When should I file an amended tax return, and when should I leave it alone?

File an amended return (Form 1040-X) when you discover a real error that changes your tax: missed income, a forgotten deduction or credit, the wrong filing status, or a corrected 1099 or K-1 that arrived after you filed. You don't need to amend for simple math errors — the IRS corrects those automatically — or when you'll receive an IRS notice proposing the same change anyway. Amend to claim a refund within three years of the original filing date (or two years from when you paid, if later), after which the money is generally lost. If the change increases your tax, amend and pay promptly to limit interest. Weigh the effort: a tiny change may not be worth filing. You can now e-file 1040-X for recent years through most software.