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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2023 Workiva-->
<!--r:8d104aa4-bb67-44f2-927c-dc59806c2234,g:426b6d97-1d10-4305-85c1-d8e216bc6355-->
<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.pliantrx.com/role/CondensedBalanceSheetsUnaudited" xlink:type="simple" xlink:href="plrx-20230630.xsd#CondensedBalanceSheetsUnaudited"/>
  <link:calculationLink xlink:role="http://www.pliantrx.com/role/CondensedBalanceSheetsUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_f0d3c350-f44e-402f-a82e-2f6087418371" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Liabilities"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_f06b5d53-467e-4009-94f1-a4363b27426a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_f0d3c350-f44e-402f-a82e-2f6087418371" xlink:to="loc_us-gaap_LiabilitiesCurrent_f06b5d53-467e-4009-94f1-a4363b27426a" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_3326216e-7187-434d-84fc-5c7a80cdc29b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_f0d3c350-f44e-402f-a82e-2f6087418371" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_3326216e-7187-434d-84fc-5c7a80cdc29b" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_20db5964-ce6c-469f-a9c6-4477195b2d73" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebt"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_f0d3c350-f44e-402f-a82e-2f6087418371" xlink:to="loc_us-gaap_LongTermDebt_20db5964-ce6c-469f-a9c6-4477195b2d73" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_fe034d29-c312-48ab-b55a-69b1bc323caf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Assets"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_0c42ce65-038e-4339-987d-6fd8df6a4941" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsCurrent"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_fe034d29-c312-48ab-b55a-69b1bc323caf" xlink:to="loc_us-gaap_AssetsCurrent_0c42ce65-038e-4339-987d-6fd8df6a4941" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_45fed098-5421-4c46-8106-7faa5317741b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_fe034d29-c312-48ab-b55a-69b1bc323caf" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_45fed098-5421-4c46-8106-7faa5317741b" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_f2da1e98-4890-441a-a563-fc72304bc949" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_fe034d29-c312-48ab-b55a-69b1bc323caf" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_f2da1e98-4890-441a-a563-fc72304bc949" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_f36e9b08-c832-4d71-a4f7-b34ebb250663" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_fe034d29-c312-48ab-b55a-69b1bc323caf" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_f36e9b08-c832-4d71-a4f7-b34ebb250663" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_e3849d1a-9010-46e3-9047-420c7473c226" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_de3e49eb-7817-47da-a0f9-0aff3b1139d5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_e3849d1a-9010-46e3-9047-420c7473c226" xlink:to="loc_us-gaap_Liabilities_de3e49eb-7817-47da-a0f9-0aff3b1139d5" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_f5b56bb4-b6b3-4ffb-ad49-3a31c83269c3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_e3849d1a-9010-46e3-9047-420c7473c226" xlink:to="loc_us-gaap_StockholdersEquity_f5b56bb4-b6b3-4ffb-ad49-3a31c83269c3" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_14307a85-c7e5-40e9-ad42-8111c0781fb4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_fc30854e-a347-4ea0-b6f8-e3b40fc647b3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_14307a85-c7e5-40e9-ad42-8111c0781fb4" xlink:to="loc_us-gaap_CommonStockValue_fc30854e-a347-4ea0-b6f8-e3b40fc647b3" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_fac3b131-960b-4f35-a106-3817c16b8728" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_14307a85-c7e5-40e9-ad42-8111c0781fb4" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_fac3b131-960b-4f35-a106-3817c16b8728" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_5405548d-9990-4ecb-8a38-fea74949acb9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_14307a85-c7e5-40e9-ad42-8111c0781fb4" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_5405