The following tax returns are due today:
Partnerships: Form 1065 (or Form 7004 for a 6-month extension).
S-corporations: Form 1120S (or Form 7004 for a 6-month extension).
Please note that this applies to calendar year filers only. If your year end is not December 31st, you are a fiscal year filer and your due date is different.
For partnerships and S-corporations that are fiscal year filers, the due date is the 15th day of the 3rd month following the close of the tax year.