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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-07-01</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001418814</rptOwnerCik>
            <rptOwnerName>ValueAct Holdings, 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>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>See remarks</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001464912</rptOwnerCik>
            <rptOwnerName>ValueAct Capital Master Fund, L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>435 PACIFIC AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>4TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>SAN FRANCISCO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94133</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>See remarks</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001418812</rptOwnerCik>
            <rptOwnerName>VA Partners I, 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>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>See remarks</otherText>
        </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>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>See remarks</otherText>
        </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>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>See remarks</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001418813</rptOwnerCik>
            <rptOwnerName>ValueAct Holdings GP, 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>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>See remarks</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock, par value $.01 per share</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5080013</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Common Stock Equivalents (CSE)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2011-07-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>169</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>169</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>16096</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote</value>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The reported stock is owned directly by ValueAct Capital Master Fund, L.P. and may be deemed to be beneficially owned by (i) VA Partners I, LLC as General Partner of ValueAct Capital Master Fund, L.P., (ii) ValueAct Capital Management, L.P. as the manager of of ValueAct Capital Master Fund, L.P., (iii) ValueAct Capital Management, LLC as General Partner of ValueAct Capital Management, L.P., (iv) ValueAct Holdings, L.P. as the sole owner of the limited partnership interests of ValueAct Capital Management, L.P. and the membership interests of ValueAct Capital Management, LLC and as the majority owner of the membership interests of VA Partners I, LLC and (v) ValueAct Holdings GP, LLC as General Partner of ValueAct Holdings, L.P.</footnote>
        <footnote id="F2">These are Common Stock Equivalents received as compensation for Jeffrey W. Ubben's service as an outside director of Gartner, Inc.  They were granted under the Company's 2003 Long-Term Incentive Plan (LTIP).  The Common Stock Equivalents convert into Gartner Common Stock on the date the outside director's continuous status as a director terminates, or as otherwise provided in the 2003 LTIP.</footnote>
        <footnote id="F3">Under an agreement with ValueAct Capital, Jeffrey W. Ubben is deemed to hold the Common Stock Equivalents for the benefit of ValueAct Capital Master Fund, L.P. &amp; indirectly for (i) VA Partners I, LLC 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., (iii) ValueAct Capital Management, LLC as General Partner of ValueAct Capital Management, L.P., (iv) ValueAct Holdings, L.P. as the sole owner of the limited partnership interests of ValueAct Capital Management, L.P. and the membership interests of ValueAct Capital Management, LLC and as the majority owner of the membership interests of VA Partners I, LLC and (v) ValueAct Holdings GP, LLC as General Partner of ValueAct Holdings, L.P.</footnote>
        <footnote id="F4">Each reporting person listed herein disclaims beneficial ownership of the reported securities except to the extent of its pecuniary interest therein, and this report shall not be deemed an admission that such person is the beneficial owner of the securities for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, or for any other purpose.</footnote>
    </footnotes>

    <remarks>-The reporting persons herein may be deemed to be members of a &quot;group&quot; for purposes of the Securities Exchange Act of 1934, as amended. Each reporting person disclaims beneficial ownership of any securities deemed to be owned by the group that are not directly owned by such reporting person. This report shall not be deemed an admission that such reporting person is a member of a group or the beneficial owner of any securities not directly owned by such reporting person.

-Jeffrey W. Ubben, a member of the management board of ValueAct Holdings GP, LLC, serves on the board of directors of the Issuer.  As a result, the reporting persons herein may be deemed directors by deputization.

Joint Filer Information:

Name: ValueAct Capital Master Fund, L.P.
Address: 435 Pacific Avenue, 4th Floor, San Francisco, CA 94133
Designated Filer: ValueAct Holdings, L.P.
Issuer and Ticker: Gartner, Inc. (IT)
Date of Event Requiring Statement: 07/01/2011

Name: VA Partners I, LLC
Address: 435 Pacific Avenue, 4th Floor, San Francisco, CA 94133
Designated Filer: ValueAct Holdings, L.P.
Issuer and Ticker: Gartner, Inc. (IT)
Date of Event Requiring Statement: 07/01/2011

Name: ValueAct Capital Management, L.P.
Address: 435 Pacific Avenue, 4th Floor, San Francisco, CA 94133
Designated Filer: ValueAct Holdings, L.P.
Issuer and Ticker: Gartner, Inc. (IT)
Date of Event Requiring Statement: 07/01/2011

Name: ValueAct Capital Management, LLC
Address: 435 Pacific Avenue, 4th Floor, San Francisco, CA 94133
Designated Filer: ValueAct Holdings, L.P.
Issuer and Ticker: Gartner, Inc. (IT)
Date of Event Requiring Statement: 07/01/2011

Name: ValueAct Holdings GP, LLC
Address: 435 Pacific Avenue, 4th Floor, San Francisco, CA 94133
Designated Filer: ValueAct Holdings, L.P.
Issuer and Ticker: Gartner, Inc. (IT)
Date of Event Requiring Statement: 07/01/2011</remarks>

    <ownerSignature>
        <signatureName>VALUEACT HOLDINGS, L.P., By:  VALUEACT HOLDINGS GP, LLC, its General Partner, By:/s/ George F. Hamel. Jr., Chief Operating Officer</signatureName>
        <signatureDate>2011-07-06</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>VALUEACT CAPITAL MASTER FUND, L.P., By:  VA PARTNERS I, LLC, its General Partner, By:/s/ George F. Hamel. Jr., Chief Operating Officer</signatureName>
        <signatureDate>2011-07-06</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>VA PARTNERS I, LLC, By:/s/ George F. Hamel. Jr., Chief Operating Officer</signatureName>
        <signatureDate>2011-07-06</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>VALUEACT CAPITAL  MANAGEMENT, L.P., By:  VALUEACT CAPITAL MANAGEMENT, LLC, its General Partner, By:/s/ George F. Hamel. Jr., Chief Operating Officer</signatureName>
        <signatureDate>2011-07-06</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>VALUEACT CAPITAL MANAGEMENT, LLC, By:/s/ George F. Hamel. Jr., Chief Operating Officer</signatureName>
        <signatureDate>2011-07-06</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>VALUEACT HOLDINGS GP, LLC, By:/s/ George F. Hamel. Jr., Chief Operating Officer</signatureName>
        <signatureDate>2011-07-06</signatureDate>
    </ownerSignature>
</ownershipDocument>
