It doesn’t happen all that often, but taxpayers sometimes receive corrected or missing tax information after they’ve already filed their federal income-tax returns. If it happens to you, don’t panic. The IRS has a process for amending returns.
You can correct mistakes on your federal income-tax return (Form 1040) by filing Form 1040X. It includes columns for listing amounts from your original return and the correct amounts and asks for an explanation of the specific changes being made. Any supporting documents and new or changed forms and schedules must be attached.
To receive a credit or refund, you generally must file Form 1040X within three years after the date you filed the original return or within two years after the date you paid the tax, whichever is later. If you owe additional tax, you’ll typically also have to pay interest on the balance due.