The IRS form 1040 is the primary tax document that most taxpayers will need to file annual individual income tax returns. Generally, the 1040 tax form details a taxpayer’s taxable income, the amount of taxes they are required to pay, the amount they already paid, and any remaining balance they either still owe or the government owes them.

There are four versions of the 1040 form, and many individuals will need to attach other documents to explain the calculations and figures. For instance, the Schedule 1 tax form references additional income not typically reported on the 1040 and deductions to income that reduce the taxpayers’ total tax responsibility.