What should I do if I made a mistake on my federal return that I have already filed?

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.