_efa1c35f-fd1e-4ab2-bb2f-afe8a343ff0d" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivable_0f93595f-c003-4f6e-b917-b47987a5dce3" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_ContractsReceivableNet_347f275f-eab9-4d9e-8c31-d832c978ccb0" xlink:href="iclr-20221231.xsd#iclr_ContractsReceivableNet"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_ContractsReceivableGross_a391114c-3a0b-40d7-bbdb-3b89fa9652ef" xlink:href="iclr-20221231.xsd#iclr_ContractsReceivableGross"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_iclr_ContractsReceivableNet_347f275f-eab9-4d9e-8c31-d832c978ccb0" xlink:to="loc_iclr_ContractsReceivableGross_a391114c-3a0b-40d7-bbdb-3b89fa9652ef" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetGrossCurrent_1366b95c-78eb-43e4-9ba0-af2cf73aab6e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractWithCustomerAssetGrossCurrent"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_iclr_ContractsReceivableNet_347f275f-eab9-4d9e-8c31-d832c978ccb0" xlink:to="loc_us-gaap_ContractWithCustomerAssetGrossCurrent_1366b95c-78eb-43e4-9ba0-af2cf73aab6e" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/BusinessCombinationsFairValueofConsiderationTransferredPRAAcquisitionDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#BusinessCombinationsFairValueofConsiderationTransferredPRAAcquisitionDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/BusinessCombinationsFairValueofConsiderationTransferredPRAAcquisitionDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_1c0a8503-0f0c-4c63-81a5-bb7c49fc8112" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_c661b8d1-b635-44e6-a2a2-d68e481f15c9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferred1_1c0a8503-0f0c-4c63-81a5-bb7c49fc8112" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_c661b8d1-b635-44e6-a2a2-d68e481f15c9" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_b93f5774-8e96-4989-a5f5-4955659f66ab" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferred1_1c0a8503-0f0c-4c63-81a5-bb7c49fc8112" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_b93f5774-8e96-4989-a5f5-4955659f66ab" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_aba18c5c-1307-4ded-b4de-45b7083cad0f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferred1_1c0a8503-0f0c-4c63-81a5-bb7c49fc8112" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_aba18c5c-1307-4ded-b4de-45b7083cad0f" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredOther1_e3a794c8-672e-4c61-a3f9-92bb6217ab97" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationConsiderationTransferredOther1"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferred1_1c0a8503-0f0c-4c63-81a5-bb7c49fc8112" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredOther1_e3a794c8-672e-4c61-a3f9-92bb6217ab97" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/BusinessCombinationsScheduleofAcquisitionsPRAAcquisitionDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#BusinessCombinationsScheduleofAcquisitionsPRAAcquisitionDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/BusinessCombinationsScheduleofAcquisitionsPRAAcquisitionDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_00169318-e2e2-40ed-ba8d-34e3b2f0067c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_c4260f59-6abd-4722-a2d2-b23efb41e062" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities"/>
    <link:calculationArc order="1" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_00169318-e2e2-40ed-ba8d-34e3b2f0067c" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilities_c4260f59-6abd-4722-a2d2-b23efb41e062" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedNoncurrentOperatingLeaseLiability_f4a3c328-31a3-4234-9a4c-fa214f298413" xlink:href="iclr-20221231.xsd#iclr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedNoncurrentOperatingLeaseLiability"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_00169318-e2e2-40ed-ba8d-34e3b2f0067c" xlink:to="loc_iclr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedNoncurrentOperatingLeaseLiability_f4a3c328-31a3-4234-9a4c-fa214f298413" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssets_98978e1e-5307-4358-80c1-d70916b0e6da" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssets"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_00169318-e2e2-40ed-ba8d-34e3b2f0067c" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssets_98978e1e-5307-4358-80c1-d70916b0e6da" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_a1ef1cb9-0c70-4358-b381-cd53f0a7b1f3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_00169318-e2e2-40ed-ba8d-34e3b2f0067c" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_a1ef1cb9-0c70-4358-b381-cd53f0a7b1f3" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_d7c4211c-32dc-4cd3-8b8a-85a90846aa2b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_00169318-e2e2-40ed-ba8d-34e3b2f0067c" xlink:to="loc_us-gaap_Goodwill_d7c4211c-32dc-4cd3-8b8a-85a90846aa2b" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_16ea6c16-6a29-4db9-9a17-3a379fb77c6a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets"/>
    <link:calculationArc order="6" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_00169318-e2e2-40ed-ba8d-34e3b2f0067c" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_16ea6c16-6a29-4db9-9a17-3a379fb77c6a" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAsset_c6918f1a-3a7e-4c38-aeb2-a22dba92a433" xlink:href="iclr-20221231.xsd#iclr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAsset"/>
    <link:calculationArc order="7" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_00169318-e2e2-40ed-ba8d-34e3b2f0067c" xlink:to="loc_iclr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAsset_c6918f1a-3a7e-4c38-aeb2-a22dba92a433" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther_e4c3c1d5-333c-44e6-adf9-9a7b248be97e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther"/>
    <link:calculationArc order="8" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_00169318-e2e2-40ed-ba8d-34e3b2f0067c" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsOther_e4c3c1d5-333c-44e6-adf9-9a7b248be97e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_6b37d5f6-cf2e-4932-9cb8-ad8c17b72977" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles"/>
    <link:calculationArc order="9" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_00169318-e2e2-40ed-ba8d-34e3b2f0067c" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles_6b37d5f6-cf2e-4932-9cb8-ad8c17b72977" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_ecae5657-5de4-44a9-820f-9abee8ed6e0d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable"/>
    <link:calculationArc order="10" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_00169318-e2e2-40ed-ba8d-34e3b2f0067c" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_ecae5657-5de4-44a9-820f-9abee8ed6e0d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_c77891e2-f43f-4132-b2df-9b1644c83d45" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther"/>