548d-9990-4ecb-8a38-fea74949acb9" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_1cda8c88-4c71-46ca-9338-9a51f8ac19cb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_14307a85-c7e5-40e9-ad42-8111c0781fb4" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_1cda8c88-4c71-46ca-9338-9a51f8ac19cb" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_12b8453b-c005-4b54-bcf6-80d2f73a948a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_7706a9bb-956c-42e8-b427-f65690dc40a6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesCurrent_12b8453b-c005-4b54-bcf6-80d2f73a948a" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_7706a9bb-956c-42e8-b427-f65690dc40a6" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_plrx_AccruedResearchAndDevelopmentExpensesCurrent_7a1dbe96-80cd-45c0-8315-ccc8421cc5b4" xlink:href="plrx-20230630.xsd#plrx_AccruedResearchAndDevelopmentExpensesCurrent"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesCurrent_12b8453b-c005-4b54-bcf6-80d2f73a948a" xlink:to="loc_plrx_AccruedResearchAndDevelopmentExpensesCurrent_7a1dbe96-80cd-45c0-8315-ccc8421cc5b4" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_a80cf52e-9ebd-49b7-8445-2391fe970bc1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesCurrent_12b8453b-c005-4b54-bcf6-80d2f73a948a" xlink:to="loc_us-gaap_AccountsPayableCurrent_a80cf52e-9ebd-49b7-8445-2391fe970bc1" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_d0493645-e676-4acd-84c6-e04a21d9e5ee" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesCurrent_12b8453b-c005-4b54-bcf6-80d2f73a948a" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_d0493645-e676-4acd-84c6-e04a21d9e5ee" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_205fd866-af17-4f78-86cb-865a362f8e5d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsCurrent"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_6b952468-fa6e-444f-89b1-6a2e0d05083f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_205fd866-af17-4f78-86cb-865a362f8e5d" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_6b952468-fa6e-444f-89b1-6a2e0d05083f" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermInvestments_a445e36b-0724-466c-afd3-6f334c147e0f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShortTermInvestments"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_205fd866-af17-4f78-86cb-865a362f8e5d" xlink:to="loc_us-gaap_ShortTermInvestments_a445e36b-0724-466c-afd3-6f334c147e0f" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_2150afcd-b50a-46a3-8e33-2cffcdc3086c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_205fd866-af17-4f78-86cb-865a362f8e5d" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_2150afcd-b50a-46a3-8e33-2cffcdc3086c" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesReceivable_3c1897a8-ed01-4c5e-b699-31498283bcd6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxesReceivable"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_205fd866-af17-4f78-86cb-865a362f8e5d" xlink:to="loc_us-gaap_IncomeTaxesReceivable_3c1897a8-ed01-4c5e-b699-31498283bcd6" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_715f3cd6-4d9f-463c-8a78-6c23d1d42bb0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_205fd866-af17-4f78-86cb-865a362f8e5d" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_715f3cd6-4d9f-463c-8a78-6c23d1d42bb0" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.pliantrx.com/role/CondensedStatementsofOperationsandComprehensiveLossUnaudited" xlink:type="simple" xlink:href="plrx-20230630.xsd#CondensedStatementsofOperationsandComprehensiveLossUnaudited"/>
  <link:calculationLink xlink:role="http://www.pliantrx.com/role/CondensedStatementsofOperationsandComprehensiveLossUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_8abd5488-c5a3-4908-a186-26893b76ee51" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_ef4f16b1-6dba-4198-a760-b93c251be484" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_8abd5488-c5a3-4908-a186-26893b76ee51" xlink:to="loc_us-gaap_NetIncomeLoss_ef4f16b1-6dba-4198-a760-b93c251be484" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_395d2304-2056-4034-ba49-4574cb254645" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_f42b00a8-a668-4380-bf32-f4995e5f0611" