Soon after the passing of the 16th Amendment, Congress named March 1, 1914 as the first Tax Day. Why March 1? It fell roughly one year after the 16th Amendment was enacted [source: Sung]. The Bureau of Internal Revenue created Form 1040 to file and pay personal income tax, which was 1 percent for income under $3,000 ($4,000 for married joint filers) and up to 6 percent for the wealthiest Americans [source: Tax History Museum].
Tax Day was moved to March 15 in 1918 and then again to April 15 in 1955. The official reason for the pushback was to spread the workload of IRS employees, but some economists speculate that a later filing date means the government can wait even longer to pay refunds [source: Sung]. The longer the IRS can hold onto the money it withholds via payroll taxes, the more interest it earns.
But even the April 15 due date can shift a little. In 2005, the District of Columbia enacted Emancipation Day on April 16 to commemorate the day Lincoln signed an 1862 law freeing the first slaves in Washington, D.C. When April 16 falls on a Saturday, the holiday is officially celebrated on Friday, and when it falls on Sunday, it's celebrated on Monday. The IRS can't force people to file taxes on a holiday (even a local one) or the weekend. That's why Tax Day became Monday, April 18 in 2011, because Friday the 15th was technically Emancipation Day. If April 15 is a Sunday and Emancipation Day falls on a Monday, Tax Day will be Tuesday, April 17 -- for everyone.
There's a small caveat, however: If you submit IRS Form 4868 on or before April 15, you get an automatic six-month filing extension. But that doesn't mean you don't have to pay any taxes you owe by April 15. According to the IRS, you need to estimate what you owe (this year's W-2 forms and last year's return should give you an idea) and pay that amount on April 15. If you pay too much, the IRS will refund you the difference when you file. If you pay too little, you can make up the difference when you file. But if you don't pay anything, the IRS will charge interest (plus a late payment penalty) on what you owe starting on April 16 [source: IRS].
For lots more information on taxes and the IRS, see the related links on the next page.