Can’t finish your federal income tax return by the April deadline? Requesting an extension to shift the due date to October 17, 2016, takes three steps. First, estimate your 2015 tax liability. Second, enter that number on the extension request form (Form 4868). Third, file Form 4868 by the regular due date of your return. You can request the extension on paper, by phone, or online. Be aware that an extension doesn’t give you more time to pay the tax you owe.