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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2004-09-03</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000101390</issuerCik>
        <issuerName>UNITED MORTGAGE TRUST</issuerName>
        <issuerTradingSymbol>none</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000101390</rptOwnerCik>
            <rptOwnerName>UNITED MORTGAGE TRUST</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>5740 PROSPECT</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 1000</rptOwnerStreet2>
            <rptOwnerCity>DALLAS</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>75206</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Shares of Beneficial Interest</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>20</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2004-09-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>20</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2003-12-31</value>
            </exerciseDate>
            <expirationDate>
                <value>2008-12-31</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>United Mortgage Trust</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>2500</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>15000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Shares of Beneficial Interest</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>20</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2004-09-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>20</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>1998-12-31</value>
            </exerciseDate>
            <expirationDate>
                <value>2003-12-31</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>United Mortgage Trust</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>2500</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>12500</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <ownerSignature>
        <signatureName>Douglas R Evans</signatureName>
        <signatureDate>2004-09-08</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Richard D. O'Connor, Jr.</signatureName>
        <signatureDate>2004-09-08</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2004-09-03
0
0000101390
UNITED MORTGAGE TRUST
none
0000101390
UNITED MORTGAGE TRUST
5740 PROSPECT
SUITE 1000
DALLAS
TX
75206
1
0
0
0
Shares of Beneficial Interest
20
2004-09-03
4
A
0
2500
20
A
2003-12-31
2008-12-31
United Mortgage Trust
2500
15000
D
Shares of Beneficial Interest
20
2004-09-03
4
A
0
2500
20
D
1998-12-31
2003-12-31
United Mortgage Trust
2500
12500
D
Douglas R Evans
2004-09-08
Richard D. O'Connor, Jr.
2004-09-08