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. However, you should file an amended return if any of the following were reported incorrectly:
Your filing status
Your total income
Your deductions or credits
Use IRS Form 1040X, Amended U.S. Individual Income Tax Return, to correct a previously filed Form 1040, 1040A, 1040EZ or electronically-filed return. Be sure to enter the year of the return you are amending at the top of Form 1040X. If you are amending more than one tax return, prepare a 1040X for each return and mail them in separate envelopes to the IRS processing center for the area in which you live. The 1040X instructions list the addresses for the centers.
If you are filing to claim an additional refund, wait until you have received your original refund before filing Form 1040X. You may cash that check while waiting for any additional refund. If you owe additional tax for 2007, you should file Form 1040X and pay the tax by the April due date to avoid any penalty and interest.
Generally, 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, to claim a refund.