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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-06-08</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000749251</issuerCik>
        <issuerName>GARTNER INC</issuerName>
        <issuerTradingSymbol>IT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001159187</rptOwnerCik>
            <rptOwnerName>UBBEN JEFFREY W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>435 PACIFIC AVENUE, FOURTH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SAN FRANCISCO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94133</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001129787</rptOwnerCik>
            <rptOwnerName>VA PARTNERS LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>435 PACIFIC AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>FOURTH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>SAN FRANCISCO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94133</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001351069</rptOwnerCik>
            <rptOwnerName>ValueAct Capital Management, L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>435 PACIFIC AVENUE, 4TH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SAN FRANCISCO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94133</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001351073</rptOwnerCik>
            <rptOwnerName>ValueAct Capital Management, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>435 PACIFIC AVENUE, 4TH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SAN FRANCISCO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94133</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Restricted Stock Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0.0005</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2006-06-08</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4791</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2007-06-08</value>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2007-06-08</value>
                <footnoteId id="F1"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4791</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4791</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F3"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">One Hundred Percent (100%) of the Restricted Stock Units shall vest on the one (1) year anniversary of the Vesting Commencement Date, 06/08/2006, subject to Grantee's Continued Service through such date.</footnote>
        <footnote id="F2">Column 8 is not a required reportable field.</footnote>
        <footnote id="F3">Under an agreement with ValueAct Capital, Jeffrey W. Ubben is deemed to hold the restricted stock units for the benefit of ValueAct Capital Master Fund, L.P. and indirectly for (i) VA Partners, L.L.C. as General Partner of ValueAct Capital Master Fund, L.P., (ii) ValueAct Capital Management, L.P. as the manager of ValueAct Capital Master Fund, L.P. and (iii) ValueAct Capital Management, LLC as General Partner of ValueAct Capital Management, L.P.  Jeffrey W. Ubben is a director of Gartner, Inc. and Managing Member of VA Partners, LLC and ValueAct Capital Management, LLC.  Peter H. Kamin and George F. Hamel, Jr. are Managing Members of VA Partners, LLC and ValueAct Capital Management, LLC. The reporting persons disclaim beneficial ownership of the reported stock except to the extent of their pecuniary interest therein.</footnote>
    </footnotes>

    <remarks>Joint Filer Information:

Name: ValueAct Capital Master Fund, L.P.,
Address: 435 Pacific Avenue, Fourth Floor, San Francisco, CA 94133
Designated Filer: Jeffrey W. Ubben
Issuer and Ticker Symbol: Gartner, Inc. (IT)
Date of Event Requiring Statement: June 8, 2006

Name: VA Partners, LLC
Address: 435 Pacific Avenue, Fourth Floor, San Francisco, CA 94133
Designated Filer: Jeffrey W. Ubben
Issuer and Ticker Symbol: Gartner, Inc. (IT)
Date of Event Requiring Statement: June 8, 2006

Name: ValueAct Capital Management, L.P.
Address: 435 Pacific Avenue, Fourth Floor, San Francisco, CA 94133
Designated Filer: Jeffrey W. Ubben
Issuer and Ticker Symbol: Gartner, Inc. (IT)
Date of Event Requiring Statement: June 8, 2006

Name: ValueAct Capital Management, LLC
Address: 435 Pacific Avenue, Fourth Floor, San Francisco, CA 94133
Designated Filer: Jeffrey W. Ubben
Issuer and Ticker Symbol: Gartner, Inc. (IT)
Date of Event Requiring Statement: June 8, 2006

Name: George F. Hamel, Jr.
Address: 435 Pacific Avenue, Fourth Floor, San Francisco, CA 94133
Designated Filer: Jeffrey W. Ubben
Issuer and Ticker Symbol: Gartner, Inc. (IT)
Date of Event Requiring Statement: June 8, 2006

Name: Peter H. Kamin
Address: 435 Pacific Avenue, Fourth Floor, San Francisco, CA 94133
Designated Filer: Jeffrey W. Ubben
Issuer and Ticker Symbol: Gartner, Inc. (IT)
Date of Event Requiring Statement: June 8, 2006</remarks>

    <ownerSignature>
        <signatureName>/s/ Jeffrey W. Ubben</signatureName>
        <signatureDate>2006-06-12</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>VA PARTNERS, L.L.C., By:/s/ George F. Hamel. Jr., Managing Member</signatureName>
        <signatureDate>2006-06-12</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>VALUEACT CAPITAL MASTER FUND, L.P., By:  VA PARTNERS, L.L.C., its General Partner, By:/s/ George F. Hamel. Jr., Managing Member</signatureName>
        <signatureDate>2006-06-12</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>VALUEACT CAPITAL  MANAGEMENT, L.P., By:  VALUEACT CAPITAL MANAGEMENT, LLC, its General Partner, By:/s/ George F. Hamel. Jr., Managing Member</signatureName>
        <signatureDate>2006-06-12</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>VALUEACT CAPITAL MANAGEMENT, LLC, By:/s/ George F. Hamel. Jr., Managing Member</signatureName>
        <signatureDate>2006-06-12</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ George F. Hamel, Jr.</signatureName>
        <signatureDate>2006-06-12</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Peter H. Kamin</signatureName>
        <signatureDate>2006-06-12</signatureDate>
    </ownerSignature>
</ownershipDocument>
