- If a calendar-year C corporation that filed an automatic six-month extension:
- File a 2016 income tax return (Form 1120) and pay any tax, interest and penalties due.
- Make contributions for 2016 to certain employer-sponsored retirement plans.
- Report income tax withholding and FICA taxes for third quarter 2017 (Form 941) and pay any tax due. (See exception below.)
- Report income tax withholding and FICA taxes for third quarter 2017 (Form 941), if you deposited on time and in full all of the associated taxes due.
- If a calendar-year C corporation, pay the fourth installment of 2017 estimated income taxes.