Federal income taxes are usually due on the 15th of April, unless that day falls on a weekend or federal holiday, which bumps the due date to the next business day.
Aside #15: The 15th of April is not the Ides of April. Lots of people have heard the warning, "Beware the Ides of March," from Shakespeare's Julius Caesar. Those people can be forgiven for thinking that the Ides of every month is on the 15th, as it is in March. But those people don't have the friends I do, and so they don't know that the Ides is only on the 15th in March, May, July, and October. In all other months the Ides is on the 13th.Since the 15th of April (17 days before the Kalends of May) falls on a Sunday you'd also be justified in thinking that taxes were due on the 16th. In fact, the IRS thought that was the due date when they printed this year's forms.
But there is another rule which says that taxes cannot be due on a holiday celebrated in the District of Columbia. Guess what? Today (16 days before the Kalends of May) is a holiday in my birthplace, Washington, D.C. It is Emancipation Day. Therefore, taxpayers across this great land are allowed to mail their tax returns (or applications for an extension) on the 17th and still be counted as on-time.
Don't believe me? Check out the following (poorly worded) posting on the IRS website: