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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2018-02-23</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000072903</issuerCik>
        <issuerName>XCEL ENERGY INC</issuerName>
        <issuerTradingSymbol>XEL</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001629899</rptOwnerCik>
            <rptOwnerName>Clark Christopher B</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>414 NICOLLET MALL</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>MINNEAPOLIS</rptOwnerCity>
            <rptOwnerState>MN</rptOwnerState>
            <rptOwnerZipCode>55401</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President, NSPM</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Phantom Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0</value>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2018-02-23</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3578.753</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>44.77</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>3578.753</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>11763.760</value>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Each share of phantom stock represents the right to receive the cash value of one share of common stock.</footnote>
        <footnote id="F2">Shares of phantom stock become payable in accordance with the reporting person's distribution elections made pursuant to the Xcel Energy Deferred Compensation Plan (the &quot;Plan&quot;).  Subject to certain timing restrictions and other limitations based on the source of the amount deferred, the reporting person may generally transfer some or all of the balance in the Plan's Company stock account into an alternative Plan investment account.</footnote>
        <footnote id="F3">The number of shares of phantom stock reflects minor adjustments to the number of phantom shares credited to the reporting person's Company stock account due to the unitized nature of the Plan's Company stock fund.</footnote>
        <footnote id="F4">Amount reflects aggregate holdings as of February 26, 2018 and includes adjustments made by the Plan administrator to previously reported holdings, which were reported on a filing dated February 22, 2018.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Tara M. Stoffel, Attorney in Fact for Christopher B. Clark</signatureName>
        <signatureDate>2018-02-27</signatureDate>
    </ownerSignature>
</ownershipDocument>
