CSC's friendly reminder for Taxpayer who have not yet filed their 2015 tax return that April 18, 2016 is the due date to either file your return and pay any taxes owed, or file for the automatic six-month extension and pay the tax you estimate to be due.Usually April 15 is the due date, but because Friday, April 15, is a legal holiday in the District of Columbia (where the IRS is headquartered), the filing date is advanced to the next day that isn ’t a weekend or holiday – Monday, April 18 – even for taxpayers not living in DC.