    <link:calculationArc order="11" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_00169318-e2e2-40ed-ba8d-34e3b2f0067c" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_c77891e2-f43f-4132-b2df-9b1644c83d45" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther_552a8964-a251-4c27-a4c9-ff0c8e2a2c3e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther"/>
    <link:calculationArc order="12" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_00169318-e2e2-40ed-ba8d-34e3b2f0067c" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther_552a8964-a251-4c27-a4c9-ff0c8e2a2c3e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentOperatingLeaseLiability_2ece2700-b28b-4471-aa4c-7a312a31eeb0" xlink:href="iclr-20221231.xsd#iclr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentOperatingLeaseLiability"/>
    <link:calculationArc order="13" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_00169318-e2e2-40ed-ba8d-34e3b2f0067c" xlink:to="loc_iclr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentOperatingLeaseLiability_2ece2700-b28b-4471-aa4c-7a312a31eeb0" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_cc9ca722-36b1-47ba-9780-c67a9c143725" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:calculationArc order="14" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_00169318-e2e2-40ed-ba8d-34e3b2f0067c" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_cc9ca722-36b1-47ba-9780-c67a9c143725" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_f7c507f3-58c7-4ca5-afa4-323d38c6216e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents"/>
    <link:calculationArc order="15" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_00169318-e2e2-40ed-ba8d-34e3b2f0067c" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_f7c507f3-58c7-4ca5-afa4-323d38c6216e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedContractWithCustomerLiabilityCurrent_fc307350-d96f-42a9-bc22-f614b18fbdf2" xlink:href="iclr-20221231.xsd#iclr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedContractWithCustomerLiabilityCurrent"/>
    <link:calculationArc order="16" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_00169318-e2e2-40ed-ba8d-34e3b2f0067c" xlink:to="loc_iclr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedContractWithCustomerLiabilityCurrent_fc307350-d96f-42a9-bc22-f614b18fbdf2" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/PropertyPlantandEquipmentnetDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#PropertyPlantandEquipmentnetDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/PropertyPlantandEquipmentnetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_49964393-e39b-4771-97e7-d4df950bf1a5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Land_7c37b946-68c7-499f-bcf0-8fda73f9a008" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Land"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentGross_49964393-e39b-4771-97e7-d4df950bf1a5" xlink:to="loc_us-gaap_Land_7c37b946-68c7-499f-bcf0-8fda73f9a008" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BuildingsAndImprovementsGross_c265501f-32f2-4530-ac5d-dcfb395ec50a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BuildingsAndImprovementsGross"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentGross_49964393-e39b-4771-97e7-d4df950bf1a5" xlink:to="loc_us-gaap_BuildingsAndImprovementsGross_c265501f-32f2-4530-ac5d-dcfb395ec50a" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedComputerSoftwareGross_7af89941-aaa9-459f-a81e-8865c5aff1e7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CapitalizedComputerSoftwareGross"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentGross_49964393-e39b-4771-97e7-d4df950bf1a5" xlink:to="loc_us-gaap_CapitalizedComputerSoftwareGross_7af89941-aaa9-459f-a81e-8865c5aff1e7" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesGross_6e7fa2b6-6640-4210-89fe-a4f5c9e79aeb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FurnitureAndFixturesGross"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentGross_49964393-e39b-4771-97e7-d4df950bf1a5" xlink:to="loc_us-gaap_FurnitureAndFixturesGross_6e7fa2b6-6640-4210-89fe-a4f5c9e79aeb" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentGross_182fbca7-7f81-4645-ac41-97abfc98d7fc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MachineryAndEquipmentGross"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentGross_49964393-e39b-4771-97e7-d4df950bf1a5" xlink:to="loc_us-gaap_MachineryAndEquipmentGross_182fbca7-7f81-4645-ac41-97abfc98d7fc" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsGross_5b432675-6149-4be9-9b48-435e9bf40034" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseholdImprovementsGross"/>
    <link:calculationArc order="6" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentGross_49964393-e39b-4771-97e7-d4df950bf1a5" xlink:to="loc_us-gaap_LeaseholdImprovementsGross_5b432675-6149-4be9-9b48-435e9bf40034" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_VehiclesGross_6d59b238-e7f0-4e55-b78c-d6f240e52647" xlink:href="iclr-20221231.xsd#iclr_VehiclesGross"/>
    <link:calculationArc order="7" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentGross_49964393-e39b-4771-97e7-d4df950bf1a5" xlink:to="loc_iclr_VehiclesGross_6d59b238-e7f0-4e55-b78c-d6f240e52647" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_55272bd0-906a-4b3a-a63d-ff615c2d5f89" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_def5bba7-4a72-448b-8436-93baf4926ac7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNet_55272bd0-906a-4b3a-a63d-ff615c2d5f89" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_def5bba7-4a72-448b-8436-93baf4926ac7" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_1fae0959-cab7-47ad-9384-08b3feef390a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentNet_55272bd0-906a-4b3a-a63d-ff615c2d5f89" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_1fae0959-cab7-47ad-9384-08b3feef390a" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/IntangibleAssetsSummaryofIntangibleAssetsDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#IntangibleAssetsSummaryofIntangibleAssetsDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/IntangibleAssetsSummaryofIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_cab0868b-7bcc-450b-88e6-e54bfa69695c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_35f70b4f-7991-4627-a66c-2e5bb8117fd1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNet_cab0868b-7bcc-450b-88e6-e54bfa69695c" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_35f70b4f-7991-4627-a66c-2e5bb8117fd1" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_bcc9271e-3a3c-4454-bb16-f1323cb5f866" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNet_cab0868b-7bcc-450