What is the purpose of an amended income tax form?

Mistakes made when filing a tax return may require filing an amended income tax form, states the IRS. Changes in filing status, income, deductions or credits require an amended return. Mathematical errors may be corrected without the need for an amended return.

State returns may be affected by changes made to a federal return, notes the IRS. It suggests contacting state tax agencies to resolve any needed corrections.

The Form 1040X instructions contain information on where it can be mailed to amend a U.S. individual tax return. As of July 2015, amended tax returns cannot be filed using the IRS e-file system, according to the IRS.