<SEC-DOCUMENT>0001998332-25-000005.txt : 20250910
<SEC-HEADER>0001998332-25-000005.hdr.sgml : 20250910
<ACCEPTANCE-DATETIME>20250910135037
ACCESSION NUMBER:		0001998332-25-000005
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20250606
FILED AS OF DATE:		20250910
DATE AS OF CHANGE:		20250910

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Bridge T. Craig
		CENTRAL INDEX KEY:			0001998332
		ORGANIZATION NAME:           	

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-42125
		FILM NUMBER:		251305440

	MAIL ADDRESS:	
		STREET 1:		1550 DIGITAL DRIVE, #300
		CITY:			LEHI
		STATE:			UT
		ZIP:			84043

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Waystar Holding Corp.
		CENTRAL INDEX KEY:			0001990354
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-COMPUTER INTEGRATED SYSTEMS DESIGN [7373]
		ORGANIZATION NAME:           	06 Technology
		EIN:				000000000
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		1550 DIGITAL DRIVE, #300
		CITY:			LEHI
		STATE:			UT
		ZIP:			84043
		BUSINESS PHONE:		844-492-9782

	MAIL ADDRESS:	
		STREET 1:		1550 DIGITAL DRIVE, #300
		CITY:			LEHI
		STATE:			UT
		ZIP:			84043
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wk-form4_1757526634.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2025-06-06</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001990354</issuerCik>
        <issuerName>Waystar Holding Corp.</issuerName>
        <issuerTradingSymbol>WAY</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001998332</rptOwnerCik>
            <rptOwnerName>Bridge T. Craig</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1550 DIGITAL DRIVE, #300</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>LEHI</rptOwnerCity>
            <rptOwnerState>UT</rptOwnerState>
            <rptOwnerZipCode>84043</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Transformation Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>1</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2025-06-06</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>14488</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>40.55</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>668355</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2025-09-08</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>85000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>40.0618</value>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>583355</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Includes unvested RSUs.</footnote>
        <footnote id="F2">This transaction was not timely filed. The transaction represents shares of common stock withheld to pay taxes upon vesting of Non-Qualified Stock Options granted to the Reporting Person on June 6, 2024. The number of shares withheld was determined on June 6, 2025, based on the closing price of WAY common stock on that date. In addition, the total number of shares beneficially owned following the reported transaction reflects a correction to prior filings to account for an earlier misclassification of an option exercise. The ending balance reported herein is accurate and reflects the Reporting Person's current holdings.</footnote>
        <footnote id="F3">The price reported in Column 4 is a weighted average price. These shares of common stock, par value $0.01 per share (&quot;Common Stock&quot;) of Waystar Holding Corp. (the &quot;Issuer&quot;) were sold in multiple transactions ranging from $40.00 to $40.22, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares of Common Stock sold at each separate price in the range set forth in this footnote.</footnote>
        <footnote id="F4">These transactions occurred automatically pursuant to a plan adopted by the Reporting Person on November 27, 2024 that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c).</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Gregory R. Packer, as Attorney-in-Fact</signatureName>
        <signatureDate>2025-09-10</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