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_395d2304-2056-4034-ba49-4574cb254645" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_f42b00a8-a668-4380-bf32-f4995e5f0611" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_6fed0e57-0673-431b-bb7d-0b61436fb4c3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_b51cc85f-9829-4575-b2fe-b63a845dc3cb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_NetIncomeLossAvailableToCommonStockholdersDiluted_6fed0e57-0673-431b-bb7d-0b61436fb4c3" xlink:to="loc_us-gaap_NetIncomeLoss_b51cc85f-9829-4575-b2fe-b63a845dc3cb" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_2db53a41-6d7b-475a-a7ca-d13107f47a87" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingExpenses"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_1fd8e9e7-a8ad-4c69-84ac-ef43c6d1a19b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingExpenses_2db53a41-6d7b-475a-a7ca-d13107f47a87" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_1fd8e9e7-a8ad-4c69-84ac-ef43c6d1a19b" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_e9ab5657-21af-44bc-8d96-6a4deb63ccec" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingExpenses_2db53a41-6d7b-475a-a7ca-d13107f47a87" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_e9ab5657-21af-44bc-8d96-6a4deb63ccec" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_d6a01a79-991f-47ed-8d3c-2ce688707d4e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_9a928127-f6b2-4940-9e7b-a4b4f2a40fac" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingIncomeLoss_d6a01a79-991f-47ed-8d3c-2ce688707d4e" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_9a928127-f6b2-4940-9e7b-a4b4f2a40fac" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_510dcb41-f81e-4dd0-b48d-952246172e87" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingExpenses"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingIncomeLoss_d6a01a79-991f-47ed-8d3c-2ce688707d4e" xlink:to="loc_us-gaap_OperatingExpenses_510dcb41-f81e-4dd0-b48d-952246172e87" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_6761225c-6209-4f89-ac56-794515428fb1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_cc815e78-f876-4261-8e9e-3f0a38b24d1f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_ComprehensiveIncomeNetOfTax_6761225c-6209-4f89-ac56-794515428fb1" xlink:to="loc_us-gaap_NetIncomeLoss_cc815e78-f876-4261-8e9e-3f0a38b24d1f" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_16f442e2-c6f5-431c-84e9-75d258d99418" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTax_6761225c-6209-4f89-ac56-794515428fb1" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_16f442e2-c6f5-431c-84e9-75d258d99418" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_7502dc94-c471-4fb6-a776-c0475d5d0562" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLoss"/>
    <link:loc xlink:type="locator" xlink:label="loc_plrx_InterestAndOtherIncomeExpenseNet_fec28d19-01f3-42aa-bcab-bb2259a29687" xlink:href="plrx-20230630.xsd#plrx_InterestAndOtherIncomeExpenseNet"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetIncomeLoss_7502dc94-c471-4fb6-a776-c0475d5d0562" xlink:to="loc_plrx_InterestAndOtherIncomeExpenseNet_fec28d19-01f3-42aa-bcab-bb2259a29687" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_228550f3-6114-409d-b452-5538d0a51e26" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetIncomeLoss_7502dc94-c471-4fb6-a776-c0475d5d0562" xlink:to="loc_us-gaap_OperatingIncomeLoss_228550f3-6114-409d-b452-5538d0a51e26" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_4d88ced5-3a4b-4fac-86fe-d8f98cce3781" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_NetIncomeLoss_7502dc94-c471-4fb6-a776-c0475d5d0562" xlink:to="loc_us-gaap_InterestExpense_4d88ced5-3a4b-4fac-86fe-d8f98cce3781" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.pliantrx.com/role/CondensedStatementsofCashFlowsUnaudited" xlink:type="simple" xlink:href="plrx-20230630.xsd#CondensedStatementsofCashFlowsUnaudited"/>
  <link:calculationLink xlink:role="http://www.pliantrx.com/role/CondensedStatementsofCashFlowsUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_2a5d1d78-d61a-4b64-b24c-9b3c5f38e6c2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDebtIssuanceCosts_40f5fbab-12ec-4de7-a2cc-ca94d7d8a634" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsOfDebtIssuanceCosts"/>
