SBLK: Pappa Milena Maria reported buying shares

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

    <schemaVersion>X0609</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2026-09-15</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001386716</issuerCik>
        <issuerName>Star Bulk Carriers Corp.</issuerName>
        <issuerTradingSymbol>SBLK</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0002113812</rptOwnerCik>
            <rptOwnerName>Pappa Milena Maria</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerNonUSAddressFlag>true</rptOwnerNonUSAddressFlag>
            <rptOwnerStreet1>40 AG KONSTANTINOU STREET</rptOwnerStreet1>
            <rptOwnerStreet2>MAROUSI</rptOwnerStreet2>
            <rptOwnerCity>ATHENS</rptOwnerCity>
            <rptOwnerNonUSStateTerritory></rptOwnerNonUSStateTerritory>
            <rptOwnerCountry>J3</rptOwnerCountry>
            <rptOwnerZipCode>15124</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Shares par value $0.01 per share</value>
            </securityTitle>
            <transactionDate>
                <value>2026-09-15</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>74400</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>28.27</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3167074</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F1"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>by corporations</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Shares par value $0.01 per share</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">These shares are held by 3 corporations in which the reporting person holds 100% of the economic interest and over which the reporting person has investment control.</footnote>
    </footnotes>

    <remarks>Participation in the public offering undertaken by Star Bulk Carriers Corp in Greece, following its dual listing on Euronext Athens, pursuant to which the reporting person subscribed to 74,400 new common shares, through an entity controlled by her, at the offering price of EUR 24.50 per share (or equivalent to $ 28.27).</remarks>

    <ownerSignature>
        <signatureName>Milena Maria Pappa</signatureName>
        <signatureDate>2026-09-17</signatureDate>
    </ownerSignature>
</ownershipDocument>