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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2020-06-05</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001121788</issuerCik>
        <issuerName>GARMIN LTD</issuerName>
        <issuerTradingSymbol>GRMN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001134084</rptOwnerCik>
            <rptOwnerName>BURRELL JONATHAN</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>18899 HAPPY HOLLOW ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SPRING HILL</rptOwnerCity>
            <rptOwnerState>KS</rptOwnerState>
            <rptOwnerZipCode>66083</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Registered Shares</value>
            </securityTitle>
            <transactionDate>
                <value>2020-06-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1594</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5975</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Registered Shares</value>
            </securityTitle>
            <transactionDate>
                <value>2020-06-07</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>501</value>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>96.53</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5474</value>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Registered Shares</value>
            </securityTitle>
            <transactionDate>
                <value>2020-06-08</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>216</value>
                    <footnoteId id="F5"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>99.3</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5258</value>
                    <footnoteId id="F6"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Registered Shares</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>30000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By trust</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Registered Shares</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>17350</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By trust</value>
                    <footnoteId id="F7"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Registered Shares</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>8413050</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By CLATs</value>
                    <footnoteId id="F8"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Registered Shares</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>14264720</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By GRATs</value>
                    <footnoteId id="F9"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Consists of restricted stock units (&quot;RSUs&quot;) awarded to the reporting person under the Garmin Ltd. Non-Employee Directors' Equity Incentive Plan, which RSUs vest on June 5, 2021 and can be settled only in Registered Shares.</footnote>
        <footnote id="F2">Consists of (a) 648 Registered Shares, and (b) unvested RSUs awarded to the reporting person under the Garmin Ltd. Non-Employee Directors' Equity Incentive Plan that can be settled only in Registered Shares, which RSUs consist of: (i) RSUs granted on June 5, 2020 that vest as to 1,594 shares on June 5, 2021; (ii) RSUs granted on June 7, 2019 that vest as to 2,004 shares on June 7, 2020; and (iii) RSUs granted on June 8, 2018 that vest as to 864 shares on June 8, 2020, and as to 865 shares on June 8, 2021.</footnote>
        <footnote id="F3">Consists of Registered Shares withheld to pay taxes resulting from the June 7, 2020 vesting and settlement of RSUs awarded to the reporting person with respect to 2,004 Registered Shares.</footnote>
        <footnote id="F4">Consists of (a) 2,151 Registered Shares, and (b) unvested RSUs awarded to the reporting person under the Garmin Ltd. Non-Employee Directors' Equity Incentive Plan that can be settled only in Registered Shares, which RSUs consist of: (i) RSUs granted on June 5, 2020 that vest as to 1,594 shares on June 5, 2021; and (ii) RSUs granted on June 8, 2018 that vest as to 864 shares on June 8, 2020, and as to 865 shares on June 8, 2021.</footnote>
        <footnote id="F5">Consists of Registered Shares withheld to pay taxes resulting from the June 8, 2020 vesting and settlement of RSUs awarded to the reporting person with respect to 864 Registered Shares.</footnote>
        <footnote id="F6">Consists of (a) 2,799 Registered Shares, and (b) unvested RSUs awarded to the reporting person under the Garmin Ltd. Non-Employee Directors' Equity Incentive Plan that can be settled only in Registered Shares, which RSUs consist of: (i) RSUs granted on June 5, 2020 that vest as to 1,594 shares on June 5, 2021; and (ii) RSUs granted on June 8, 2018 that vest as to 865 shares on June 8, 2021.</footnote>
        <footnote id="F7">The reporting person is a co-trustee of his mother's revocable trust and is his mother's attorney-in-fact, and also holds a remainder interest in the securities held in such trust.  The reporting person disclaims beneficial ownership of the reported securities except to the extent of his pecuniary interest therein.</footnote>
        <footnote id="F8">The reporting person is a co-trustee of several charitable lead annuity trusts (CLATs) and holds a remainder interest therein.  The reporting person disclaims beneficial ownership of the reported securities except to the extent of his pecuniary interest therein.</footnote>
        <footnote id="F9">The reporting person is a co-trustee of several grantor retained annuity trusts (GRATs) established by his mother, and he holds a remainder interest therein.  The reporting person disclaims beneficial ownership of the reported securities except to the extent of his pecuniary interest therein.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Jonathan Burrell</signatureName>
        <signatureDate>2020-06-09</signatureDate>
    </ownerSignature>
</ownershipDocument>
