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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2007-10-23</periodOfReport>

    <dateOfOriginalSubmission>2007-10-25</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001046050</issuerCik>
        <issuerName>TIMBERLAND BANCORP INC</issuerName>
        <issuerTradingSymbol>TSBK</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001251572</rptOwnerCik>
            <rptOwnerName>SAND MICHAEL R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>128 BEACON HILL DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>HOQUIAM</rptOwnerCity>
            <rptOwnerState>WA</rptOwnerState>
            <rptOwnerZipCode>98550</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President and CEO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, $0.01 par value</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2007-10-23</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>78860</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F3"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Reason for Amendment: Information was included on Table II on the reporting person's original Form 4 that was not applicable to the reported transaction, and the transaction code was incorrectly stated.  The Form 4 that was originally filed on October 25, 2007 has been restated in its entirety.</footnote>
        <footnote id="F2">Represents award of restricted stock under the Management Recognition and Development Plan (&quot;MRDP&quot;). The shares vest in equal installments over the five year period following the award date.</footnote>
        <footnote id="F3">Includes indirect ownership of 31,804 shares held by pension plan, 1,778 shares held by IRA, 1,778 shares held by wife, 2,500 shares held by children, and 1,000 shares held by MRDP Trust, does not reflect beneficial ownership of stock options reportable on Table II.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/Michael R. Sand</signatureName>
        <signatureDate>2008-02-13</signatureDate>
    </ownerSignature>
</ownershipDocument>
