<SUBMISSION>
<ACCESSION-NUMBER>0001140361-08-028288
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>2
<PERIOD>20081217
<FILING-DATE>20081218
<DATE-OF-FILING-DATE-CHANGE>20081218
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>CALPINE CORP
<CIK>0000916457
<ASSIGNED-SIC>4911
<IRS-NUMBER>770212977
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>50 WEST SAN FERNANDO ST
<CITY>SAN JOSE
<STATE>CA
<ZIP>95113
<PHONE>4089955115
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>50 W SAN FERNANDO
<STREET2>SUITE 500
<CITY>SAN JOSE
<STATE>CA
<ZIP>95113
</MAIL-ADDRESS>
</ISSUER>
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>RAUF ZAMIR
<CIK>0001437010
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>001-12079
<FILM-NUMBER>081258462
</FILING-VALUES>
<BUSINESS-ADDRESS>
<PHONE>713-830-2000
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>717 TEXAS AVENUE, SUITE 1000
<CITY>HOUSTON
<STATE>TX
<ZIP>77002
</MAIL-ADDRESS>
</REPORTING-OWNER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-12-17</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000916457</issuerCik>
        <issuerName>CALPINE CORP</issuerName>
        <issuerTradingSymbol>CPN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001437010</rptOwnerCik>
            <rptOwnerName>RAUF ZAMIR</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>CALPINE CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>717 TEXAS AVENUE, SUITE 1000</rptOwnerStreet2>
            <rptOwnerCity>HOUSTON</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>77002</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP, Chief Financial Officer</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Non-Qualified Stock Option (Right to Buy)</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>8.01</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2008-12-17</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>100000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2009-12-17</value>
            </exerciseDate>
            <expirationDate>
                <value>2018-12-17</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>100000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>144900</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Option granted on December 17, 2008, pursuant to the Company's 2008 Equity Incentive Plan. The option becomes exercisable over a three-year period: 33-1/3% on December 17, 2009, 33-1/3% on December 17, 2010, and 33-1/3% on December 17, 2011.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/  W. Thaddeus Miller by Power of Attorney</signatureName>
        <signatureDate>2008-12-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
<DOCUMENT>
<TYPE>EX-24
<SEQUENCE>2
<FILENAME>poa1.htm
<DESCRIPTION>POWER OF ATTORNEY
<TEXT>
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    <title>Unassociated Document</title>
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    <div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 0pt; MARGIN-RIGHT: 0pt" align="center"><font style="DISPLAY: inline; FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: Times New Roman"><font style="DISPLAY: inline; TEXT-DECORATION: underline">POWER OF
ATTORNEY</font></font></div>
    <div style="DISPLAY: block; TEXT-INDENT: 0pt"><br></div>
    <div style="DISPLAY: block; TEXT-INDENT: 0pt"><br></div>
    <div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 36pt; MARGIN-RIGHT: 0pt" align="left"><font style="DISPLAY: inline; FONT-SIZE: 10pt; FONT-FAMILY: Times New Roman"><font style="DISPLAY: inline; FONT-WEIGHT: bold">KNOW ALL MEN BY THESE
PRESENTS</font>, that the undersigned hereby constitutes and appoints <font style="DISPLAY: inline; FONT-WEIGHT: bold">W. Thaddeus Miller</font> his true
and lawful attorney-in-fact to:</font></div>
    <div style="DISPLAY: block; TEXT-INDENT: 0pt"><br></div>
    <div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 36pt; MARGIN-RIGHT: 0pt" align="left"><font style="DISPLAY: inline; FONT-SIZE: 10pt; FONT-FAMILY: Times New Roman">(1)&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;execute
for and on behalf of the undersigned, in the undersigned&#8217;s capacity as an
officer and/or director of Calpine Corporation (the &#8220;Company&#8221;), any and all
Forms 3, 4 or 5 required to be filed by the undersigned in accordance with
Section 16(a) of the Securities Exchange Act of 1934, as amended (the &#8220;1934
Act&#8221;), and the rules thereunder;</font></div>
    <div style="DISPLAY: block; TEXT-INDENT: 0pt"><br></div>
    <div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 36pt; MARGIN-RIGHT: 0pt" align="left"><font style="DISPLAY: inline; FONT-SIZE: 10pt; FONT-FAMILY: Times New Roman">(2)&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;do
and perform any and all acts for and on behalf of the undersigned which may be
necessary or desirable to complete and execute any such Forms 3, 4 or 5 and
timely file each form with the United States Securities and Exchange Commission
and any stock exchange or similar authority; and</font></div>
    <div style="DISPLAY: block; TEXT-INDENT: 0pt"><br></div>
    <div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 36pt; MARGIN-RIGHT: 0pt" align="left"><font style="DISPLAY: inline; FONT-SIZE: 10pt; FONT-FAMILY: Times New Roman">(3)&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;take
any other action of any type whatsoever in connection with the foregoing which,
in the opinion of such attorney-in-fact, may be of benefit to, in the best
interest of, or legally required by, the undersigned, it being understood that
the documents executed by such attorney-in-fact on behalf of the undersigned,
pursuant to this attorney-in-fact may approve in his discretion.</font></div>
    <div style="DISPLAY: block; TEXT-INDENT: 0pt"><br></div>
    <div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 36pt; MARGIN-RIGHT: 0pt" align="left"><font style="DISPLAY: inline; FONT-SIZE: 10pt; FONT-FAMILY: Times New Roman">The
undersigned hereby grants to such attorney-in-fact full power and authority to
do and perform all and every act and thing whatsoever requisite, necessary, and
proper to be done in the exercise of any of the rights and powers herein
granted, as fully to all intents and purposes as the undersigned might or could
do if personally present, with full power of substitution or revocation, hereby
ratifying and confirming all that such attorney-in-fact, or his substitute or
substitutes, shall lawfully do or cause to be done by virtue of the Power of
Attorney and the rights and powers herein granted.&#160;&#160;The undersigned
acknowledges that none of such attorneys-in-fact, in serving in such capacity at
the request of the undersigned, is hereby assuming, nor is the Company hereby
assuming, any of the undersigned&#8217;s responsibilities to comply with
Section&#160;16 of the 1934 Act.</font></div>
    <div style="DISPLAY: block; TEXT-INDENT: 0pt"><br></div>
    <div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 36pt; MARGIN-RIGHT: 0pt" align="left"><font style="DISPLAY: inline; FONT-SIZE: 10pt; FONT-FAMILY: Times New Roman">This
Power of Attorney shall remain in full force and effect until the undersigned is
no longer required to file Forms 3, 4 or 5 with respect to the undersigned&#8217;s
holdings of and transactions in securities issued by the Company, unless earlier
revoked by the undersigned in a signed writing delivered to the foregoing
attorney-in-fact.</font></div>
    <div style="DISPLAY: block; TEXT-INDENT: 0pt"><br></div>
    <div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 36pt; MARGIN-RIGHT: 0pt" align="left"><font style="DISPLAY: inline; FONT-SIZE: 10pt; FONT-FAMILY: Times New Roman"><font style="DISPLAY: inline; FONT-WEIGHT: bold">IN WITNESS WHEREOF</font>, the
undersigned has caused this Power of Attorney to be executed as of this 18th day
of December 2008.</font></div>
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    <div>
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      Rauf</font></div>
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</SUBMISSION>