    <link:calculationArc order="1" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_2a5d1d78-d61a-4b64-b24c-9b3c5f38e6c2" xlink:to="loc_us-gaap_PaymentsOfDebtIssuanceCosts_40f5fbab-12ec-4de7-a2cc-ca94d7d8a634" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_plrx_PaymentsOfDeferredOfferingCosts_3df47891-44af-4d8e-b3ff-d0a38574d8a0" xlink:href="plrx-20230630.xsd#plrx_PaymentsOfDeferredOfferingCosts"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_2a5d1d78-d61a-4b64-b24c-9b3c5f38e6c2" xlink:to="loc_plrx_PaymentsOfDeferredOfferingCosts_3df47891-44af-4d8e-b3ff-d0a38574d8a0" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_7906e28a-78df-4bd7-bb90-413dfdb5b6b9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromIssuanceOfDebt"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_2a5d1d78-d61a-4b64-b24c-9b3c5f38e6c2" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_7906e28a-78df-4bd7-bb90-413dfdb5b6b9" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_plrx_ProceedsFromIssuancesOfCommonStockUnderBenefitPlans_d6a6da2e-ea4c-4f30-bdf7-9cb9eb71bc68" xlink:href="plrx-20230630.xsd#plrx_ProceedsFromIssuancesOfCommonStockUnderBenefitPlans"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_2a5d1d78-d61a-4b64-b24c-9b3c5f38e6c2" xlink:to="loc_plrx_ProceedsFromIssuancesOfCommonStockUnderBenefitPlans_d6a6da2e-ea4c-4f30-bdf7-9cb9eb71bc68" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceInitialPublicOffering_e1341a73-41e7-4518-a951-a7c633a5686e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromIssuanceInitialPublicOffering"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_2a5d1d78-d61a-4b64-b24c-9b3c5f38e6c2" xlink:to="loc_us-gaap_ProceedsFromIssuanceInitialPublicOffering_e1341a73-41e7-4518-a951-a7c633a5686e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_44afb257-fc5a-4b27-acc3-4658489df52a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_3cdb2163-ccb2-4a73-b80a-3e4922dcd265" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensation"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_44afb257-fc5a-4b27-acc3-4658489df52a" xlink:to="loc_us-gaap_ShareBasedCompensation_3cdb2163-ccb2-4a73-b80a-3e4922dcd265" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense_6330437d-12a3-47c1-83fa-c7265b494c3a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_44afb257-fc5a-4b27-acc3-4658489df52a" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAssetAmortizationExpense_6330437d-12a3-47c1-83fa-c7265b494c3a" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_98841dd8-0bee-4350-8c1a-3a8a4887659c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Depreciation"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_44afb257-fc5a-4b27-acc3-4658489df52a" xlink:to="loc_us-gaap_Depreciation_98841dd8-0bee-4350-8c1a-3a8a4887659c" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_a3e37a48-09df-4946-8f97-506071f0ca50" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments"/>
    <link:calculationArc order="4" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_44afb257-fc5a-4b27-acc3-4658489df52a" xlink:to="loc_us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_a3e37a48-09df-4946-8f97-506071f0ca50" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_2aff68c4-905b-4396-b232-5ff96a6a53f1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLoss"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_44afb257-fc5a-4b27-acc3-4658489df52a" xlink:to="loc_us-gaap_NetIncomeLoss_2aff68c4-905b-4396-b232-5ff96a6a53f1" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingLeaseLiability_24423830-32f4-4c69-847a-3ab41a7cf1af" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInOperatingLeaseLiability"/>
    <link:calculationArc order="6" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_44afb257-fc5a-4b27-acc3-4658489df52a" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingLeaseLiability_24423830-32f4-4c69-847a-3ab41a7cf1af" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_93a72730-1037-49ab-b872-f3c224a8f124" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities"/>
