The income tax return is due by the 15th day of the 4th month after the close of the tax year. Usually, this falls on April 15. If the due date falls on a Saturday, Sunday or legal holiday, the due date is delayed until the next business day. Extension filing gives you the extra time only to file your tax returns, in other words any tax dues must be paid on or before dude date. The extension form must be filed before the due date i.e. before April 15th, so that the tax payer gets the additional 6months time to file his tax return (Form 1040). Form 4868 gives an individual automatic extension of 6 months i.e. (April 15th + 6 months = Oct 15th). And filing Form 7004 gives a Company/Corporation/Partnership an additional extension of 6 months.