<SEC-DOCUMENT>0001562180-21-006640.txt : 20211025
<SEC-HEADER>0001562180-21-006640.hdr.sgml : 20211025
<ACCEPTANCE-DATETIME>20211025192109
ACCESSION NUMBER:		0001562180-21-006640
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20211021
FILED AS OF DATE:		20211025
DATE AS OF CHANGE:		20211025

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Sahasi Jayesh
		CENTRAL INDEX KEY:			0001841662

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-39965
		FILM NUMBER:		211345367

	MAIL ADDRESS:	
		STREET 1:		934 LUNDY LN
		CITY:			LOS ALTOS
		STATE:			CA
		ZIP:			94024

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			ON24 INC.
		CENTRAL INDEX KEY:			0001110611
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-PREPACKAGED SOFTWARE [7372]
		IRS NUMBER:				000000000
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		50 BEALE STREET, 8TH FLOOR
		CITY:			SAN FRANCISCO
		STATE:			CA
		ZIP:			94105
		BUSINESS PHONE:		(415) 369-8000

	MAIL ADDRESS:	
		STREET 1:		50 BEALE STREET, 8TH FLOOR
		CITY:			SAN FRANCISCO
		STATE:			CA
		ZIP:			94105

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	ON24 INC
		DATE OF NAME CHANGE:	20000329
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primarydocument.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2021-10-21</periodOfReport>

    <notSubjectToSection16>false</notSubjectToSection16>

    <issuer>
        <issuerCik>0001110611</issuerCik>
        <issuerName>ON24 INC.</issuerName>
        <issuerTradingSymbol>ONTF</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001841662</rptOwnerCik>
            <rptOwnerName>Sahasi Jayesh</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O ON24, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>50 BEALE STREET, 8TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>SAN FRANCISCO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94015</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>false</isDirector>
            <isOfficer>true</isOfficer>
            <isTenPercentOwner>false</isTenPercentOwner>
            <isOther>false</isOther>
            <officerTitle>EV President, Product and CTO</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2021-10-21</value>
            </transactionDate>
            <deemedExecutionDate>
                <value>2021-10-21</value>
            </deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>false</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>70000.00</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>20.543</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>350210.00</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2021-10-22</value>
            </transactionDate>
            <deemedExecutionDate>
                <value>2021-10-22</value>
            </deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>false</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>37614.00</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>20.1531</value>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>312596.00</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2021-10-25</value>
            </transactionDate>
            <deemedExecutionDate>
                <value>2021-10-25</value>
            </deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>false</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>32386.00</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>20.2444</value>
                    <footnoteId id="F4"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>280210.00</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">The transactions reported in this Form 4 were effected pursuant to a Rule 10B5-1 trading plan adopted by the reporting person on May 28, 2021.</footnote>
        <footnote id="F2">The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $20.11 to $20.70, inclusive. The reporting person undertakes to provide to Issuer, any security holder of Issuer, or the staff of the Security and Exchange Commission, upon request, full information regarding the number of shares sold in each separate price within the ranges set forth in footnote (2) to this Form 4.</footnote>
        <footnote id="F3">The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $20.00 to $20.49, inclusive. The reporting person undertakes to provide to Issuer, any security holder of Issuer, or the staff of the Security and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in footnote (3) to this Form 4.</footnote>
        <footnote id="F4">The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions ranging from $20.03 to $20.51, inclusive. The reporting person undertakes to provide to Issuer, any security holder of Issuer, or the staff of the Security and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in footnote (3) to this Form 4.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Jayesh Sahasi, William Weesner, Attorney-in-Fact</signatureName>
        <signatureDate>2021-10-25</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
