Here are a few key tax-related deadlines for businesses and other employers during the second quarter of 2017. APRIL 18: If calendar-year C corporation, file or extend 2016 income tax return and pay any tax due, and pay first installment of 2017 estimated taxes. MAY 1: Report income tax withholding and FICA taxes for first quarter 2017 (unless eligible for exception). JUNE 15: If calendar-year corporation, pay second installment of 2017 estimated income taxes. Contact us for more about the filing requirements and to ensure you’re meeting all applicable deadlines.