<SUBMISSION>
<ACCESSION-NUMBER>0001222579-03-000001
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20030701
<FILING-DATE>20030703
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>PYLE MICHAEL R
<CIK>0001222579
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>001-11859
<FILM-NUMBER>03774360
</FILING-VALUES>
<MAIL-ADDRESS>
<STREET1>C/O PEGASYSTEMS INC
<STREET2>101 MAIN STREET
<CITY>CAMBRIGE
<STATE>MA
<ZIP>02142
</MAIL-ADDRESS>
</REPORTING-OWNER>
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>PEGASYSTEMS INC
<CIK>0001013857
<ASSIGNED-SIC>7374
<IRS-NUMBER>042787865
<STATE-OF-INCORPORATION>MA
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>101 MAIN ST
<CITY>CAMBRIDGE
<STATE>MA
<ZIP>02142-1590
<PHONE>6173749600
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>101 MAIN ST
<CITY>CAMBRIDGE
<STATE>MA
<ZIP>02142-1590
</MAIL-ADDRESS>
</ISSUER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>

<ownershipDocument>

    <documentType>4</documentType>

    <periodOfReport>2003-07-01</periodOfReport>


    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001013857</issuerCik>
        <issuerName>PEGASYSTEMS INC</issuerName>
        <issuerTradingSymbol>PEGA</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001222579</rptOwnerCik>
            <rptOwnerName>PYLE MICHAEL R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>SVP of Product Development</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeSecurity>
        <securityTitle>
            <value>Common Stock</value>
        </securityTitle>
        <transactionDate>
            <value>2003-07-01</value>
        </transactionDate>
        <transactionCoding>
            <transactionFormType>4</transactionFormType>
            <transactionCode>M</transactionCode>
            <equitySwapInvolved>0</equitySwapInvolved>
        </transactionCoding>
        <transactionTimeliness>
            <value></value>
        </transactionTimeliness>
        <transactionAmounts>
            <transactionShares>
                <value>20000</value>
            </transactionShares>
            <transactionValue>
                <value>0.3267</value>
            </transactionValue>
            <transactionAcquiredDisposedCode>
                <value>A</value>
            </transactionAcquiredDisposedCode>
        </transactionAmounts>
        <postTransactionAmounts>
            <sharesOwnedFollowingTransaction>
                <value>0</value>
            </sharesOwnedFollowingTransaction>
        </postTransactionAmounts>
        <ownershipNature>
            <directOrIndirectOwnership>
                <value>D</value>
            </directOrIndirectOwnership>
        </ownershipNature>
    </nonDerivativeSecurity>

    <nonDerivativeSecurity>
        <securityTitle>
            <value>Common Stock</value>
        </securityTitle>
        <transactionDate>
            <value>2003-07-01</value>
        </transactionDate>
        <transactionCoding>
            <transactionFormType>4</transactionFormType>
            <transactionCode>S</transactionCode>
            <equitySwapInvolved>0</equitySwapInvolved>
        </transactionCoding>
        <transactionTimeliness>
            <value></value>
        </transactionTimeliness>
        <transactionAmounts>
            <transactionShares>
                <value>10000</value>
            </transactionShares>
            <transactionValue>
                <value>7.5119</value>
            </transactionValue>
            <transactionAcquiredDisposedCode>
                <value>D</value>
            </transactionAcquiredDisposedCode>
        </transactionAmounts>
        <postTransactionAmounts>
            <sharesOwnedFollowingTransaction>
                <value>10000</value>
            </sharesOwnedFollowingTransaction>
        </postTransactionAmounts>
        <ownershipNature>
            <directOrIndirectOwnership>
                <value>D</value>
            </directOrIndirectOwnership>
        </ownershipNature>
    </nonDerivativeSecurity>

    <derivativeSecurity>
        <securityTitle>
            <value>Stock Option</value>
        </securityTitle>
        <conversionOrExercisePrice>
            <value>0.3267</value>
        </conversionOrExercisePrice>
        <transactionDate>
            <value>2003-07-01</value>
        </transactionDate>
        <transactionCoding>
            <transactionFormType>4</transactionFormType>
            <transactionCode>M</transactionCode>
            <equitySwapInvolved>0</equitySwapInvolved>
        </transactionCoding>
        <transactionTimeliness>
            <value></value>
        </transactionTimeliness>
        <transactionAmounts>
            <transactionShares>
                <value>20000</value>
                <footnoteId id="F1"/>
            </transactionShares>
            <transactionValue>
                <value>0</value>
            </transactionValue>
            <transactionAcquiredDisposedCode>
                <value>D</value>
            </transactionAcquiredDisposedCode>
        </transactionAmounts>
        <exerciseDate>
            <value>1999-12-29</value>
        </exerciseDate>
        <expirationDate>
            <value>2004-12-29</value>
        </expirationDate>
        <underlyingSecurity>
            <underlyingSecurityTitle>
                <value>Common</value>
            </underlyingSecurityTitle>
            <underlyingSecurityShares>
                <value>216000</value>
            </underlyingSecurityShares>
        </underlyingSecurity>
        <postTransactionAmounts>
            <sharesOwnedFollowingTransaction>
                <value>25100</value>
            </sharesOwnedFollowingTransaction>
        </postTransactionAmounts>
        <ownershipNature>
            <directOrIndirectOwnership>
                <value>D</value>
            </directOrIndirectOwnership>
        </ownershipNature>
    </derivativeSecurity>

    <footnotes>
        <footnote id="F1">20,000 shares of Common Stock were exercised from a total grant of 216,000 shares of Common Stock of which 170,900 have already been exercised. The shares of Common Stock were granted on December 29, 1994 and vest in five equal annual installments beginning one year from the date of issue.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Michael Pyle</signatureName>
        <signatureDate>2003-07-03</signatureDate>
    </ownerSignature>

</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
