What Happens If You Don't File Your Taxes or an Extension by April 15?

Will you be penalized for filing late? Here's what we know. The clock is ticking. You need to file your tax return or an extension by the April 15 deadline.  The big day is almost here. Tax Day is April 15 for most Americans but if you live in one of the states with automatic extensions, you have a little more time. If not and you don't file an extension or complete your tax return by midnight on Monday, you'll be delinquent.