Monday, September 17th, 2018

Personal - Pay the third installment of their 2018 estimated income tax.

Corporations - If you recieved a six-month extension from March 16, send in your 2017 calendar-year tax return (Form 1120 or 1120-A) and pay any tax that is due. Also, pay the third installment of 2018 estimated income tax.

S Corporations - If you recieved a six-month extension from March 16, send in your 2017 calendar-year tax return (Form 1120s)

Partnerships (and LLCs treated as partnerships) - If you recieved a five-month extension from April 15, send in your 2017 calendar-year tax return. Provide each partner with a copy of Schedule K-1 (Form 1065).

Employers - August 2018 payroll tax deposit due if you're not on a semiweekly deposit schedule.