    <link:calculationArc order="7" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_44afb257-fc5a-4b27-acc3-4658489df52a" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_93a72730-1037-49ab-b872-f3c224a8f124" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_75066ec8-2d3c-4d1c-b29c-6e6b90dcac0a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets"/>
    <link:calculationArc order="8" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_44afb257-fc5a-4b27-acc3-4658489df52a" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_75066ec8-2d3c-4d1c-b29c-6e6b90dcac0a" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_9dc824ca-c25a-42eb-90f9-c026bcdbef4e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable"/>
    <link:calculationArc order="9" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_44afb257-fc5a-4b27-acc3-4658489df52a" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_9dc824ca-c25a-42eb-90f9-c026bcdbef4e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_54cf44ce-a7e1-4603-bdc1-4ef61683c137" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInAccountsPayable"/>
    <link:calculationArc order="10" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_44afb257-fc5a-4b27-acc3-4658489df52a" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_54cf44ce-a7e1-4603-bdc1-4ef61683c137" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_018d47a3-7c05-41aa-ac5b-66f484c8e033" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfShorttermInvestments_bb7361c2-1f9a-44cd-b9c2-c820ce97459c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfShorttermInvestments"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_018d47a3-7c05-41aa-ac5b-66f484c8e033" xlink:to="loc_us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfShorttermInvestments_bb7361c2-1f9a-44cd-b9c2-c820ce97459c" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireShortTermInvestments_e6687dcb-cfcd-4fdc-a801-afb9a3a36f58" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquireShortTermInvestments"/>
    <link:calculationArc order="2" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_018d47a3-7c05-41aa-ac5b-66f484c8e033" xlink:to="loc_us-gaap_PaymentsToAcquireShortTermInvestments_e6687dcb-cfcd-4fdc-a801-afb9a3a36f58" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_0d4ff8de-79d9-4de1-8403-717e5f24ce70" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:calculationArc order="3" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_018d47a3-7c05-41aa-ac5b-66f484c8e033" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_0d4ff8de-79d9-4de1-8403-717e5f24ce70" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_0819d67c-5aac-41f6-bed9-56c0046e684d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_d65adbbe-2c2f-4400-a96e-03a0a0d78e0e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_0819d67c-5aac-41f6-bed9-56c0046e684d" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_d65adbbe-2c2f-4400-a96e-03a0a0d78e0e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_ce533eab-0e4f-4779-8ed2-74859f903488" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_0819d67c-5aac-41f6-bed9-56c0046e684d" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_ce533eab-0e4f-4779-8ed2-74859f903488" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_9e243cf1-b108-4253-987f-df82d87ec417" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_0819d67c-5aac-41f6-bed9-56c0046e684d" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_9e243cf1-b108-4253-987f-df82d87ec417" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.pliantrx.com/role/FinancialInstrumentsSummaryofCashandCashEquivalentsMoneyMarketFundsandShorttermInvestmentsbySignificantInvestmentCategoryDetails" xlink:type="simple" xlink:href="plrx-20230630.xsd#FinancialInstrumentsSummaryofCashandCashEquivalentsMoneyMarketFundsandShorttermInvestmentsbySignificantInvestmentCategoryDetails"/>
  <link:calculationLink xlink:role="http://www.pliantrx.com/role/FinancialInstrumentsSummaryofCashandCashEquivalentsMoneyMarketFundsandShorttermInvestmentsbySignificantInvestmentCategoryDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_a7661df5-0573-4b40-95e6-1dd8e5ae4618" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_ab76e467-6717-4a18-9a6a-f1d0f3387c1e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:calculationArc order="1" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_a7661df5-0573-4b40-95e6-1dd8e5ae4618" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_ab76e467-6717-4a18-9a6a-f1d0f3387c1e" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_fd64cb93-548f-438c-a959-5016514c5f41" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_a7661df5-0573-4b40-95e6-1dd8e5ae4618" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_fd64cb93-548f-438c-a959-5016514c5f41" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_d9515c5f-cb4f-4417-81fe-570c8bdd60d0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_a7661df5-0573-4b40-95e6-1dd8e5ae4618" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_d9515c5f-cb4f-4417-81fe-570c8bdd60d0" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.pliantrx.com/role/PropertyandEquipmentnetScheduleofPropertyandEquipmentDetails" xlink:type="simple" xlink:href="plrx-20230630.xsd#PropertyandEquipmentnetScheduleofPropertyandEquipmentDetails"/>
  <link:calculationLink xlink:role="http://www.pliantrx.com/role/PropertyandEquipmentnetScheduleofPropertyandEquipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_6c184932-ed3a-4213-8f8f-233a8a51ac57" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_ebaa5a72-0771-495e-b549-82ba8fbb44c2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_6c184932-ed3a-4213-8f8f-233a8a51ac57" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_ebaa5a72-0771-495e-b549-82ba8fbb44c2" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_3446b85f-6791-42c0-a710-0bb98ce9d1f0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.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_6c184932-ed3a-4213-8f8f-233a8a51ac57" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_3446b85f-6791-42c0-a710-0bb98ce9d1f0" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.pliantrx.com/role/PrepaidExpensesandOtherCurrentAssetsDetails" xlink:type="simple" xlink:href="plrx-20230630.xsd#PrepaidExpensesandOtherCurrentAssetsDetails"/>
  <link:calculationLink xlink:role="http://www.pliantrx.com/role/PrepaidExpensesandOtherCurrentAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_4a0b32a6-5675-4ca2-807c-4fa14aaf5f95" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:loc xlink:type="locator" xlink:label="loc_plrx_PrepaidResearchAndDevelopmentCurrent_92cb17eb-c433-442a-ab0a-3c4f3aaceed0" xlink:href="plrx-20230630.xsd#plrx_PrepaidResearchAndDevelopmentCurrent"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_4a0b32a6-5675-4ca2-807c-4fa14aaf5f95" xlink:to="loc_plrx_PrepaidResearchAndDevelopmentCurrent_92cb17eb-c433-442a-ab0a-3c4f3aaceed0" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidInsurance_596d30fd-5a15-4b54-bd00-316340a7b2fc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PrepaidInsurance"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_4a0b32a6-5675-4ca2-807c-4fa14aaf5f95" xlink:to="loc_us-gaap_PrepaidInsurance_596d30fd-5a15-4b54-bd00-316340a7b2fc" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_plrx_PrepaidLicensesCurrent_c1d09989-fcdf-439f-b4a8-5d731ecab883" xlink:href="plrx-20230630.xsd#plrx_PrepaidLicensesCurrent"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_4a0b32a6-5675-4ca2-807c-4fa14aaf5f95" xlink:to="loc_plrx_PrepaidLicensesCurrent_c1d09989-fcdf-439f-b4a8-5d731ecab883" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestReceivableCurrent_02c4f5c9-b6da-42eb-a2d6-74b2eb259bcd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InterestReceivableCurrent"/>
    <link:calculationArc order="4" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_4a0b32a6-5675-4ca2-807c-4fa14aaf5f95" xlink:to="loc_us-gaap_InterestReceivableCurrent_02c4f5c9-b6da-42eb-a2d6-74b2eb259bcd" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPrepaidExpenseCurrent_12f2fef8-f4fd-4708-a3d4-598593732f7b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherPrepaidExpenseCurrent"/>
    <link:calculationArc order="5" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_4a0b32a6-5675-4ca2-807c-4fa14aaf5f95" xlink:to="loc_us-gaap_OtherPrepaidExpenseCurrent_12f2fef8-f4fd-4708-a3d4-598593732f7b" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.pliantrx.com/role/AccruedLiabilitiesSummaryofAccruedLiabilitiesDetails" xlink:type="simple" xlink:href="plrx-20230630.xsd#AccruedLiabilitiesSummaryofAccruedLiabilitiesDetails"/>
