How long do I have to amend a return to claim a missed refund?

Generally you must file Form 1040-X within three years of the date you filed the original return, or within two years of the date you actually paid the tax, whichever is later. A return filed before the April deadline is treated as filed on the deadline for this clock. Miss the window and the IRS keeps the refund permanently, even if you clearly overpaid — this trips up people who forgot a deduction or an education credit years ago. Special longer periods apply for a few situations, such as bad debts, worthless securities (seven years), and net operating loss or foreign-tax-credit carrybacks. If you're close to the deadline, file the 1040-X even if imperfect to preserve the claim. Confirm current rules on irs.gov, since procedures for e-filing amended returns keep expanding.