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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2013-09-18</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001490660</issuerCik>
        <issuerName>Marketo, Inc.</issuerName>
        <issuerTradingSymbol>MKTO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001576722</rptOwnerCik>
            <rptOwnerName>STORM VENTURE ASSOCIATES III, L.L.C.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O STORM VENTURES</rptOwnerStreet1>
            <rptOwnerStreet2>2440 SAND HILL ROAD, SUITE 301</rptOwnerStreet2>
            <rptOwnerCity>MENLO PARK</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94025</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001313016</rptOwnerCik>
            <rptOwnerName>STORM VENTURES FUND III LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O STORM VENTURES</rptOwnerStreet1>
            <rptOwnerStreet2>2440 SAND HILL ROAD, SUITE 301</rptOwnerStreet2>
            <rptOwnerCity>MENLO PARK</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94025</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001326513</rptOwnerCik>
            <rptOwnerName>STORM VENTURES AFFILIATES FUND III LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O STORM VENTURES</rptOwnerStreet1>
            <rptOwnerStreet2>2440 SAND HILL ROAD, SUITE 301</rptOwnerStreet2>
            <rptOwnerCity>MENLO PARK</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94025</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001312946</rptOwnerCik>
            <rptOwnerName>STORM VENTURES PRINCIPALS FUND III</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O STORM VENTURES</rptOwnerStreet1>
            <rptOwnerStreet2>2440 SAND HILL ROAD, SUITE 301</rptOwnerStreet2>
            <rptOwnerCity>MENLO PARK</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94025</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2013-09-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1001909</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>33.9913</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3685450</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnotes</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2013-09-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>54803</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>33.9913</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>201586</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnotes</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2013-09-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>31038</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>33.9913</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>114170</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnotes</value>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The shares are held directly by Storm Ventures Fund III, L.P. (&quot;SV III&quot;).</footnote>
        <footnote id="F2">The shares are held directly by Storm Ventures Affiliates Fund III, L.P. (&quot;SVA III&quot;).</footnote>
        <footnote id="F3">The shares are held directly by Storm Ventures Principals Fund III, L.L.C. (&quot;SVP III&quot;).</footnote>
        <footnote id="F4">Storm Venture Associates III, L.L.C. (&quot;SVA LLC&quot;) is the general partner of SV III and SVA III and the managing member of SVP III. Ryan Floyd, M. Alex Mendez, Tae Hea Nahm and Sanjay Subhedar are the managing members of SVA LLC. Ryan Floyd, M. Alex Mendez, Tae Hea Nahm and Sanjay Subhedar as the managing members of SVA LLC may be deemed to share voting and investment power with respect to the shares held by SV III, SVA III and SVP III. Each of the managing directors disclaims beneficial ownership of the shares reported herein, except to the extent of his respective pecuniary interest therein.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Tae Hea Nahm, a Managing Member of Storm Venture Associates III, L.L.C.</signatureName>
        <signatureDate>2013-09-18</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Tae Hea Nahm, a Managing Member of Storm Venture Associates III, L.L.C., the General Partner of Storm Ventures Fund III, L.P.</signatureName>
        <signatureDate>2013-09-18</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Tae Hea Nahm, a Managing Member of Storm Venture Associates III, L.L.C., the General Partner of Storm Ventures Affiliates Fund III, L.P.</signatureName>
        <signatureDate>2013-09-18</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Tae Hea Nahm, a Managing Member of Storm Venture Associates III, L.L.C., the Managing Member of Storm Ventures Principals Fund III, L.L.C.</signatureName>
        <signatureDate>2013-09-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
