It depends on the type of mistake that you made:

• Many mathematical errors are caught in the processing of the tax return itself.
• If you did not attach a required schedule, the IRS will contact you and ask for the missing information.
• If you did not report all your income or did not claim a credit, you should file an amended or corrected return using Form 1040X (PDF), Amended U.S. Individual Income Tax Return.
When filing an amended or corrected return:
• Include copies of any schedules that have been changed or any Form W-2 (PDF) you did not include. File 1040 only after you have filed your original return. Generally, for a credit or refund, you must file Form 1040X within 3 years (including extensions) after the date you filed your original return or within 2 years after the date you paid the tax, whichever is later.
•  Please allow the IRS 8-12 weeks to process an amended return.

 

Many mistakes are corrected in processing and a letter of explanation is mailed at the time the refund is issued.

If the mistake was not corrected in processing, you need to:

No, an amended return must be filed on a paper Form 1040X (PDF), Amended U.S. Individual Income Tax Return, and mailed to the IRS at the address specified in the instructions to Form 1040X.   You may submit the form after the IRS processes your original return.

 

Allow the IRS 8-12 weeks to process the Amended Return

You will need to contact our assistance line toll-free at 800-829-1040 to receive information on the processing of your amended return. Amended/corrected returns are processed as quickly as possible. However, it could take 8 to 12 weeks to process an amended return.