You should file an amended return if your filing status, your dependents, your total income or your deductions or credits were reported incorrectly. In addition, things like getting amended Form 1099s, or Form K-1s from partnerships, estates and trusts would trigger the need to amend the return.
When Should You Not Amend
In some cases, you do not need to amend your tax return. The IRS usually corrects math errors or requests missing forms - such as W-2s or schedules - when processing an original return. In these instances, do not amend your return.
What Form Should Be Used: Form 1040X
Use Form 1040X, Amended U.S. Individual Income Tax Return, to amend a previously filed Form 1040, 1040A or 1040EZ. Make sure you check the box for the year of the return you are amending on the Form 1040X. Amended tax returns cannot be filed electronically.
What Should You Do If You Are Amending Multiple Years
If you are amending more than one year's tax return, prepare a 1040X for each return and mail them in separate envelopes to the appropriate IRS processing center.
Some Hints On Completing Form 1040X
The Form 1040X has three columns. Column A shows original figures from the original return. Column C shows the corrected figures. The difference between Column A and C is shown in Column B. There is an area on the back of the form to explain the specific changes and the reason for the change. Be sure to be clear and detailed as to these details on the back page so as to maximize your chances of successfully filing this amended return.
Attachments Must Be Part of the Amended Return
Be sure to attach to the Form 1040X other forms or schedules, if the changes involve other schedules or forms.
Refund Claim Still Pending From Original Return: Wait To Receive It Before Filing Form 1040X
If you are filing to claim an additional refund, wait until you have received your original refund before filing Form 1040X. Once you receive that check, you may cash it while waiting for any additional refund that may come from the filing of Form 1040X.
Additional Taxes Due As the Result of Filing Form 1040X
If you going to owe additional tax, you should file Form 1040X and pay the tax as soon as possible to limit interest and penalty charges.
When Must You File Form 1040X For a Refund
Generally, to claim a refund, you must file Form 1040X within three years from the date you filed your original return or within two years from the date you paid the tax, whichever is later.
What is the Normal Processing Time
Usually the processing time for amended returns is 8 to 12 weeks.