Make sure it's a 401k and not a ROTH 401k. (Make sure you are not in some state's Auto IRA program either...those may not be on a W-2 at all..or maybe in box 14 as "Information Only")
Is the contribution amount shown in box 12? IF so, what is the box 12 code?
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IF not an Auto-RA program and If not a ROTH 401k, then yeah, you'll need a corrected W-2.....wich could take a few weeks.
Chioces
1) go ahead and file as-is. You'll have a tax calculation than is higher than it really is supposed to be, and perhaps be required to pay extra with the filing............ but, after the first filing has been processed, by IRS and State you would then "Amend" in a couple months, to enter the W-2C and get some refund for the extra you paid.
or
2) File a Federal and State extension....pay any extra owed with the extension forms (if they do show a balance due), even if not quite right.....then file the final tax forms before mid-October.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
