Use Form 4868 to obtain a six-month extension for filing taxes by filing the form by the due date for your calendar year tax return or fiscal year return, explains the Internal Revenue Service. You are, however, not granted an extension to pay your tax liability.
When preparing and filing Form 4868, you must estimate how much you owe in taxes and pay the amount due, according to H&R Block. If you make a tax payment, include it in the payments section of your income tax form when filing. If you do not pay the full amount owed, you are assessed interest on the unpaid balance until you pay the balance in full. If you do not pay at least 90 percent of what you owe, you may also be assessed a late payment penalty, which can be half of 1 percent of the amount you owe for each month, up to a 25 percent maximum.
If you live abroad, you have two extra months to file your tax return and pay what you owe without the need to file an extension, states H&R Block. You must be out of the country on the filing due date and a resident alien or U.S. citizen to qualify for the two-month extension.