when is form 1120 s due 
form 1120 s is the annual tax return for s corporations it must be filed with the irs by the 15th of the third month following the end of the corporation s tax year 1 so if a company s tax year runs from jan 1 to dec 31 the company s tax return is due on march 15 on the other hand a company whose tax year runs between july 1 and june 30 must complete and file form 1120 s by sept 15 the bottom lineevery entity must report its tax liabilities by filing a tax return each year with the irs this includes individuals and businesses of all sizes form 1120 s is the return that is dedicated to s corporations these businesses have fewer than 100 shareholders and pass their income and losses to each shareholder companies can file these forms electronically or by mail and must include schedule k 1 with their returns all paperwork must be submitted to the irs by the 15th of the third month after the end of the corporation s tax year 