Most individuals of legal age know April 15 as the date that taxes are due. But, when are they not due on April 15?

Before the Revolutionary War, taxes were mostly on whiskey and tobacco. During the Civil War, the federal government tried to collect taxes, but it was eventually declared unconstitutional.

On July 2, 1909, Congress passed and, on Feb. 3, 1913, the 16th Amendment was ratified and added to the U.S. Constitution.

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The 16th Amendment gave Congress the legal authority to tax the income of the people, establishing the individual income tax.

The deadline in 1913 was March 1. The deadline changed to March 15 in 1918 and, since 1955, the deadline has been April 15.

So, when are taxes due now and why? The answer is, “It depends!”

Until 2011, the Patriot's Day holiday in Maine and Massachusetts sometimes gave residents of those states, and states mailing returns or payments to the federal government with addresses in those states an extra day if the 15th fell on the holiday. The IRS, for the most part, has resolved that issue by no longer having payments sent to addresses in those states.

If the 15th falls on Monday, Tuesday, Wednesday or Thursday, taxes are due on that day. If the 15th falls on a Saturday, Sunday or holiday, they are due on the next day that is NOT a Saturday, Sunday or holiday.

Here is where it gets a little tricky. In 1862, President Lincoln signed the District of Columbia Compensated Emancipation Act for the release of certain persons held to service or labor in the District of Columbia. The District of Columbia celebrates April 16 as Emancipation Day. This holiday is celebrated on different dates, in different parts of the country. On Jan. 4, 2005, the D.C. mayor signed legislation making Emancipation Day an official holiday in D.C. So, while Emancipation Day occurs on April 16, by law, when April 16 falls during a weekend, the holiday is observed on the nearest weekday.

So if the 15th falls on a Friday, it is the nearest weekday to the holiday on the 16th and that pushes the 15th tax deadline to Monday the 18th. If the 15th falls on a Saturday, that means the 16th, which falls on a Sunday, gets pushed to the closest weekday, Monday the 17th, and taxes are not due until Tuesday the 18th. If the 15th falls on a Sunday, then Monday the 16th is the scheduled holiday and it pushes the tax filing deadline to Tuesday the 17th, as it does this year.

If even with the two extra days, you find that you still can’t put your hands on that W-2 or a 1099, you can file and ask for an extension by the due date on form 4868. Please know that the extension is only an extension of time to submit the paperwork, not an extension of time to pay the tax. You should estimate as conservatively close as you can and submit payment in full with the extension form. The extension gets you six months extra and the return is then due on Oct. 15.

If you are located outside of the 50 states, D.C. and Puerto Rico, your due date is generally two months later, on June 15.

Lynn Rendine is a certified public accountant. She has been practicing for more than 35 years, with an office and practice in Yorktown Heights. She can be reached at 914-245-5966.