b-88e6-e54bfa69695c" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_bcc9271e-3a3c-4454-bb16-f1323cb5f866" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/IntangibleAssetsFutureIntangibleAssetAmortizationExpenseDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#IntangibleAssetsFutureIntangibleAssetAmortizationExpenseDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/IntangibleAssetsFutureIntangibleAssetAmortizationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_iclr_FiniteLivedIntangibleAssetsAmortizationExpenseNet_e9bc6d5a-c826-4f47-b095-411a062263af" xlink:href="iclr-20221231.xsd#iclr_FiniteLivedIntangibleAssetsAmortizationExpenseNet"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_e4d68f55-508c-4989-bfbf-c0658dd280d1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_iclr_FiniteLivedIntangibleAssetsAmortizationExpenseNet_e9bc6d5a-c826-4f47-b095-411a062263af" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_e4d68f55-508c-4989-bfbf-c0658dd280d1" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_da4d387d-b90e-4fe1-b681-7a6c7d8556c9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_iclr_FiniteLivedIntangibleAssetsAmortizationExpenseNet_e9bc6d5a-c826-4f47-b095-411a062263af" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_da4d387d-b90e-4fe1-b681-7a6c7d8556c9" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_b1a61be4-3993-4907-980f-3df20fbc9b8f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_iclr_FiniteLivedIntangibleAssetsAmortizationExpenseNet_e9bc6d5a-c826-4f47-b095-411a062263af" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_b1a61be4-3993-4907-980f-3df20fbc9b8f" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_f1feda90-a2a0-4a61-ac50-4970860bf41a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_iclr_FiniteLivedIntangibleAssetsAmortizationExpenseNet_e9bc6d5a-c826-4f47-b095-411a062263af" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_f1feda90-a2a0-4a61-ac50-4970860bf41a" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_ed8d82ca-6b17-43e2-b267-300014408997" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_iclr_FiniteLivedIntangibleAssetsAmortizationExpenseNet_e9bc6d5a-c826-4f47-b095-411a062263af" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_ed8d82ca-6b17-43e2-b267-300014408997" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/OtherLiabilitiesDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#OtherLiabilitiesDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/OtherLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_9ff905ff-529e-43c4-a5b0-3716f1af1e75" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherSundryLiabilitiesCurrent_4dddcac5-0ddf-4220-b9c5-fac2adb99648" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherSundryLiabilitiesCurrent"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OtherLiabilitiesCurrent_9ff905ff-529e-43c4-a5b0-3716f1af1e75" xlink:to="loc_us-gaap_OtherSundryLiabilitiesCurrent_4dddcac5-0ddf-4220-b9c5-fac2adb99648" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_e974e54e-1499-4a08-9940-e626ad78a5ee" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrent"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OtherLiabilitiesCurrent_9ff905ff-529e-43c4-a5b0-3716f1af1e75" xlink:to="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_e974e54e-1499-4a08-9940-e626ad78a5ee" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_a035ef47-2f21-409a-86db-b86e70be5b46" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OtherLiabilitiesCurrent_9ff905ff-529e-43c4-a5b0-3716f1af1e75" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_a035ef47-2f21-409a-86db-b86e70be5b46" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedUtilitiesCurrent_56f9a1d8-d82f-4a51-b07c-d1760dd661f7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccruedUtilitiesCurrent"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OtherLiabilitiesCurrent_9ff905ff-529e-43c4-a5b0-3716f1af1e75" xlink:to="loc_us-gaap_AccruedUtilitiesCurrent_56f9a1d8-d82f-4a51-b07c-d1760dd661f7" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesCurrent_d20a103f-fdee-49e5-a23f-b6fad03f0233" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAccruedLiabilitiesCurrent"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OtherLiabilitiesCurrent_9ff905ff-529e-43c4-a5b0-3716f1af1e75" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesCurrent_d20a103f-fdee-49e5-a23f-b6fad03f0233" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_RestructuringReserveandOtherLiabilitiesCurrent_1cb6173c-b06f-4e1e-8e8e-369f5fd03021" xlink:href="iclr-20221231.xsd#iclr_RestructuringReserveandOtherLiabilitiesCurrent"/>
    <link:calculationArc order="6" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OtherLiabilitiesCurrent_9ff905ff-529e-43c4-a5b0-3716f1af1e75" xlink:to="loc_iclr_RestructuringReserveandOtherLiabilitiesCurrent_1cb6173c-b06f-4e1e-8e8e-369f5fd03021" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_CapitalGovernmentGrantsCurrent_bf921e36-38b2-4277-8419-2a52a169f243" xlink:href="iclr-20221231.xsd#iclr_CapitalGovernmentGrantsCurrent"/>
    <link:calculationArc order="7" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OtherLiabilitiesCurrent_9ff905ff-529e-43c4-a5b0-3716f1af1e75" xlink:to="loc_iclr_CapitalGovernmentGrantsCurrent_bf921e36-38b2-4277-8419-2a52a169f243" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/NoncurrentBankCreditLinesandLoanFacilitiesScheduleofLongtermDebtDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#NoncurrentBankCreditLinesandLoanFacilitiesScheduleofLongtermDebtDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/NoncurrentBankCreditLinesandLoanFacilitiesScheduleofLongtermDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_6aa26279-de41-45b8-8a47-75f085e9b923" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_LongTermDebtExcludingCurrentMaturitiesGross_574b6e7b-c291-4a93-b63d-b143f1fea777" xlink:href="iclr-20221231.xsd#iclr_LongTermDebtExcludingCurrentMaturitiesGross"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LongTermDebtNoncurrent_6aa26279-de41-45b8-8a47-75f085e9b923" xlink:to="loc_iclr_LongTermDebtExcludingCurrentMaturitiesGross_574b6e7b-c291-4a93-b63d-b143f1fea777" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_43cbe91f-8392-4c34-a884-35576c3ae2be" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LongTermDebtNoncurrent_6aa26279-de41-45b8-8a47-75f085e9b923" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_43cbe91f-8392-4c34-a884-35576c3ae2be" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/NoncurrentBankCreditLinesandLoanFacilitiesScheduleofFinanceCostDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#NoncurrentBankCreditLinesandLoanFacilitiesScheduleofFinanceCostDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/NoncurrentBankCreditLinesandLoanFacilitiesScheduleofFinanceCostDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_d029e4c3-def2-41e4-b362-2877c8bf625d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestExpense"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_e9949526-c32a-408a-8cc6-9924bbc6023b" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_InterestExpense_d029e4c3-def2-41e4-b362-2877c8bf625d" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_e9949526-c32a-408a-8cc6-9924bbc6023b" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_InterestExpenseCreditOther_da51fcc9-ac76-4620-acc8-292618d69729" xlink:href="iclr-20221231.xsd#iclr_InterestExpenseCreditOther"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_InterestExpense_d029e4c3-def2-41e4-b362-2877c8bf625d" xlink:to="loc_iclr_InterestExpenseCreditOther_da51fcc9-ac76-4620-acc8-292618d69729" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_bb3a6a49-97b7-48bd-998e-3ccd100c8e60" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestExpenseDebt"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_InterestExpense_d029e4c3-def2-41e4-b362-2877c8bf625d" xlink:to="loc_us-gaap_InterestExpenseDebt_bb3a6a49-97b7-48bd-998e-3ccd100c8e60" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_TransactionAndOneTimeFinancingCosts_54b31aab-1686-4414-8b97-f1d364361cef" xlink:href="iclr-20221231.xsd#iclr_TransactionAndOneTimeFinancingCosts"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_InterestExpense_d029e4c3-def2-41e4-b362-2877c8bf625d" xlink:to="loc_iclr_TransactionAndOneTimeFinancingCosts_54b31aab-1686-4414-8b97-f1d364361cef" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/NoncurrentBankCreditLinesandLoanFacilitiesScheduleofMaturitiesofLongtermDebtDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#NoncurrentBankCreditLinesandLoanFacilitiesScheduleofMaturitiesofLongtermDebtDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/NoncurrentBankCreditLinesandLoanFacilitiesScheduleofMaturitiesofLongtermDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_31241163-54e6-4382-8290-18ce1817e9c5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebt"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_6e8c469b-d3d3-4249-8873-b9d0470bae12" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LongTermDebt_31241163-54e6-4382-8290-18ce1817e9c5" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_6e8c469b-d3d3-4249-8873-b9d0470bae12" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_b7204e14-6d72-4db1-b2a6-98980056429d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LongTermDebt_31241163-54e6-4382-8290-18ce1817e9c5" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_b7204e14-6d72-4db1-b2a6-98980056429d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_c981f7c4-f17d-412b-8921-7079ed436f2c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LongTermDebt_31241163-54e6-4382-8290-18ce1817e9c5" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths_c981f7c4-f17d-412b-8921-7079ed436f2c" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_LongTermDebtMaturityYearFiveAndThereafter_c0038aeb-83e1-4367-adb0-a1104ade18a6" xlink:href="iclr-20221231.xsd#iclr_LongTermDebtMaturityYearFiveAndThereafter"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LongTermDebt_31241163-54e6-4382-8290-18ce1817e9c5" xlink:to="loc_iclr_LongTermDebtMaturityYearFiveAndThereafter_c0038aeb-83e1-4367-adb0-a1104ade18a6" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_af490e77-a04b-4638-9e6f-a1b3e1991108" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LongTermDebt_31241163-54e6-4382-8290-18ce1817e9c5" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_af490e77-a04b-4638-9e6f-a1b3e1991108" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/OperatingLeasesLeaseCostsDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#OperatingLeasesLeaseCostsDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/OperatingLeasesLeaseCostsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseCost_3ecef276-2881-4f03-93bc-495a62c41557" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseCost"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubleaseIncome_70324a91-ca72-4aad-b17d-edd192eb9624" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SubleaseIncome"/>
    <link:calculationArc order="1" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LeaseCost_3ecef276-2881-4f03-93bc-495a62c41557" xlink:to="loc_us-gaap_SubleaseIncome_70324a91-ca72-4aad-b17d-edd192eb9624" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseCost_89892f2a-5b46-4346-8f06-45f47a760f60" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseCost"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LeaseCost_3ecef276-2881-4f03-93bc-495a62c41557" xlink:to="loc_us-gaap_OperatingLeaseCost_89892f2a-5b46-4346-8f06-45f47a760f60" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/OperatingLeasesOperatingLeasesOperatingLeaseMaturityDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#OperatingLeasesOperatingLeasesOperatingLeaseMaturityDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/OperatingLeasesOperatingLeasesOperatingLeaseMaturityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_261d9864-8371-483c-9d33-273682bcdef7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_03598d77-2a53-4554-8f53-bab8a080c119" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_261d9864-8371-483c-9d33-273682bcdef7" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount_03598d77-2a53-4554-8f53-bab8a080c119" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiability_e00bca4b-502d-47a9-835a-457222e633a3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingLeaseLiability"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_261d9864-8371-483c-9d33-273682bcdef7" xlink:to="loc_us-gaap_OperatingLeaseLiability_e00bca4b-502d-47a9-835a-457222e633a3" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/OperatingLeasesOperatingLeasesOperatingLeaseMaturityDetails_1" xlink:type="simple" xlink:href="iclr-20221231.xsd#OperatingLeasesOperatingLeasesOperatingLeaseMaturityDetails_1"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/OperatingLeasesOperatingLeasesOperatingLeaseMaturityDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_4af2ba49-0a81-41f1-bc60-796b6166502c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths_c236c163-5d74-48d5-a1d1-d663cf1876e0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_4af2ba49-0a81-41f1-bc60-796b6166502c" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths_c236c163-5d74-48d5-a1d1-d663cf1876e0" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_c9771d61-08f2-4983-97bf-7792ae71f484" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_4af2ba49-0a81-41f1-bc60-796b6166502c" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearTwo_c9771d61-08f2-4983-97bf-7792ae71f484" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_7a1f2bb8-114d-4f93-b26a-d76bf2b84a80" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_4af2ba49-0a81-41f1-bc60-796b6166502c" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearThree_7a1f2bb8-114d-4f93-b26a-d76bf2b84a80" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour_02850966-1de9-40e2-8105-a86a3104b0f2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_4af2ba49-0a81-41f1-bc60-796b6166502c" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFour_02850966-1de9-40e2-8105-a86a3104b0f2" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive_d52da755-2225-4e4a-9028-e2c25cc83a3d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_4af2ba49-0a81-41f1-bc60-796b6166502c" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueYearFive_d52da755-2225-4e4a-9028-e2c25cc83a3d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive_8e178eb7-ebdc-4154-9826-7e2ed9ee3b31" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive"/>
    <link:calculationArc order="6" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue_4af2ba49-0a81-41f1-bc60-796b6166502c" xlink:to="loc_us-gaap_LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive_8e178eb7-ebdc-4154-9826-7e2ed9ee3b31" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/NoncurrentotherliabilitiesDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#NoncurrentotherliabilitiesDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/NoncurrentotherliabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_9251c56c-6362-4741-af20-9a04a644921a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherSundryLiabilitiesNoncurrent_38cd8b48-7d07-4eb3-bde3-cd4f8cb7c231" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherSundryLiabilitiesNoncurrent"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OtherLiabilitiesNoncurrent_9251c56c-6362-4741-af20-9a04a644921a" xlink:to="loc_us-gaap_OtherSundryLiabilitiesNoncurrent_38cd8b48-7d07-4eb3-bde3-cd4f8cb7c231" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPensionPlanLiabilitiesNoncurrent_29eee8cd-d705-4f75-baca-10db863376c1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPensionPlanLiabilitiesNoncurrent"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OtherLiabilitiesNoncurrent_9251c56c-6362-4741-af20-9a04a644921a" xlink:to="loc_us-gaap_DefinedBenefitPensionPlanLiabilitiesNoncurrent_29eee8cd-d705-4f75-baca-10db863376c1" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/IncomeTaxesComponentsofProvisionforIncomeTaxesDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#IncomeTaxesComponentsofProvisionforIncomeTaxesDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/IncomeTaxesComponentsofProvisionforIncomeTaxesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxEffectsAllocatedDirectlyToEquity_4218250d-71f4-4fd4-a05e-b11fe36965e0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxEffectsAllocatedDirectlyToEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_085bbebb-3bd9-4212-8b86-fda7ce88c6a4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeTaxEffectsAllocatedDirectlyToEquity_4218250d-71f4-4fd4-a05e-b11fe36965e0" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_085bbebb-3bd9-4212-8b86-fda7ce88c6a4" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTranslationGainLossArisingDuringPeriodTax_4753c151-569b-4056-8872-add49d42b354" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTranslationGainLossArisingDuringPeriodTax"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeTaxEffectsAllocatedDirectlyToEquity_4218250d-71f4-4fd4-a05e-b11fe36965e0" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTranslationGainLossArisingDuringPeriodTax_4753c151-569b-4056-8872-add49d42b354" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_4cacb348-0d11-4b70-8146-b82b1b54c729" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CurrentIncomeTaxExpenseBenefit_f08121cb-09c2-4ce1-b258-d7678fba7e4c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CurrentIncomeTaxExpenseBenefit"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefit_4cacb348-0d11-4b70-8146-b82b1b54c729" xlink:to="loc_us-gaap_CurrentIncomeTaxExpenseBenefit_f08121cb-09c2-4ce1-b258-d7678fba7e4c" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_90170187-3343-486a-99b4-8b7331596a1f" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefit_4cacb348-0d11-4b70-8146-b82b1b54c729" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_90170187-3343-486a-99b4-8b7331596a1f" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/IncomeTaxesConsolidatedReportedProvisionforIncomeTaxesDifferedfromStatutoryRateDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#IncomeTaxesConsolidatedReportedProvisionforIncomeTaxesDifferedfromStatutoryRateDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/IncomeTaxesConsolidatedReportedProvisionforIncomeTaxesDifferedfromStatutoryRateDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_4729da6a-08dc-468c-b8a1-5b397ae89948" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate_b64d79e8-e1c1-452b-a6d8-4a0f2d122ece" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefit_4729da6a-08dc-468c-b8a1-5b397ae89948" xlink:to="loc_us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate_b64d79e8-e1c1-452b-a6d8-4a0f2d122ece" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationForeignIncomeTaxRateDifferential_2489b715-85d2-4249-80d8-569c9199d3f9" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxReconciliationForeignIncomeTaxRateDifferential"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefit_4729da6a-08dc-468c-b8a1-5b397ae89948" xlink:to="loc_us-gaap_IncomeTaxReconciliationForeignIncomeTaxRateDifferential_2489b715-85d2-4249-80d8-569c9199d3f9" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationTaxCreditsResearch_058354d7-b1dc-4b9a-8e5f-bd3563709810" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxReconciliationTaxCreditsResearch"/>
    <link:calculationArc order="3" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefit_4729da6a-08dc-468c-b8a1-5b397ae89948" xlink:to="loc_us-gaap_IncomeTaxReconciliationTaxCreditsResearch_058354d7-b1dc-4b9a-8e5f-bd3563709810" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance_7141fc66-10d6-444b-afcc-bc8cae7af01a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefit_4729da6a-08dc-468c-b8a1-5b397ae89948" xlink:to="loc_us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance_7141fc66-10d6-444b-afcc-bc8cae7af01a" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationChangeInEnactedTaxRate_17d6b3c4-f33e-4df7-a955-2104746be891" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxReconciliationChangeInEnactedTaxRate"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefit_4729da6a-08dc-468c-b8a1-5b397ae89948" xlink:to="loc_us-gaap_IncomeTaxReconciliationChangeInEnactedTaxRate_17d6b3c4-f33e-4df7-a955-2104746be891" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsPeriodIncreaseDecrease_6382817e-4d9c-40f2-96cb-75705b6e59c1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_UnrecognizedTaxBenefitsPeriodIncreaseDecrease"/>
