The return is due March 15 for the previous year. Your S-corp doesn't pay taxes, it files a form 1120S informational return. The 1120S produces a form k-1 that states your share of the companies income and other items. You report that k-1 on Schedule E of your Form 1040 in April. You have to file the 1120S every year whether you made money or not. Definitely find a professional, the 1120S is not easy to do.