In the haste to get taxes prepared and filed quickly, it's easy to forget a W-2 form when you send your return to the Internal Revenue Service. If you simply forgot to include a copy of it with your return, you can usually wait for the IRS to contact you. However, if you forgot to use its information when calculating your return, you'll have to file an amended return.
Reported, But Not Filed
You don't have to file an amended tax return for forgetting a W-2, as long as you included its information to figure out your tax burden. The IRS will send you a request for the missing document, and you'll provide it to the address specified. If you expect a refund, you may get it later than usual, as the agency may wait to receive the W-2 before issuing the check.
If you forgot about the W-2 entirely and didn't include it when figuring out your income, you'll have to file an amended return. Fill out a 1040X including that information, and mail the completed form – and a check for any additional tax owed – to the IRS as soon as possible. If you were due a refund from the first tax return you filed, wait to send the 1040X until you receive that refund. Regardless of how you filed your original return, a 1040X has to be filled out on paper. The IRS should already have a copy of the W-2 from your employer and matches it to the information you provide, so failing to include that information creates a discrepancy that increases your audit risk.