    <link:calculationArc order="6" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefit_4729da6a-08dc-468c-b8a1-5b397ae89948" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsPeriodIncreaseDecrease_6382817e-4d9c-40f2-96cb-75705b6e59c1" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationOtherReconcilingItems_ee19c589-294c-49bb-b41a-c09d508b9f28" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxReconciliationOtherReconcilingItems"/>
    <link:calculationArc order="7" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefit_4729da6a-08dc-468c-b8a1-5b397ae89948" xlink:to="loc_us-gaap_IncomeTaxReconciliationOtherReconcilingItems_ee19c589-294c-49bb-b41a-c09d508b9f28" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost_80084d8a-68bd-451e-81e7-803c028e8c8e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost"/>
    <link:calculationArc order="8" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefit_4729da6a-08dc-468c-b8a1-5b397ae89948" xlink:to="loc_us-gaap_IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost_80084d8a-68bd-451e-81e7-803c028e8c8e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationNondeductibleExpenseAmortization_e0a0ef43-f2f2-48d1-967a-a3f57e944270" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxReconciliationNondeductibleExpenseAmortization"/>
    <link:calculationArc order="9" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefit_4729da6a-08dc-468c-b8a1-5b397ae89948" xlink:to="loc_us-gaap_IncomeTaxReconciliationNondeductibleExpenseAmortization_e0a0ef43-f2f2-48d1-967a-a3f57e944270" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/IncomeTaxesTaxEffectsofTemporaryDifferencesThatGiveRisetoSignificantPortionsofDeferredTaxAssetsandLiabilitiesDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#IncomeTaxesTaxEffectsofTemporaryDifferencesThatGiveRisetoSignificantPortionsofDeferredTaxAssetsandLiabilitiesDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/IncomeTaxesTaxEffectsofTemporaryDifferencesThatGiveRisetoSignificantPortionsofDeferredTaxAssetsandLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxLiabilities_32e98b57-c3e2-4b77-a5dd-7cabeadbbe08" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxLiabilities"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilities_a2246951-fb17-4d3f-837b-725d25ba7ba5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredIncomeTaxLiabilities"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxLiabilities_32e98b57-c3e2-4b77-a5dd-7cabeadbbe08" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilities_a2246951-fb17-4d3f-837b-725d25ba7ba5" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsNet_5b30a77c-4209-47c1-ae36-463f211035d2" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsNet"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxLiabilities_32e98b57-c3e2-4b77-a5dd-7cabeadbbe08" xlink:to="loc_us-gaap_DeferredTaxAssetsNet_5b30a77c-4209-47c1-ae36-463f211035d2" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsGross_6c8dc876-0eab-405b-95fb-255cb92f40da" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsGross"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_DeferredTaxAssetsOperatingLossAndTaxCreditsCarryforwards_afa2fb64-6d85-4e6e-927a-d617c3c23d4e" xlink:href="iclr-20221231.xsd#iclr_DeferredTaxAssetsOperatingLossAndTaxCreditsCarryforwards"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsGross_6c8dc876-0eab-405b-95fb-255cb92f40da" xlink:to="loc_iclr_DeferredTaxAssetsOperatingLossAndTaxCreditsCarryforwards_afa2fb64-6d85-4e6e-927a-d617c3c23d4e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsPropertyPlantAndEquipment_4dabc5d3-a7f3-4a4f-9646-c32422cbf9c5" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsPropertyPlantAndEquipment"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsGross_6c8dc876-0eab-405b-95fb-255cb92f40da" xlink:to="loc_us-gaap_DeferredTaxAssetsPropertyPlantAndEquipment_4dabc5d3-a7f3-4a4f-9646-c32422cbf9c5" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_DeferredTaxAssetsOperatingLeaseLiability_ef83dd45-8024-4880-95de-7126340de51c" xlink:href="iclr-20221231.xsd#iclr_DeferredTaxAssetsOperatingLeaseLiability"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsGross_6c8dc876-0eab-405b-95fb-255cb92f40da" xlink:to="loc_iclr_DeferredTaxAssetsOperatingLeaseLiability_ef83dd45-8024-4880-95de-7126340de51c" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAccruedLiabilities_93148d2d-cc53-40c8-99e0-03fd4713ac9c" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAccruedLiabilities"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsGross_6c8dc876-0eab-405b-95fb-255cb92f40da" xlink:to="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAccruedLiabilities_93148d2d-cc53-40c8-99e0-03fd4713ac9c" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsOther_a279195b-cea2-49f3-86fb-105f10f5ed50" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsOther"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsGross_6c8dc876-0eab-405b-95fb-255cb92f40da" xlink:to="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsOther_a279195b-cea2-49f3-86fb-105f10f5ed50" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefits_dbc2491d-e4b2-493c-ab8e-f319f3feb068" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefits"/>
    <link:calculationArc order="6" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsGross_6c8dc876-0eab-405b-95fb-255cb92f40da" xlink:to="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefits_dbc2491d-e4b2-493c-ab8e-f319f3feb068" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_DeferredTaxAssetContractWithCustomerLiability_241a221e-ecf9-4205-aeee-b8393c5b2dd8" xlink:href="iclr-20221231.xsd#iclr_DeferredTaxAssetContractWithCustomerLiability"/>
    <link:calculationArc order="7" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsGross_6c8dc876-0eab-405b-95fb-255cb92f40da" xlink:to="loc_iclr_DeferredTaxAssetContractWithCustomerLiability_241a221e-ecf9-4205-aeee-b8393c5b2dd8" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpenseOther_6f9822c9-9e5f-4e4d-ae4d-e0cddc728fa6" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsTaxDeferredExpenseOther"/>
    <link:calculationArc order="8" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsGross_6c8dc876-0eab-405b-95fb-255cb92f40da" xlink:to="loc_us-gaap_DeferredTaxAssetsTaxDeferredExpenseOther_6f9822c9-9e5f-4e4d-ae4d-e0cddc728fa6" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsGoodwillAndIntangibleAssets_71d7ed96-62ce-40e6-bba2-e3e271c0cf4a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsGoodwillAndIntangibleAssets"/>
