1. You did not report some income,

2. You claimed deductions or credits you should not have claimed,

3. You did not claim deductions or credits you could have claimed, or

4. You should have claimed a different filing status. (Once you file a joint return, you cannot choose to file separate returns for that year after the due date of the return. However, an executor may be able to make this change for a deceased spouse.)

Form 1040X

Use Form 1040X, Amended U.S. Individual Income Tax Return, to correct a return you have already filed. An amended tax return cannot be filed electronically under the e-file system.

Completing Form 1040X. On Form 1040X, write your income, deductions, and credits as you originally reported them on your return, the changes you are making, and the corrected amounts. Then figure the tax on the corrected amount of taxable income and the amount you owe or your refund.

If you owe tax, pay the full amount with Form 1040X. The tax owed will not be subtracted from any amount you had credited to your estimated tax.

If you cannot pay the full amount due with your return, you can ask to make monthly installment payments. See Installment Agreement, earlier.

If you overpaid tax, you can have all or part of the overpayment refunded to you, or you can apply all or part of it to your estimated tax. If you choose to get a refund, it will be sent separately from any refund shown on your original return.

Filing Form 1040X. After you finish your Form 1040X, check it to be sure that it is complete. Do not forget to show the year of your original return and explain all changes you made. Be sure to attach any forms or schedules needed to explain your changes. Mail your Form 1040X to the Internal Revenue Service Center serving the area where you now live (as shown in the instructions to the form). However, if you are filing Form 1040X in response to a notice you received from the IRS, mail it to the address shown on the notice.