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

    <schemaVersion>X0304</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2012-03-01</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001397821</issuerCik>
        <issuerName>Duff &amp; Phelps Corp</issuerName>
        <issuerTradingSymbol>DUF</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001413369</rptOwnerCik>
            <rptOwnerName>Lovell Minnick Partners LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>150 N. RADNOR CHESTER ROAD, SUITE A200</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>RADNOR</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>19807</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Duff and Phelps Acquisitions, LLC New Class A Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2012-03-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1390602</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>13.38</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F1"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A common stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1390602</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2224962</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Lovell Minnick Equity Partners LP (&quot;LMEP&quot;), an affiliate of Lovell Minnick Partners LLC (&quot;LMP&quot;), holds New Class A Units in Duff and Phelps Acquisitions LLC (&quot;DPA&quot;), an affiliate of Duff and Phelps Corporation (&quot;DPC&quot;).  Pursuant to an exchange agreement entered into an October 3, 2007 in connection with the closing of the initial public offering of DPC (the &quot;IPO&quot;), holders of New Class A Units of DPA issued in connection with the reorganization of DPA immediately prior to the consummation of the IPO (the &quot;Reorganization&quot;) may exchange their New Class A Units for Class A Common stock of DPC on a one-for-one basis up to four times each year, subject to the vesting, minimum retained ownership requirements and transfer restrictions and customary conversion rate adjustments for splits, unit distributions and reclassifications contained in the exchange agreement.</footnote>
        <footnote id="F2">On March 1, 2012, DPA redeemed 1,390,602 of the New Class A Units of DPA from LMEP for a price per share of $13.38.</footnote>
        <footnote id="F3">LMEP owns New Class A Units of DPA.  LMEP is controlled by its sole general partner, Lovell Minnick Equity Advisors LLC  (&quot;LMEA&quot;), and LMEA is controlled by its sole managing member, LMP.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Jennings J. Newcom. Managing Director</signatureName>
        <signatureDate>2012-03-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
