What should I do if I discover a mistake on a tax return I've already filed?

Use Form 1040X, Amended U.S. Individual Income Tax Return, to correct errors or omissions on your original return. Filing Form 1040X may result in an additional tax refund or liability. For example, if you discovered that you should have included $1,000 from free-lance work on your 2003 income tax return, you should file Form 1040X for 2003 to include the $1,000 value in your income.

When you file an amended return, be sure to use the tax law, rules, rates, and schedules for the tax year being amended.