What are the penalties for paying my personal taxes late?

Late payment penalties apply if you don't pay taxes owed by the due date of your tax return, usually April 15th, unless it falls on a Saturday, Sunday or holiday.   If you file your return or an extension, any taxes you owe are due on by the deadline of April 15th.  Filing an extension gives you more time to prepare and file your return, not more time to pay any taxes owed.

The late payment penalty is 0.5% (1/2 of 1 percent) of the additional tax owed amount for every month (or fraction thereof) the owed tax remains unpaid, up to a maximum of 25%.