If a calendar-year C corporation that filed an automatic six-month extension:
File a 2019 income tax return (Form 1120) and pay any tax, interest and penalties due.
Make contributions for 2019 to certain employer-sponsored retirement plans.
Monday, November 2
Report income tax withholding and FICA taxes for third quarter 2020 (Form 941) and pay any tax due. (See exception below under “November 10.”)
Tuesday, November 10
Report income tax withholding and FICA taxes for third quarter 2020 (Form 941), if you deposited on time (and in full) all of the associated taxes due.
Tuesday, December 15
If a calendar-year C corporation, pay the fourth installment of 2020 estimated income taxes.
Thursday, December 31
Establish a retirement plan for 2020 (generally other than a SIMPLE, a Safe-Harbor 401(k) or a SEP).