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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-04-06</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001170593</issuerCik>
        <issuerName>PRIMUS GUARANTY LTD</issuerName>
        <issuerTradingSymbol>PRS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001164098</rptOwnerCik>
            <rptOwnerName>TRANSAMERICA LIFE INSURANCE CO</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O AEGON USA INVESTMENT MANAGEMENT LLC</rptOwnerStreet1>
            <rptOwnerStreet2>4333 EDGEWOOD ROAD N.E.</rptOwnerStreet2>
            <rptOwnerCity>CEDAR RAPIDS</rptOwnerCity>
            <rptOwnerState>IA</rptOwnerState>
            <rptOwnerZipCode>52499-5335</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Deferred Shares</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2006-04-06</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>336</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>11.15</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6192</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Includes 336 Deferred Shares issued to Thomas Hartlage, as a non-employee director of Primus Guaranty, Ltd., under the Primus Guaranty, Ltd. 2004 Stock Incentive Plan on January 3, 2005 based on the market closing price of $11.15 per common share on March 31, 2006.  The Deferred Shares become payable upon completion of Mr. Hartlages board service.  Mr. Hartlage ceded beneficial ownership of such shares to Transamerica Life Insurance Company.</footnote>
        <footnote id="F2">Excludes 5,582,585 Common Shares, par value $.08 per share, directly beneficially owned by Transamerica Life Insurance Company.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>R. Michael Slaven</signatureName>
        <signatureDate>2006-04-10</signatureDate>
    </ownerSignature>
</ownershipDocument>
