September 17 - S Corporations
File a 2017 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. Provide each shareholder with a copy of K-1 (Form 1120S) or a substitute Schedule K-1.
September 17 - Corporations
Deposit the third installment of estimated income tax for 2018 for calendar year
September 17 - Social Security, Medicare and withheld income tax
If the monthly deposit rule applies, deposit the tax for payments in August.
September 17 - Nonpayroll Withholding
If the monthly deposit rule applies, deposit the tax for payments in August.
September 17 - Partnerships
File a 2017 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 17 - Electing Large Partnerships
File a 2017 calendar year return (Form 1065-B). This due date applies only if you were given a 6-month extension. March 15 was the due date for furnishing Schedules K-1 or substitute Schedule K-1 to the partners.