    <link:calculationArc order="9" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsGross_6c8dc876-0eab-405b-95fb-255cb92f40da" xlink:to="loc_us-gaap_DeferredTaxAssetsGoodwillAndIntangibleAssets_71d7ed96-62ce-40e6-bba2-e3e271c0cf4a" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsNet_f7c99471-755d-4f11-9d15-23e0d500a833" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsNet"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsGross_8b5861a9-bc77-444b-b0bd-202ac41b2ea3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsGross"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsNet_f7c99471-755d-4f11-9d15-23e0d500a833" xlink:to="loc_us-gaap_DeferredTaxAssetsGross_8b5861a9-bc77-444b-b0bd-202ac41b2ea3" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsValuationAllowance_5b446d9e-4c42-4a1f-bbb9-38ebf5bdb6a4" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsValuationAllowance"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsNet_f7c99471-755d-4f11-9d15-23e0d500a833" xlink:to="loc_us-gaap_DeferredTaxAssetsValuationAllowance_5b446d9e-4c42-4a1f-bbb9-38ebf5bdb6a4" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilities_2bddc62e-60e6-4039-88e1-8297a9b8c864" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredIncomeTaxLiabilities"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxLiabilitiesOtherFiniteLivedAssets_52bcfa37-4861-48d0-8d56-0d4312861ef0" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxLiabilitiesOtherFiniteLivedAssets"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredIncomeTaxLiabilities_2bddc62e-60e6-4039-88e1-8297a9b8c864" xlink:to="loc_us-gaap_DeferredTaxLiabilitiesOtherFiniteLivedAssets_52bcfa37-4861-48d0-8d56-0d4312861ef0" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxLiabilitiesOther_81c8aaba-5462-4493-ab96-5311ae6d0c5a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxLiabilitiesOther"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredIncomeTaxLiabilities_2bddc62e-60e6-4039-88e1-8297a9b8c864" xlink:to="loc_us-gaap_DeferredTaxLiabilitiesOther_81c8aaba-5462-4493-ab96-5311ae6d0c5a" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxLiabilitiesLeasingArrangements_5048ff8a-0df6-4a6a-bdc8-124b3f3dcda1" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxLiabilitiesLeasingArrangements"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredIncomeTaxLiabilities_2bddc62e-60e6-4039-88e1-8297a9b8c864" xlink:to="loc_us-gaap_DeferredTaxLiabilitiesLeasingArrangements_5048ff8a-0df6-4a6a-bdc8-124b3f3dcda1" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment_a340a82d-0ac4-4a60-9526-da4e331556db" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredIncomeTaxLiabilities_2bddc62e-60e6-4039-88e1-8297a9b8c864" xlink:to="loc_us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment_a340a82d-0ac4-4a60-9526-da4e331556db" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsGoodwill_60698f11-dc12-4768-8ba0-910958273afb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsGoodwill"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredIncomeTaxLiabilities_2bddc62e-60e6-4039-88e1-8297a9b8c864" xlink:to="loc_us-gaap_DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsGoodwill_60698f11-dc12-4768-8ba0-910958273afb" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/IncomeTaxesExpectedExpiryDatesofNOLsDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#IncomeTaxesExpectedExpiryDatesofNOLsDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/IncomeTaxesExpectedExpiryDatesofNOLsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_ebb3e39a-467f-4b5a-94ce-407f6ae6184a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwards"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration_5100c80f-396c-4d3b-a446-1a6892cd2c81" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_ebb3e39a-467f-4b5a-94ce-407f6ae6184a" xlink:to="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration_5100c80f-396c-4d3b-a446-1a6892cd2c81" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration_bd553c9c-8377-4464-aca6-ea839ef3e636" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_ebb3e39a-467f-4b5a-94ce-407f6ae6184a" xlink:to="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration_bd553c9c-8377-4464-aca6-ea839ef3e636" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/EmployeeBenefitsFundedStatusDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#EmployeeBenefitsFundedStatusDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/EmployeeBenefitsFundedStatusDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlan_7d27a39f-8684-4624-b74e-b269013f220a" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanFundedStatusOfPlan"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateProjectedBenefitObligation_685a9519-bb6c-4853-9153-92411a0011cc" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateProjectedBenefitObligation"/>
    <link:calculationArc order="1" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlan_7d27a39f-8684-4624-b74e-b269013f220a" xlink:to="loc_us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateProjectedBenefitObligation_685a9519-bb6c-4853-9153-92411a0011cc" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_4b0cf0ea-bb35-4d60-9580-a87c5b52a817" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlan_7d27a39f-8684-4624-b74e-b269013f220a" xlink:to="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_4b0cf0ea-bb35-4d60-9580-a87c5b52a817" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/EmployeeBenefitsComponentsofNetPeriodicBenefitCostDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#EmployeeBenefitsComponentsofNetPeriodicBenefitCostDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/EmployeeBenefitsComponentsofNetPeriodicBenefitCostDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_d2b89f75-50af-421a-b8fa-e3ad6bbcfd1e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_b2dd8508-90c1-4e27-b38e-2d009f8c8aa7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses"/>
    <link:calculationArc order="1" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_d2b89f75-50af-421a-b8fa-e3ad6bbcfd1e" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_b2dd8508-90c1-4e27-b38e-2d009f8c8aa7" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanServiceCost_42a00952-e658-44ed-a1d2-93a787c625cf" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanServiceCost"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_d2b89f75-50af-421a-b8fa-e3ad6bbcfd1e" xlink:to="loc_us-gaap_DefinedBenefitPlanServiceCost_42a00952-e658-44ed-a1d2-93a787c625cf" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_ee09074a-5f96-43e4-925f-19be448a83a8" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets"/>
