Here are a few key tax-related deadlines for businesses and other employers during Quarter 4 of 2020. OCT. 15: If you’re the owner or operator of a calendar-year C corp. which filed an extension, file a 2019 income tax return. NOV. 2: Report income tax withholding and FICA taxes for Q3 2020 (unless you’re eligible for a Nov. 10 deadline because you deposited on time (and in full) all of the associated taxes due). DEC. 15: If a calendar-year C corp., pay the fourth installment of 2020 estimated income taxes. Contact us for more about the filing requirements and to ensure you’re meeting all applicable deadlines.