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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-10-25</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0000876437</issuerCik>
        <issuerName>MGIC INVESTMENT CORP</issuerName>
        <issuerTradingSymbol>MTG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001041956</rptOwnerCik>
            <rptOwnerName>BUSH MARY K</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O BUSH INTERNATIONAL, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>3509 WOODBINE STREET</rptOwnerStreet2>
            <rptOwnerCity>CHEVY CHASE</rptOwnerCity>
            <rptOwnerState>MD</rptOwnerState>
            <rptOwnerZipCode>20815</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <footnotes></footnotes>

    <remarks>The reporting person ceased to be a Director of the Issuer, as of October 25, 2006.  This Form 4 has been signed by the reporting person's attorney-in-fact pursuant to a previously filed power of attorney.</remarks>

    <ownerSignature>
        <signatureName>Dan D. Stilwell, Attorney-in-fact</signatureName>
        <signatureDate>2006-10-25</signatureDate>
    </ownerSignature>
</ownershipDocument>
