<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2017-05-12</periodOfReport>

    <issuer>
        <issuerCik>0001436425</issuerCik>
        <issuerName>HOME BANCORP, INC.</issuerName>
        <issuerTradingSymbol>HBCP</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001446487</rptOwnerCik>
            <rptOwnerName>BLANCHET PAUL J. III</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O HOME BANCORP, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>503 KALISTE SALOOM ROAD</rptOwnerStreet2>
            <rptOwnerCity>LAFAYETTE</rptOwnerCity>
            <rptOwnerState>LA</rptOwnerState>
            <rptOwnerZipCode>70598</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2017-05-12</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>420</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>60620</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Employee Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>11.45</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <value>2019-05-12</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>10980</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10980</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Includes 12,000 shares held jointly with reporting person's spouse.</footnote>
        <footnote id="F2">Includes the grant of 800 restricted stock units pursuant to the Issuer's 2014 Incentive Plan that vest in equal installments at the rate of 20% per year commencing on May 12, 2017 and that may be settled only in shares of the Issuer's common stock.</footnote>
        <footnote id="F3">Includes the grant of 900 restricted stock units pursuant to the Issuer's 2014 Incentive Plan that vest in equal installments at the rate of 20% per year commencing on May 12, 2016 and that may be settled only in shares of the Issuer's common stock.</footnote>
        <footnote id="F4">Represents the grant of 420 restricted stock units pursuant to the Issuer's 2014 Incentive Plan that vest in equal installments at the rate of 20% per year commencing on May 12, 2018 and that may be settled only in shares of the Issuer's common stock.</footnote>
        <footnote id="F5">The options are fully vested; they became exercisable in five equal annual installments beginning on May 12, 2010.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Paul J. Blanchet, III</signatureName>
        <signatureDate>2017-05-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
