

<!--XBRL Document Created with Wdesk from Workiva, formerly WebFilings-->
<!-- -->
<linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <roleRef roleURI="http://www.flex-pharma.com/role/AccruedExpensesAndOtherCurrentLiabilities" xlink:href="flks-20150331.xsd#AccruedExpensesAndOtherCurrentLiabilities" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/AccruedExpensesAndOtherCurrentLiabilitiesDetails" xlink:href="flks-20150331.xsd#AccruedExpensesAndOtherCurrentLiabilitiesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/AccruedExpensesAndOtherCurrentLiabilitiesTables" xlink:href="flks-20150331.xsd#AccruedExpensesAndOtherCurrentLiabilitiesTables" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/CommonStock" xlink:href="flks-20150331.xsd#CommonStock" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/CommonStockCommonStockTables" xlink:href="flks-20150331.xsd#CommonStockCommonStockTables" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/CommonStockNarrativeDetails" xlink:href="flks-20150331.xsd#CommonStockNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/CommonStockRestrictedCommonStockActivityDetails" xlink:href="flks-20150331.xsd#CommonStockRestrictedCommonStockActivityDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/CondensedConsolidatedBalanceSheetUnaudited" xlink:href="flks-20150331.xsd#CondensedConsolidatedBalanceSheetUnaudited" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/CondensedConsolidatedBalanceSheetUnauditedParenthetical" xlink:href="flks-20150331.xsd#CondensedConsolidatedBalanceSheetUnauditedParenthetical" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/CondensedConsolidatedStatementsOfCashFlowsUnaudited" xlink:href="flks-20150331.xsd#CondensedConsolidatedStatementsOfCashFlowsUnaudited" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/CondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited" xlink:href="flks-20150331.xsd#CondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/DocumentAndEntityInformationDocumentAndEntityInformation" xlink:href="flks-20150331.xsd#DocumentAndEntityInformationDocumentAndEntityInformation" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/IncomeTaxes" xlink:href="flks-20150331.xsd#IncomeTaxes" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/NetLossPerShare" xlink:href="flks-20150331.xsd#NetLossPerShare" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/NetLossPerShareDetails" xlink:href="flks-20150331.xsd#NetLossPerShareDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/NetLossPerShareTables" xlink:href="flks-20150331.xsd#NetLossPerShareTables" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/OrganizationAndOperations" xlink:href="flks-20150331.xsd#OrganizationAndOperations" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/OrganizationAndOperationsDetails" xlink:href="flks-20150331.xsd#OrganizationAndOperationsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/StockBasedCompensation" xlink:href="flks-20150331.xsd#StockBasedCompensation" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/StockBasedCompensationNarrativeDetails" xlink:href="flks-20150331.xsd#StockBasedCompensationNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/StockBasedCompensationSummaryOfStockBasedCompensationExpenseDetails" xlink:href="flks-20150331.xsd#StockBasedCompensationSummaryOfStockBasedCompensationExpenseDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/StockBasedCompensationSummaryOfStockOptionActivityDetails" xlink:href="flks-20150331.xsd#StockBasedCompensationSummaryOfStockOptionActivityDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/StockBasedCompensationTables" xlink:href="flks-20150331.xsd#StockBasedCompensationTables" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncements" xlink:href="flks-20150331.xsd#SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncements" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsNarrativeDetails" xlink:href="flks-20150331.xsd#SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsNarrativeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.flex-pharma.com/role/SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsPolicies" xlink:href="flks-20150331.xsd#SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsPolicies" xlink:type="simple" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/AccruedExpensesAndOtherCurrentLiabilities" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/AccruedExpensesAndOtherCurrentLiabilitiesDetails" xlink:type="extended">
    <loc xlink:href="flks-20150331.xsd#flks_AccruedExpensesAndOtherCurrentLiabilities" xlink:label="loc_flks_AccruedExpensesAndOtherCurrentLiabilities_290b1c63-9c29-11e4-a13c-22000a9f3af2" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_EmployeeRelatedLiabilitiesCurrent" xlink:label="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_d69c5cc5-fc70-31a7-c2b1-924eb363b75b" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_flks_AccruedExpensesAndOtherCurrentLiabilities_290b1c63-9c29-11e4-a13c-22000a9f3af2" xlink:to="loc_us-gaap_EmployeeRelatedLiabilitiesCurrent_d69c5cc5-fc70-31a7-c2b1-924eb363b75b" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AccruedMarketingCostsCurrent" xlink:label="loc_us-gaap_AccruedMarketingCostsCurrent_53fe0802-e552-e21f-68c7-b9003178737a" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_flks_AccruedExpensesAndOtherCurrentLiabilities_290b1c63-9c29-11e4-a13c-22000a9f3af2" xlink:to="loc_us-gaap_AccruedMarketingCostsCurrent_53fe0802-e552-e21f-68c7-b9003178737a" xlink:type="arc" />
    <loc xlink:href="flks-20150331.xsd#flks_AccruedResearchAndDevelopmentExpenseCurrent" xlink:label="loc_flks_AccruedResearchAndDevelopmentExpenseCurrent_0ab42ca5-bcaf-4748-e785-ca6ed74dc429" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_flks_AccruedExpensesAndOtherCurrentLiabilities_290b1c63-9c29-11e4-a13c-22000a9f3af2" xlink:to="loc_flks_AccruedResearchAndDevelopmentExpenseCurrent_0ab42ca5-bcaf-4748-e785-ca6ed74dc429" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AccruedProfessionalFeesCurrent" xlink:label="loc_us-gaap_AccruedProfessionalFeesCurrent_28c626c7-9023-e30f-2e48-0f4dd115d912" xlink:type="locator" />
    <calculationArc order="4" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_flks_AccruedExpensesAndOtherCurrentLiabilities_290b1c63-9c29-11e4-a13c-22000a9f3af2" xlink:to="loc_us-gaap_AccruedProfessionalFeesCurrent_28c626c7-9023-e30f-2e48-0f4dd115d912" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_OtherAccruedLiabilitiesCurrent" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesCurrent_46c5e103-584b-b600-2852-4201435cc29f" xlink:type="locator" />
    <calculationArc order="5" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_flks_AccruedExpensesAndOtherCurrentLiabilities_290b1c63-9c29-11e4-a13c-22000a9f3af2" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesCurrent_46c5e103-584b-b600-2852-4201435cc29f" xlink:type="arc" />
    <loc xlink:href="flks-20150331.xsd#flks_DeferredIPOIssuanceCostCurrent" xlink:label="loc_flks_DeferredIPOIssuanceCostCurrent_60ec0030-bf07-05ec-8028-ca6ed74dffa2" xlink:type="locator" />
    <calculationArc order="6" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_flks_AccruedExpensesAndOtherCurrentLiabilities_290b1c63-9c29-11e4-a13c-22000a9f3af2" xlink:to="loc_flks_DeferredIPOIssuanceCostCurrent_60ec0030-bf07-05ec-8028-ca6ed74dffa2" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.flex-pharma.com/role/AccruedExpensesAndOtherCurrentLiabilitiesTables" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/CommonStock" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/CommonStockCommonStockTables" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/CommonStockNarrativeDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/CommonStockRestrictedCommonStockActivityDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/CondensedConsolidatedBalanceSheetUnaudited" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_b517a4f1-4597-b094-2608-75af660328e1" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="loc_us-gaap_AssetsCurrent_67f49e84-05fd-4b0b-ae5a-e9913b97cea2" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_b517a4f1-4597-b094-2608-75af660328e1" xlink:to="loc_us-gaap_AssetsCurrent_67f49e84-05fd-4b0b-ae5a-e9913b97cea2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_Cash" xlink:label="loc_us-gaap_Cash_ed1351d7-08ed-47ff-642b-430da354f5e2" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_67f49e84-05fd-4b0b-ae5a-e9913b97cea2" xlink:to="loc_us-gaap_Cash_ed1351d7-08ed-47ff-642b-430da354f5e2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_3227d5e9-cb9d-fda7-e599-c6fb89b5e07a" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_AssetsCurrent_67f49e84-05fd-4b0b-ae5a-e9913b97cea2" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_3227d5e9-cb9d-fda7-e599-c6fb89b5e07a" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_a1eaafaf-055b-e423-85ef-4424fb2ef4e4" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_b517a4f1-4597-b094-2608-75af660328e1" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_a1eaafaf-055b-e423-85ef-4424fb2ef4e4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DeferredFinanceCostsNoncurrentNet" xlink:label="loc_us-gaap_DeferredFinanceCostsNoncurrentNet_24a9334e-39d3-bf69-8cc1-15212ef72c7b" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_b517a4f1-4597-b094-2608-75af660328e1" xlink:to="loc_us-gaap_DeferredFinanceCostsNoncurrentNet_24a9334e-39d3-bf69-8cc1-15212ef72c7b" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DeferredTaxAssetsNetNoncurrent" xlink:label="loc_us-gaap_DeferredTaxAssetsNetNoncurrent_845254ea-8acf-3ce8-9356-c6d0b076c3a8" xlink:type="locator" />
