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    <periodOfReport>2021-06-15</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0001594109</issuerCik>
        <issuerName>GrubHub Inc.</issuerName>
        <issuerTradingSymbol>GRUB</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
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            <rptOwnerName>Drucker Margo</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O GRUBHUB INC.</rptOwnerStreet1>
            <rptOwnerStreet2>111 W. WASHINGTON STREET, SUITE 2100</rptOwnerStreet2>
            <rptOwnerCity>CHICAGO</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60602</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
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            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Legal Officer, Secretary</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

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            </transactionCoding>
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            </transactionTimeliness>
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        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
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            <transactionDate>
                <value>2021-06-15</value>
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    <footnotes>
        <footnote id="F1">In accordance with the methodology and exchange ratio set for in the merger agreement between GrubHub Inc., Checkers Merger Sub I, Inc., Checkers Merger Sub II, Inc. and Just Eat Takeaway.com N.V. (&quot;Parent&quot;), as amended (the &quot;Merger Agreement&quot;) dated June 10, 2020, these shares were exchanged for American Depositary Shares of Parent (&quot;Parent ADSs&quot;).</footnote>
        <footnote id="F2">Each Restricted Stock Unit (&quot;RSU&quot;) represented a contingent right to receive a share of common stock or, at the option of the Compensation Committee, cash of equivalent value.</footnote>
        <footnote id="F3">In accordance with the methodology and exchange ratio set forth in the Merger Agreement, these RSUs were assumed by Parent and converted into restricted stock units with respect to Parent ADSs, subject to the previously reported applicable vesting schedules.</footnote>
        <footnote id="F4">This option, which was fully vested and exercisable, was assumed by Parent and converted, in accordance with applicable law and the methodology and exchange ratio set forth in the Merger Agreement, into an option to acquire Parent ADSs.</footnote>
        <footnote id="F5">This option, which provided for vesting 25% on February 1, 2019 with the remainder vesting ratably over the 12 consecutive quarters thereafter on May 1, August 1, November 1and February 1 of each year, was assumed by Parent and converted, in accordance with applicable law and the methodology and exchange ratio set forth in the Merger Agreement, into an option to acquire Parent ADSs subject to the foregoing vesting schedule.</footnote>
        <footnote id="F6">This option, which provided for vesting 25% on February 1, 2020 with the remainder vesting ratably over the 12 consecutive quarters thereafter on May 1, August 1, November 1 and February 1 of each year, was assumed by Parent and converted, in accordance with applicable law and the methodology and exchange ratio set forth in the Merger Agreement, into an option to acquire Parent ADSs subject to the foregoing vesting schedule.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Margo Drucker</signatureName>
        <signatureDate>2021-06-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
