(MEDIA GENERAL) – The old saying, “nothing can be said to be certain, except death and taxes” doesn’t really ring true, considering Tax Day – which usually falls on April 15 – has been delayed to April 18 (or April 19) in 2016.

No, the IRS wasn’t feeling especially kind, giving everyone a few extra days to file.

There’s a legitimate reason for the switch that’s pretty interesting, if not a little confusing.Washington celebration benefits all

A little-known holiday outside of Washington, D.C., Emancipation Day is the primary reason for changing the tax deadline, says the US Tax Center.

While slavery was not formally abolished in the United States until Dec. 6, 1865, when the 13th Amendment was ratified, it occurred in the District of Columbia much earlier.

President Abraham Lincoln signed the Compensated Emancipation Act on April 16, 1862, freeing thousands of slaves living in the district.

Now a legal holiday in Washington, government offices and other public services do not operate on Emancipation Day, usually celebrated April 16.

However, if April 16 falls on a weekend, as it does this year, it is celebrated on the closest weekday – that way public workers still get a day off of work. So this year, it moves to April 15, Tax Day.

Since Emancipation Day is a legal holiday, it takes precedence over the tax deadline, which must then be moved to the following business day, Monday, April 18.Maine, Massachusetts’ extra extension

Maine and Massachusetts residents get an additional deadline extension because of another relatively unknown holiday – Patriots’ Day.

A legal holiday in Massachusetts (and Maine, which was once part of the Commonwealth) since 1969, Patriots’ Day commemorates the Battles of Lexington and Concord, the first battles in the Revolutionary War.

Patriots’ Day is celebrated on the third Monday in April, which happens to be April 18, giving citizens an optional filing extension to April 19.

But there’s one caveat: because Maine and Massachusetts residents send their returns to an IRS facility in another state where Patriots’ Day is not observed, they are required to submit the first installment of their estimated income tax payment by April 18 for it to be considered timely, according to the IRS.

Because of that, Bay Staters might be better off filing alongside everyone else on April 18.

Still haven’t filed? Click here for tax filing tips.