<SUBMISSION>
<ACCESSION-NUMBER>0001140361-15-031710
<TYPE>3
<PUBLIC-DOCUMENT-COUNT>2
<PERIOD>20150812
<FILING-DATE>20150813
<DATE-OF-FILING-DATE-CHANGE>20150813
<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>717 TEXAS AVENUE
<STREET2>SUITE 1000
<CITY>HOUSTON
<STATE>TX
<ZIP>77002
<PHONE>7138302000
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>717 TEXAS AVENUE
<STREET2>SUITE 1000
<CITY>HOUSTON
<STATE>TX
<ZIP>77002
</MAIL-ADDRESS>
</ISSUER>
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>WEBB EDWARD THOMAS
<CIK>0001650702
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>3
<ACT>34
<FILE-NUMBER>001-12079
<FILM-NUMBER>151051293
</FILING-VALUES>
<MAIL-ADDRESS>
<STREET1>717 TEXAS AVENUE, SUITE 1000
<CITY>HOUSTON
<STATE>TX
<ZIP>77002
</MAIL-ADDRESS>
</REPORTING-OWNER>
<DOCUMENT>
<TYPE>3
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 3
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2015-08-12</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001650702</rptOwnerCik>
            <rptOwnerName>WEBB EDWARD THOMAS</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>717 TEXAS AVENUE, SUITE 1000</rptOwnerStreet1>
            <rptOwnerStreet2></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>Interim EVP, Power Operations</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>No securities are beneficially owned</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes></footnotes>

    <remarks>Exhibit 24.1 Power of Attorney</remarks>

    <ownerSignature>
        <signatureName>/s/ W. Thaddeus Miller by Power of Attorney</signatureName>
        <signatureDate>2015-08-13</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
<DOCUMENT>
<TYPE>EX-24.1
<SEQUENCE>2
<FILENAME>poaforedwardthomaswebb.txt
<DESCRIPTION>EXHIBIT 24.1 POWER OF ATTORNEY
<TEXT>
                                POWER OF ATTORNEY

         KNOW ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes
and appoints W. Thaddeus Miller and Jeff Koshkin, and each of them, his true
and lawful attorney-in-fact to:

         (1) execute for and on behalf of the undersigned, in the undersigned's
capacity as an officer of Calpine Corporation (the "Company"), any and all
Forms 3, 4 and 5 required to be filed by the undersigned in accordance with
Section 16(a) of the Securities Exchange Act of 1934, as amended (the "1934
Act"), and the rules thereunder;

         (2) 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

         (3) take and other action of any type whatsoever in connection with the
foregoing which, in the opinion of either 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 either such attorney-in-fact on
behalf of the undersigned, pursuant to this attorney-in-fact may approve in
his discretion.

         The undersigned hereby grants to such attorney-in-fact, and any one of
them, 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 and
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 her 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. 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's responsibilities to
comply with Section 16 of the 1934 Act.

         This Power of Attorney shall remain in full force and effect until the
undersigned is no longer required to file Forms 3, 4 and 5 with respect to the
undersigned'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 attorneys-in-fact.

         IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney
to be executed as of this 10th day of August 2015.


                                        /s/ Edward Thomas Webb
                                        ----------------------
                                        Edward Thomas Webb
</TEXT>
</DOCUMENT>
</SUBMISSION>