    <link:calculationArc order="3" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_d2b89f75-50af-421a-b8fa-e3ad6bbcfd1e" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_ee09074a-5f96-43e4-925f-19be448a83a8" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanInterestCost_1cfe3685-23a1-47d2-b4b5-7e73f049aac7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DefinedBenefitPlanInterestCost"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_d2b89f75-50af-421a-b8fa-e3ad6bbcfd1e" xlink:to="loc_us-gaap_DefinedBenefitPlanInterestCost_1cfe3685-23a1-47d2-b4b5-7e73f049aac7" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/EmployeeBenefitsNetPeriodicPensionBenefitCostAssumptionsDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#EmployeeBenefitsNetPeriodicPensionBenefitCostAssumptionsDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/EmployeeBenefitsNetPeriodicPensionBenefitCostAssumptionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_27c3a557-c992-4bcd-9422-9f1f8b0e1deb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_DefinedBenefitPlanActuarialLossesToBeAmortizedAndReclassifiedFromAccumulatedOtherComprehensiveIncomeLossToNetPensionCost_c94c1a78-2e36-4fa7-9870-69123094d4cc" xlink:href="iclr-20221231.xsd#iclr_DefinedBenefitPlanActuarialLossesToBeAmortizedAndReclassifiedFromAccumulatedOtherComprehensiveIncomeLossToNetPensionCost"/>
    <link:calculationArc order="1" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_27c3a557-c992-4bcd-9422-9f1f8b0e1deb" xlink:to="loc_iclr_DefinedBenefitPlanActuarialLossesToBeAmortizedAndReclassifiedFromAccumulatedOtherComprehensiveIncomeLossToNetPensionCost_c94c1a78-2e36-4fa7-9870-69123094d4cc" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax_3df8de05-b16c-404a-aac5-cbe2e40636b7" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_27c3a557-c992-4bcd-9422-9f1f8b0e1deb" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax_3df8de05-b16c-404a-aac5-cbe2e40636b7" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_OtherComprehensiveIncomeAmortizationOfNetActuarialGainLossNetOfTax_595a59ec-a9bf-425a-8961-a76c1e3d3123" xlink:href="iclr-20221231.xsd#iclr_OtherComprehensiveIncomeAmortizationOfNetActuarialGainLossNetOfTax"/>
    <link:calculationArc order="3" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetTransitionAssetObligationNetOfTax_27c3a557-c992-4bcd-9422-9f1f8b0e1deb" xlink:to="loc_iclr_OtherComprehensiveIncomeAmortizationOfNetActuarialGainLossNetOfTax_595a59ec-a9bf-425a-8961-a76c1e3d3123" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/NetIncomePerOrdinaryShareReconciliationofNumberofSharesUsedinComputationofBasicandDilutedNetIncomePerOrdinaryShareDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#NetIncomePerOrdinaryShareReconciliationofNumberofSharesUsedinComputationofBasicandDilutedNetIncomePerOrdinaryShareDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/NetIncomePerOrdinaryShareReconciliationofNumberofSharesUsedinComputationofBasicandDilutedNetIncomePerOrdinaryShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_afcab9fb-63bb-4931-988d-acd77fbcb47e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_825f988b-2354-413b-8576-e7ae7f011e9d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_afcab9fb-63bb-4931-988d-acd77fbcb47e" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_825f988b-2354-413b-8576-e7ae7f011e9d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment_f71f81c7-ed20-4cd7-9e81-f8e7839a92a3" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_afcab9fb-63bb-4931-988d-acd77fbcb47e" xlink:to="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment_f71f81c7-ed20-4cd7-9e81-f8e7839a92a3" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/NetIncomePerOrdinaryShareReconciliationofNetIncomeAttributabletotheGroupPertheStatementofOperatingIncomeandNetIncomeUsedForNetIncomePerOrdinaryShareDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#NetIncomePerOrdinaryShareReconciliationofNetIncomeAttributabletotheGroupPertheStatementofOperatingIncomeandNetIncomeUsedForNetIncomePerOrdinaryShareDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/NetIncomePerOrdinaryShareReconciliationofNetIncomeAttributabletotheGroupPertheStatementofOperatingIncomeandNetIncomeUsedForNetIncomePerOrdinaryShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_9ef99747-4561-49aa-b754-1f9cf580c855" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_1ca135cb-718a-4815-9de9-1842cd430652" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLoss"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_9ef99747-4561-49aa-b754-1f9cf580c855" xlink:to="loc_us-gaap_NetIncomeLoss_1ca135cb-718a-4815-9de9-1842cd430652" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_8fca11ea-93a2-4802-86a1-8097200bcf35" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_9ef99747-4561-49aa-b754-1f9cf580c855" xlink:to="loc_us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_8fca11ea-93a2-4802-86a1-8097200bcf35" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.iconplc.com/role/AccumulatedOtherComprehensiveIncomeDetails" xlink:type="simple" xlink:href="iclr-20221231.xsd#AccumulatedOtherComprehensiveIncomeDetails"/>
  <link:calculationLink xlink:role="http://www.iconplc.com/role/AccumulatedOtherComprehensiveIncomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_48fdfc1f-9fde-4977-b674-b0006c60423e" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_AccumulatedOtherComprehensiveLossAmortizationOfCashFlowHedgesEffectNetOfTax_4038f2ce-5da7-4b82-b9c4-c3818c714d0c" xlink:href="iclr-20221231.xsd#iclr_AccumulatedOtherComprehensiveLossAmortizationOfCashFlowHedgesEffectNetOfTax"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_48fdfc1f-9fde-4977-b674-b0006c60423e" xlink:to="loc_iclr_AccumulatedOtherComprehensiveLossAmortizationOfCashFlowHedgesEffectNetOfTax_4038f2ce-5da7-4b82-b9c4-c3818c714d0c" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_iclr_AcumulatedOtherComprehensiveLossCashFlowHedgeLossReclassificationAfterTax_0d8c7800-0550-4b5c-a09f-d56713f4b28f" xlink:href="iclr-20221231.xsd#iclr_AcumulatedOtherComprehensiveLossCashFlowHedgeLossReclassificationAfterTax"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_48fdfc1f-9fde-4977-b674-b0006c60423e" xlink:to="loc_iclr_AcumulatedOtherComprehensiveLossCashFlowHedgeLossReclassificationAfterTax_0d8c7800-0550-4b5c-a09f-d56713f4b28f" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax_9e338ffd-8e49-42a0-b019-b173e7766e4d" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax"/>
    <link:calculationArc order="3" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_48fdfc1f-9fde-4977-b674-b0006c60423e" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossDefinedBenefitPensionAndOtherPostretirementPlansNetOfTax_9e338ffd-8e49-42a0-b019-b173e7766e4d" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax_b16847df-0e42-47e7-a72d-005c57b30dcb" xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_48fdfc1f-9fde-4977-b674-b0006c60423e" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentNetOfTax_b16847df-0e42-47e7-a72d-005c57b30dcb" xlink:type="arc"/>
  </link:calculationLink>
</link:linkbase>
