Critical IRS deadlines March 9, 2020 Accounting, News, SoundCPA Insights Partnerships and Corporations: Critical IRS deadlines to keep in view as we navigate turbulent times. Monday March 16, 2020 For many businesses, this is a critical due date for changes and elections. