September 15 – Corporations
File a 2015 calendar year income tax return (Form 1120 or 1120-A) and pay any tax, interest, and penalties due. This due date applies only if you timely requested an automatic 6-month extension.
September 15 – S Corporations
File a 2015 calendar year income tax return (Form 1120S) and pay any tax due. This due date applies only if you requested an automatic 6-month extension.
September 15 – Corporations
Deposit the third installment of estimated income tax for 2016 for calendar year corporations.
September 15 – Social Security, Medicare and withheld income tax
If the monthly deposit rule applies, deposit the tax for payments in August.
September 15 – Nonpayroll Withholding
If the monthly deposit rule applies, deposit the tax for payments in August.
September 15 – Partnerships
File a 2015 calendar year return (Form 1065). This due date applies only if you were given an additional 5-month extension. Provide each partner with a copy of K-1 (Form 1065) or a substitute Schedule K-1.
September 15 – Fiduciaries of Estates and Trusts
File a 2015 calendar year return (Form 1041). This due date applies only if you were given an additional 5-month extension. If applicable, provide each beneficiary with a copy of K-1 (Form 1041) or a substitute Schedule K-1.