There's nothing more annoying than filing your income tax return and then discovering that you made an error or omission. When this happens, you must file an amended tax return showing the error. Amended returns can be prepared for returns filed as far back as three years. Unlike current tax returns, they cannot be filed electronically.
Download a copy of IRS Form 1040X from of the IRS website. This form may also be available at your public library or you can call the IRS at (800) 829-1040 and have them send you a copy.
Use your original tax return as a reference to begin completing the 1040X. You will need to transpose all of the information from your original return that is correct onto the 1040X and then list the error or errors and the numerical impact they have on your return. You will need to explain the nature and amount of the error on the form in the prescribed area.
Provide backup documentation for all of your changes in the form of receipts, ledgers, income statements, etc. Be prepared for the possibility that this return will be audited, because amended returns are always processed by IRS employees and not by computer.
Submit your amended return to the IRS either by mail or in person at your local IRS office. If you deliver your return personally, the IRS will give you back a stamped copy that serves as proof of filing. Send your return via certified mail if you choose this path, so that someone at the IRS has to sign for it when it arrives, thus furnishing you with proof that your return was received.
Amend your state tax returns as well, if necessary. Each state will have its own amended tax return form. In many cases, this form is identical to the usual tax form, except that you must check a box indicating that the return is amended.