Form 1040 is the main form used to file personal income tax returns with the Internal Revenue Service. Tax returns are normally due on April 15th. Tax returns must be filed by anyone who might owe income taxes – for a single person, the threshold for 2020 is income of more than $12,400. Dependents with unearned income may also have to file a tax return, and other special circumstances exist. While Form 1040 is the main form used to file personal income tax returns, there is a version of the form, 1040-SR, designed for taxpayers over the age of 65.