I have previous W-2 forms can I still file them

[SteamTrain]

If you mean "previous" as in other years...not for 2018...

1) Yes....IF you did not file any tax returns for a prior year (meaning 2017 or earlier), and you have one or more  W-2 forms for that year, you can prepare them and "mail" them in (no e-filing allowed for any year but 2018 right now..and that ends in mid-October).  For the prior year's forms, you have to buy , download and install each year involved separately on a full MAC or Windows computer.  Only software back to 2015 is available,  (Window 7 or higher works for all years...if for a MAC...depends on what version you are using)

https://turbotax.intuit.com/personal-taxes/past-years-products/

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2) Yes...If you already  filed taxes for any of those prior years, and did not include the W-2 forms in question, then you have to amend the appropriate year's forms and mail in the amendment forms.

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3) NO...you cannot include a 2017..or earlier year W-2 in your 2018 tax returns

[Rainman12]

W-2s must be part of a return for Only the year they are for - either an original, or an amended return for the same year printed on the W-2. You can Not use a 2017 (or earlier) W-2 on your 2018 return. If you already filed your 2018 return, and want to add a 2018 W-2, then you have to amend 2018 (complete, print, and mail in  a Form 1040X with added W-2).