If you discover an error on a previously filed tax return, how do you correct it?

Form 1040-X is the official mechanism for correcting a previously filed federal tax return. You can file an amended return to claim a refund within three years of the original filing deadline or two years from the date the tax was paid, whichever is later. Amended returns must be mailed — though the IRS has expanded electronic filing for 1040-X in recent years. The IRS does automatically correct simple math errors and will contact you if obvious forms are missing, but actual changes to income, credits, deductions, or filing status require a formal amended return. You can track the status of your amended return at the IRS website using the Where's My Amended Return tool.