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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2018-11-29</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001394319</issuerCik>
        <issuerName>Tracon Pharmaceuticals, Inc.</issuerName>
        <issuerTradingSymbol>TCON</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001733439</rptOwnerCik>
            <rptOwnerName>Puissance Cross-Border Opportunities V LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>950 THIRD AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>25TH FL</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001718140</rptOwnerCik>
            <rptOwnerName>Puissance Cross-Border Opportunities IV LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>950 THIRD AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>25TH FL</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001760460</rptOwnerCik>
            <rptOwnerName>Puissance Life Science Opportunities Fund VI</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>950 THIRD AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>FL 25</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001658437</rptOwnerCik>
            <rptOwnerName>Puissance Capital Management LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>950 THIRD AVENUE, 25TH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001695339</rptOwnerCik>
            <rptOwnerName>Puissance Capital Management (GP) LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>950 THIRD AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>25TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001695347</rptOwnerCik>
            <rptOwnerName>Puissance Capital Fund (GP) LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>950 THIRD AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>25TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001694061</rptOwnerCik>
            <rptOwnerName>Wang Theodore T</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O PUISSANCE CAPITAL MANAGEMENT LP</rptOwnerStreet1>
            <rptOwnerStreet2>950 THIRD AVENUE, 25TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2018-11-29</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4326</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>1.13</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4606094</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F4"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By funds</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2018-11-29</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4326</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>1.21</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4601768</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F4"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By funds</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4601768</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F1"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By funds</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Warrants (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>2.7</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2018-03-27</value>
            </exerciseDate>
            <expirationDate>
                <value>2024-03-27</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4601768</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4601768</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By funds</value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Consists of: 2,831,857 Shares directly owned by Puissance Cross-Border Opportunities V LLC; 1,769,911 Shares directly owned Puissance Cross-Border Opportunities IV LLC.</footnote>
        <footnote id="F2">Consists of: 2,831,857 Warrants directly owned by Puissance Cross-Border Opportunities V LLC; 1,769,911 Warrants directly owned Puissance Cross-Border Opportunities IV LLC.</footnote>
        <footnote id="F3">Puissance Capital Fund (GP) LLC serves as the managing member of Puissance Cross-Border Opportunities V LLC and Puissance Cross-Border Opportunities IV LLC and may be deemed to beneficially own these shares. Puissance Capital Management LP serves as the investment manager of Puissance Cross-Border Opportunities V LLC and Puissance Cross-Border Opportunities IV LLC and may be deemed to beneficially own these shares. Puissance Capital Management (GP) LLC serves as the general partner to Puissance Capital Management LP and may be deemed to beneficially own these shares. Theodore T. Wang serves as the managing member of Puissance Capital Fund (GP) LLC and Puissance Capital Management (GP) LLC and may be deemed to beneficially own these shares.</footnote>
        <footnote id="F4">The purchase and sale of 4,326 shares of Common Stock were under the fund Puissance Life Science Opportunities Fund VI.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Theodore T. Wang</signatureName>
        <signatureDate>2018-12-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Puissance Cross-Border Opportunities V LLC, By: Puissance Capital Fund (GP) LLC, its managing member, By: Theodore T. Wang</signatureName>
        <signatureDate>2018-12-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Puissance Cross-Border Opportunities IV LLC, By: Puissance Capital Fund (GP) LLC, its managing member, By: Theodore T. Wang</signatureName>
        <signatureDate>2018-12-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Puissance Life Science Opportunities Fund VI, By: Puissance Capital Fund (GP) LLC, its managing member, By: Theodore T. Wang</signatureName>
        <signatureDate>2018-12-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Puissance Capital Fund (GP) LLC, By: Theodore T. Wang, Managing Member</signatureName>
        <signatureDate>2018-12-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Puissance Capital Management LP, By: Puissance Capital Management (GP) LLC, its general partner, By: Theodore T. Wang, Managing Member</signatureName>
        <signatureDate>2018-12-03</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Puissance Capital Management (GP) LLC, By: Theodore Wang, Managing Member</signatureName>
        <signatureDate>2018-12-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
