Individual tax returns are due April 18th, as Saturday, April 16, 2016 is Emancipation Day in the District of Columbia, and the holiday is observed on Friday, April 15th. However, because Patriot's Day will be observed on April 18 in Maine and Massachusetts, residents of those states will have until April 19th to file and pay their taxes.
This also means that by statute you have until April 18th to amend a 2012 return to claim a refund.
A nonresident alien completing a Form 1040NR generally needs to file by June 15th. However, nonresident aliens who have wages paid in the United States or receive non-employee compensation in the United States need to file by April 18th.