A partnership return is generally due on the 15th day of the fourth month following the date its tax year ended. For a calendar year taxpayer this is April 15th. There is the ability to get an "automatic" additional 2 months to file the return (15th day of the sixth month) and if the partnership still needs additional time they must file a Form 7004 to request an additional three months. The return is late, even with extensions, if it is filed later than the 15th of the ninth month following the date its tax year ended. Again, for a calendar year partnership that makes the latest a properly extended tax return can be filed timely is 15 September (2013).