How to Amend a Tax Return You Already Filed

Learn when and how to file Form 1040X to correct mistakes on your tax return and get the refund you're owed.

1. Check if you actually need to amend. The IRS automatically corrects basic math errors and some missing forms like W-2s or 1099s. You only need Form 1040X for changes to income, deductions, credits, or filing status that affect your tax liability. Wait to see if the IRS fixes simple mistakes first.
2. Gather your original return and new documents. Pull your filed tax return and any new tax documents you missed. Common reasons for amendments include forgotten 1099s, missed deductions, incorrect filing status, or claiming dependents you forgot. Have both your original numbers and corrected numbers ready.
3. Download and complete Form 1040X. Form 1040X has three columns: original amounts, changes, and corrected amounts. Fill out the difference between what you originally reported and what you should have reported. The form walks you through each line item from your 1040.
4. Explain your changes clearly. Use Part III of Form 1040X to explain what you're changing and why. Be specific but brief. Attach any new forms or schedules that support your changes, like a Schedule A for itemized deductions you forgot to claim.
5. Mail the amendment to the correct IRS center. Form 1040X must be mailed — you cannot e-file amendments for most tax years. The form instructions list which processing center to use based on your state. Send it certified mail to confirm delivery.
6. Track your amendment and wait for processing. Check your amendment status on IRS.gov using the 'Where's My Amended Return?' tool after 3 weeks. Processing typically takes 8-12 weeks for refunds, longer during busy seasons. The IRS will mail you a notice explaining any changes they made to your amendment.