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 service will contact you and ask for the missing information.

If you did not report all your income or did not claim a credit, you are entitled to file an amended or corrected return using Form 1040X (PDF), Amended U.S. Individual Income Tax Return. Include copies of any schedules that have been changed or any Form W-2 (PDF) you did not include. The Form 1040X (PDF) should be submitted after you receive your refund or by the due date of the return, whichever, is earlier. Generally, to claim a refund, the Form 1040X (PDF) must be received within three years after the date you filed your original return or within two years after the date you paid the tax, whichever is later.

References:

• Tax Topic 308, Amended returns

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 file an amended or corrected return using Form 1040X (PDF), Amended U.S. Individual Income Tax Return, as soon as possible. Include copies of any schedules that have been changed or any Form W-2 (PDF) you did not include. If you return the refund check with a letter of explanation, a refund in the correct amount will be issued when the IRS processes the amended return.

References:

• Tax Topic 308, Amended Returns

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

References:

• Form 1040X Instructions
• Tax Topic 308, Amended Returns

You will need to contact our assistance line 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 12 to 16 weeks to process an amended return.

References:

• Form 1040X (PDF), Amended U.S. Individual Income Tax Return
• Tax Topic 308, Amended Returns

At this time, the Form 1040X is not accepted electronically.

References:

• Form 1040X Instructions
• Tax Topic 308