April 15 is the traditional due date for federal income taxes. It's a deadline so ingrained in the American psyche that the April 15 calendar date is often called, simply, "Tax Day".
In 2011, however, federal taxes aren't due April 15. They're due April 18. It's because of a combination of holiday, calendars, and tax law.
The change centers on Emancipation Day.
Emancipation Day is a public celebration in the District of Columbia. Named a holiday in 2005, Emancipation Day honors President Abraham Lincoln's April 16, 1862 signing of the Compensation Emancipation Act.
Emancipation Day is a non-working day in the nation's capitol but, this year, Emancipation Day falls on a Saturday. The municipality will observe the holiday Friday instead. This means that all of Washington, D.C. will be "closed" Friday, April 15 -- the usual tax filing deadline date.
This includes the IRS.
Therefore, to accommodate Emancipation Day, the government is extending this year's federal tax filing deadline to April 18, 2011. This year marks the second time Emancipation Day has forced the change of federal tax filing deadlines.
Also, as a non-related coincidence, tax filers in Georgia taking extensions to October 15 will also get a few extra days. October 15 is a Saturday so the extended tax deadline rolls over to the following Monday -- October 17, 2011.