  <link:calculationLink xlink:role="http://www.pliantrx.com/role/AccruedLiabilitiesSummaryofAccruedLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_dd66d4a5-1f4e-4ab9-9be6-03956f4daf44" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_2e795f59-f1ce-476f-83e9-fe4fd5d924e9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrent"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AccruedLiabilitiesCurrent_dd66d4a5-1f4e-4ab9-9be6-03956f4daf44" xlink:to="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_2e795f59-f1ce-476f-83e9-fe4fd5d924e9" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndOtherAccruedLiabilitiesCurrent_1ababe73-73ae-416d-9806-08cb0649c0e5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsPayableAndOtherAccruedLiabilitiesCurrent"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AccruedLiabilitiesCurrent_dd66d4a5-1f4e-4ab9-9be6-03956f4daf44" xlink:to="loc_us-gaap_AccountsPayableAndOtherAccruedLiabilitiesCurrent_1ababe73-73ae-416d-9806-08cb0649c0e5" xlink:type="arc"/>
  </link:calculationLink>
  <link:roleRef roleURI="http://www.pliantrx.com/role/LongtermDebtScheduleofMaturitiesofLongTermDebtDetails" xlink:type="simple" xlink:href="plrx-20230630.xsd#LongtermDebtScheduleofMaturitiesofLongTermDebtDetails"/>
  <link:calculationLink xlink:role="http://www.pliantrx.com/role/LongtermDebtScheduleofMaturitiesofLongTermDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_d7cc677a-da8b-4049-b208-6b4f4c8da1c0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebt"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_3429aa50-a8ce-4ef7-a1c3-19c0197d4ff9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LongTermDebt_d7cc677a-da8b-4049-b208-6b4f4c8da1c0" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_3429aa50-a8ce-4ef7-a1c3-19c0197d4ff9" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_plrx_LongTermDebtAccretionOfFinalPayment_a65d7bda-ff0e-4708-8ee9-5c4c6ecdab07" xlink:href="plrx-20230630.xsd#plrx_LongTermDebtAccretionOfFinalPayment"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LongTermDebt_d7cc677a-da8b-4049-b208-6b4f4c8da1c0" xlink:to="loc_plrx_LongTermDebtAccretionOfFinalPayment_a65d7bda-ff0e-4708-8ee9-5c4c6ecdab07" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnamortizedDebtIssuanceExpense_249adc01-f6e2-4862-8728-d2a6b9a9ba04" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_UnamortizedDebtIssuanceExpense"/>
    <link:calculationArc order="3" weight="-1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LongTermDebt_d7cc677a-da8b-4049-b208-6b4f4c8da1c0" xlink:to="loc_us-gaap_UnamortizedDebtIssuanceExpense_249adc01-f6e2-4862-8728-d2a6b9a9ba04" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_bb607daf-3807-4ee4-a8d6-f023e1a9e428" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:loc xlink:type="locator" xlink:label="loc_plrx_LongTermDebtMaturityAfterYearFour_8d91cf9a-7cd0-4a2f-9706-ba6bdb0b1dc8" xlink:href="plrx-20230630.xsd#plrx_LongTermDebtMaturityAfterYearFour"/>
    <link:calculationArc order="1" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DebtInstrumentCarryingAmount_bb607daf-3807-4ee4-a8d6-f023e1a9e428" xlink:to="loc_plrx_LongTermDebtMaturityAfterYearFour_8d91cf9a-7cd0-4a2f-9706-ba6bdb0b1dc8" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_738991e9-a210-40c4-bacc-777a51ece7fd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour"/>
    <link:calculationArc order="2" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DebtInstrumentCarryingAmount_bb607daf-3807-4ee4-a8d6-f023e1a9e428" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_738991e9-a210-40c4-bacc-777a51ece7fd" xlink:type="arc"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_4fa4900d-952d-4963-a828-c8966346bcb0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree"/>
    <link:calculationArc order="3" weight="1.0" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_DebtInstrumentCarryingAmount_bb607daf-3807-4ee4-a8d6-f023e1a9e428" xlink:to="loc_us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_4fa4900d-952d-4963-a828-c8966346bcb0" xlink:type="arc"/>
  </link:calculationLink>
</link:linkbase>
