When is the last day you can send in federal tax forms?

There are lots of federal tax forms..literally 1,000s, for different things.

However, virtually without exception, while they may have due dates after which a penalty MAY be applicable, you can file any of them late...even years late.

Individual Federal tax forms...commonly known as the Form 1040 series...are due anytime after the end of the year, but before April 15th (+ days if holiday or weekends), extensions may be granted (generally easily) and late filing is accepted, even without penalty IF, you have paid the tax due on the return by that due date. Just file the form and all support later.