The deadline to file the Partnership 1065 and S Corporation 1120S tax returns is September 15, one month before the extended personal 1040 deadline of October 15. This assumes that a timely extension was filed on or before March 15. The 1065 and 1120S are information tax returns, no tax is due with these returns. Typically, a K1 is issued, which reports income and expenses to the individual partners or shareholders. This is referred to as “flow through” taxation.

The penalties are steep for not filing timely. They are $250 per month, per partner ir shareholder. By October 2, there would be two penalty assessments, so if there are 4 partners, the penalty would be $2,000 on October 2. This can quicky add up and become a material, nondeductible expense for small businesses.

The September 15 cannot be extended.