IRS Form 1040X is the Amended United States Individual Tax Return. It is used to make corrections on to a previously filled tax returns using either Form 1040, Form 1040A, or Form 1040EZ. Generally Form 1040X must be filed within three years after the original form was filed or within two years after the tax was paid for a tax refund. A 1040X that is filed immediately before the due date of the original form is considered on time.

The IRS Form 1040X is similar to Form 1040 except that it has three columns. The first column is for listing the amounts from the original form, the second column is for listing the net increase or decrease for each changed line, and the third column is for listing the new amounts.

Generally, a taxpayer should only file an amended return to correct filing status, total income, tax deductions, or tax credits. There is no need to file an amended return to correct math errors as the IRS computers will check the math and correct any errors in calculation.

Certain type of changes cannot be made with Form 1040X and must be requested through the much more complicated IRS Form 3115 "Change of Accounting Method". The form lists over 50 specific change types that require its use, many including classic bookkeeping concerns, such as when to recognize revenue and expenses.

You can download IRS Form 1040X here.