    <calculationArc order="4" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_b517a4f1-4597-b094-2608-75af660328e1" xlink:to="loc_us-gaap_DeferredTaxAssetsNetNoncurrent_845254ea-8acf-3ce8-9356-c6d0b076c3a8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_4599c23a-11f0-4277-ea32-9886d26f8792" xlink:type="locator" />
    <calculationArc order="5" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_b517a4f1-4597-b094-2608-75af660328e1" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_4599c23a-11f0-4277-ea32-9886d26f8792" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsNoncurrent" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsNoncurrent_913601c5-bb02-9f7f-1683-87bdfa12cca4" xlink:type="locator" />
    <calculationArc order="6" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Assets_b517a4f1-4597-b094-2608-75af660328e1" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsNoncurrent_913601c5-bb02-9f7f-1683-87bdfa12cca4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity_26e56c7a-24ab-e869-809a-0509ccbe86d9" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PreferredStockValue" xlink:label="loc_us-gaap_PreferredStockValue_9fd7dfd7-596e-4c7f-4077-abbf8130d157" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_26e56c7a-24ab-e869-809a-0509ccbe86d9" xlink:to="loc_us-gaap_PreferredStockValue_9fd7dfd7-596e-4c7f-4077-abbf8130d157" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CommonStockValue" xlink:label="loc_us-gaap_CommonStockValue_ffd09989-75a8-4713-beb0-21bebb3561d6" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_26e56c7a-24ab-e869-809a-0509ccbe86d9" xlink:to="loc_us-gaap_CommonStockValue_ffd09989-75a8-4713-beb0-21bebb3561d6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="loc_us-gaap_AdditionalPaidInCapital_dcbd5d14-4ec6-06fe-e5c1-a41efced6761" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_26e56c7a-24ab-e869-809a-0509ccbe86d9" xlink:to="loc_us-gaap_AdditionalPaidInCapital_dcbd5d14-4ec6-06fe-e5c1-a41efced6761" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_440a13e9-e4dc-f397-4d0d-27daacd44483" xlink:type="locator" />
    <calculationArc order="4" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_StockholdersEquity_26e56c7a-24ab-e869-809a-0509ccbe86d9" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_440a13e9-e4dc-f397-4d0d-27daacd44483" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_Liabilities" xlink:label="loc_us-gaap_Liabilities_16ce0436-3b82-55c5-d896-5cba4c9023bd" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="loc_us-gaap_LiabilitiesCurrent_1477e02d-b6d8-3df6-e715-8364fedce6d9" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_16ce0436-3b82-55c5-d896-5cba4c9023bd" xlink:to="loc_us-gaap_LiabilitiesCurrent_1477e02d-b6d8-3df6-e715-8364fedce6d9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_AccountsPayableCurrent" xlink:label="loc_us-gaap_AccountsPayableCurrent_bd7b63fa-09ae-1100-16fe-5ac027208548" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesCurrent_1477e02d-b6d8-3df6-e715-8364fedce6d9" xlink:to="loc_us-gaap_AccountsPayableCurrent_bd7b63fa-09ae-1100-16fe-5ac027208548" xlink:type="arc" />
    <loc xlink:href="flks-20150331.xsd#flks_AccruedExpensesAndOtherCurrentLiabilities" xlink:label="loc_flks_AccruedExpensesAndOtherCurrentLiabilities_290b1c63-9c29-11e4-a13c-22000a9f3af2" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesCurrent_1477e02d-b6d8-3df6-e715-8364fedce6d9" xlink:to="loc_flks_AccruedExpensesAndOtherCurrentLiabilities_290b1c63-9c29-11e4-a13c-22000a9f3af2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DeferredTaxLiabilitiesCurrent" xlink:label="loc_us-gaap_DeferredTaxLiabilitiesCurrent_712a848e-6493-088e-8a82-029610cac2c5" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesCurrent_1477e02d-b6d8-3df6-e715-8364fedce6d9" xlink:to="loc_us-gaap_DeferredTaxLiabilitiesCurrent_712a848e-6493-088e-8a82-029610cac2c5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DeferredRentCreditCurrent" xlink:label="loc_us-gaap_DeferredRentCreditCurrent_23362b02-01cb-51af-a2d0-3af1739fa1db" xlink:type="locator" />
    <calculationArc order="4" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_LiabilitiesCurrent_1477e02d-b6d8-3df6-e715-8364fedce6d9" xlink:to="loc_us-gaap_DeferredRentCreditCurrent_23362b02-01cb-51af-a2d0-3af1739fa1db" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_DeferredRentCreditNoncurrent" xlink:label="loc_us-gaap_DeferredRentCreditNoncurrent_55393c1a-fc24-e579-ffe3-04ec8ee0f328" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_16ce0436-3b82-55c5-d896-5cba4c9023bd" xlink:to="loc_us-gaap_DeferredRentCreditNoncurrent_55393c1a-fc24-e579-ffe3-04ec8ee0f328" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_f7fce5cd-2d53-a8b3-a485-6d0f3635b8fe" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_Liabilities_16ce0436-3b82-55c5-d896-5cba4c9023bd" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_f7fce5cd-2d53-a8b3-a485-6d0f3635b8fe" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.flex-pharma.com/role/CondensedConsolidatedBalanceSheetUnauditedParenthetical" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/CondensedConsolidatedStatementsOfCashFlowsUnaudited" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_CashPeriodIncreaseDecrease" xlink:label="loc_us-gaap_CashPeriodIncreaseDecrease_87378abe-107c-23f0-f640-84d54ed2d5e9" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_6d7b73b6-0db7-23f7-377e-417fa8fc8e27" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_CashPeriodIncreaseDecrease_87378abe-107c-23f0-f640-84d54ed2d5e9" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_6d7b73b6-0db7-23f7-377e-417fa8fc8e27" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_fb013d5f-7e0c-1a40-5a42-42bd8c3a1d51" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_CashPeriodIncreaseDecrease_87378abe-107c-23f0-f640-84d54ed2d5e9" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_fb013d5f-7e0c-1a40-5a42-42bd8c3a1d51" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_37181af6-e562-cefc-f2b6-8490ea2c3e04" xlink:type="locator" />
    <calculationArc order="1" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_fb013d5f-7e0c-1a40-5a42-42bd8c3a1d51" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_37181af6-e562-cefc-f2b6-8490ea2c3e04" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_b6b5c2f7-2ab7-a264-6d06-119dda52768c" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_CashPeriodIncreaseDecrease_87378abe-107c-23f0-f640-84d54ed2d5e9" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_b6b5c2f7-2ab7-a264-6d06-119dda52768c" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_faecc408-4bea-6e13-83bd-71b4c2ddf64c" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_b6b5c2f7-2ab7-a264-6d06-119dda52768c" xlink:to="loc_us-gaap_NetIncomeLoss_faecc408-4bea-6e13-83bd-71b4c2ddf64c" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_Depreciation" xlink:label="loc_us-gaap_Depreciation_296ac298-3acc-b888-34a0-99e6da446889" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_b6b5c2f7-2ab7-a264-6d06-119dda52768c" xlink:to="loc_us-gaap_Depreciation_296ac298-3acc-b888-34a0-99e6da446889" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:label="loc_us-gaap_ShareBasedCompensation_aa7a0bc5-86c6-13a8-3676-9960bad8007f" xlink:type="locator" />
    <calculationArc order="3" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_b6b5c2f7-2ab7-a264-6d06-119dda52768c" xlink:to="loc_us-gaap_ShareBasedCompensation_aa7a0bc5-86c6-13a8-3676-9960bad8007f" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncreaseDecreaseInRestrictedCashForOperatingActivities" xlink:label="loc_us-gaap_IncreaseDecreaseInRestrictedCashForOperatingActivities_b24a1c7f-fa2c-6aba-5e29-c2fecacee68f" xlink:type="locator" />
    <calculationArc order="4" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_b6b5c2f7-2ab7-a264-6d06-119dda52768c" xlink:to="loc_us-gaap_IncreaseDecreaseInRestrictedCashForOperatingActivities_b24a1c7f-fa2c-6aba-5e29-c2fecacee68f" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_07d730ea-b32b-956c-677e-cf5b73c388b0" xlink:type="locator" />
    <calculationArc order="5" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_b6b5c2f7-2ab7-a264-6d06-119dda52768c" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_07d730ea-b32b-956c-677e-cf5b73c388b0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncreaseDecreaseInOtherNoncurrentAssets" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_61010cf2-f381-68a2-d0b7-2785316c9e09" xlink:type="locator" />
