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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-01-19</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001042017</issuerCik>
        <issuerName>FRMO CORP</issuerName>
        <issuerTradingSymbol>FRMO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001260568</rptOwnerCik>
            <rptOwnerName>GOLDSTEIN LAWRENCE J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>7865 PALMER AVE 108</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>LARCHMONT</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10538</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2007-01-19</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>13900</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>8.22</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2620169</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <remarks>Ownership Breakdown: Lawrence J. Goldstein beneficially owns directly 1,935,256 shares in his name and 2,500 shares in the name of Lawrence J. Goldstein, IRA. As President of Santa Monica Partners Asset Management, LLC, which is General Partner of Santa Monica Partners, L.P., and of Santa Monica Partners II, L.P., which beneficially owns indirectly 663,513 shares and 5,000 shares, respectively.

The transaction dated 1/19/07 reported on this From 4 resulted from an unauthorized purchase of 13,900 shares (the &quot;Unauthorized Shares&quot;) for the account of Santa Monica Partners, LP. (&quot;SMPLP&quot;)  Upon discovery of the purchase of the Unauthorized Shares, such shares were transferred from SMPLP to the &quot;error account&quot; of L.J. Goldstein &amp; Company, Incorporated, an affiliate of Goldstein.

Goldstein is disputing the purchase of, and any obligation to pay for, the Unauthorized Shares, pending the completion of an investigation.  However, in order to assure that the Partnership is not the victim of the purchase of the Unauthorized Shares, Goldstein authorized the transfer of such shares to his personal account at Pershing, LLC.  Such transaction was effected on 1/19/07</remarks>

    <ownerSignature>
        <signatureName>Lawrence J. Goldstein</signatureName>
        <signatureDate>2007-01-19</signatureDate>
    </ownerSignature>
</ownershipDocument>
