Things to Remember When Amending a Tax Return

Filing Form 1040X is not enough. Along with the form, you must include the form affected by the change and the supporting documentation. For example, if you forgot to deduct a certain business expense on Schedule C, you must complete a corrected Schedule C along with Form 1040X. At the time of publication, you can't submit the amendment electronically. You must mail the forms to the Internal Revenue Service.

Use the appropriate forms for the year. If you are amending a return from 2010, use the 2010 version of Form 1040X and follow the specific instructions for that year. You can find forms and instructions from prior years on the IRS website. If you are amending multiple returns, mail each form in a separate envelope. You can file amendments within three years of the original filing date or two years after paying your taxes, whichever date is later.

When your federal tax liability changes, it may trigger a change in your state taxes as well. Your state tax office can provide information on correcting your state return. Make copies of any supporting evidence you include in the federal amendment since you will likely need to submit the same documents with your state tax correction.

Wait to file the amended return until your original return is processed. Filing too soon can create confusion and delays. If you are anticipating an additional refund, wait until you have received your original refund before submitting the corrections. You don't have to wait until the amendment is processed to cash your refund. However, if the correction leads to a lower refund, set some of it aside to pay back the money right away. According to the IRS, the average processing time for amended returns is eight to 12 weeks.