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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2015-11-18</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001501364</issuerCik>
        <issuerName>United Financial Bancorp, Inc.</issuerName>
        <issuerTradingSymbol>UBNK</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001325607</rptOwnerCik>
            <rptOwnerName>Ross Kevin E</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>UNITED FINANCIAL BANCORP, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>45 GLASTONBURY BLVD.</rptOwnerStreet2>
            <rptOwnerCity>GLASTONBURY</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06033</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-11-18</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2209</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>34999</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>Stock Options</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>8.66</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2009-06-19</value>
            </exerciseDate>
            <expirationDate>
                <value>2018-06-19</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>27617</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>27617</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F5"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Options</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>9.17</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2007-08-17</value>
            </exerciseDate>
            <expirationDate>
                <value>2016-08-17</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>28743</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>28743</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F6"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Includes shares of restricted stock that are 100% vested as of April 30, 2014.</footnote>
        <footnote id="F2">Pursuant to the Agreement and Plan of Merger, dated November 14, 2013, each share of United Financial Bancorp, Inc. was exchanged for 1.3472 shares of Rockville Financial, Inc. At legal close, Rockville Financial, Inc. changed its name to United Financial Bancorp, Inc. in connection with the merger of United Financial Bancorp, Inc. into Rockville Financial, Inc.</footnote>
        <footnote id="F3">Includes 1,820 shares of Restricted Stock granted pursuant to the Rockville Financial, Inc.'s 2012 Stock Incentive Plan and shall vest on the first annual anniversary of the grant date.</footnote>
        <footnote id="F4">Transaction represents 2,209 shares of Restricted Stock granted pursuant to the United Financial Bancorp, Inc. 2015 Omnibus Stock Incentive Plan and shall vest on the first annual anniversary of the grant date.</footnote>
        <footnote id="F5">Options to purchase shares of common stock are 100% vested and also includes an equal number of stock appreciation rights.</footnote>
        <footnote id="F6">Options to purchase shares of common stock are 100% vested</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Marliese L. Shaw by POA</signatureName>
        <signatureDate>2015-11-20</signatureDate>
    </ownerSignature>
</ownershipDocument>