    <calculationArc order="6" weight="-1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_b6b5c2f7-2ab7-a264-6d06-119dda52768c" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_61010cf2-f381-68a2-d0b7-2785316c9e09" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsPayable" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_b9fb8522-752c-3209-8cca-60e64f420ad5" xlink:type="locator" />
    <calculationArc order="7" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_b6b5c2f7-2ab7-a264-6d06-119dda52768c" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_b9fb8522-752c-3209-8cca-60e64f420ad5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_5cb9a7e8-dd26-27c7-9313-c478703eadea" xlink:type="locator" />
    <calculationArc order="8" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_b6b5c2f7-2ab7-a264-6d06-119dda52768c" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_5cb9a7e8-dd26-27c7-9313-c478703eadea" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncreaseDecreaseInDeferredLiabilities" xlink:label="loc_us-gaap_IncreaseDecreaseInDeferredLiabilities_2a8737e7-4843-3e79-f5bc-ba4bec765cee" xlink:type="locator" />
    <calculationArc order="9" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_b6b5c2f7-2ab7-a264-6d06-119dda52768c" xlink:to="loc_us-gaap_IncreaseDecreaseInDeferredLiabilities_2a8737e7-4843-3e79-f5bc-ba4bec765cee" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.flex-pharma.com/role/CondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_OperatingExpenses" xlink:label="loc_us-gaap_OperatingExpenses_ee2bd36d-150a-7303-38c4-eb755f792210" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_ResearchAndDevelopmentExpense" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_7d1bc05d-33ee-c009-4533-b70ee0a74dc9" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingExpenses_ee2bd36d-150a-7303-38c4-eb755f792210" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_7d1bc05d-33ee-c009-4533-b70ee0a74dc9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_GeneralAndAdministrativeExpense" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_7c6d12de-ee49-8fea-ba36-2f44ccb8dae4" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_OperatingExpenses_ee2bd36d-150a-7303-38c4-eb755f792210" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_7c6d12de-ee49-8fea-ba36-2f44ccb8dae4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaap_NetIncomeLoss_faecc408-4bea-6e13-83bd-71b4c2ddf64c" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_cc64ed8f-51e0-4a92-b0c8-acb3ad13358b" xlink:type="locator" />
    <calculationArc order="1" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetIncomeLoss_faecc408-4bea-6e13-83bd-71b4c2ddf64c" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_cc64ed8f-51e0-4a92-b0c8-acb3ad13358b" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2014/elts/us-gaap-2014-01-31.xsd#us-gaap_InterestIncomeOperating" xlink:label="loc_us-gaap_InterestIncomeOperating_e7baa765-e731-d3bc-1056-f5623f4a4c01" xlink:type="locator" />
    <calculationArc order="2" weight="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/summation-item" xlink:from="loc_us-gaap_NetIncomeLoss_faecc408-4bea-6e13-83bd-71b4c2ddf64c" xlink:to="loc_us-gaap_InterestIncomeOperating_e7baa765-e731-d3bc-1056-f5623f4a4c01" xlink:type="arc" />
  </calculationLink>
  <calculationLink xlink:role="http://www.flex-pharma.com/role/DocumentAndEntityInformationDocumentAndEntityInformation" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/IncomeTaxes" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/NetLossPerShare" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/NetLossPerShareDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/NetLossPerShareTables" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/OrganizationAndOperations" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/OrganizationAndOperationsDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/StockBasedCompensation" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/StockBasedCompensationNarrativeDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/StockBasedCompensationSummaryOfStockBasedCompensationExpenseDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/StockBasedCompensationSummaryOfStockOptionActivityDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/StockBasedCompensationTables" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncements" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsNarrativeDetails" xlink:type="extended" />
  <calculationLink xlink:role="http://www.flex-pharma.com/role/SummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsPolicies" xlink:type="extended" />
</linkbase>





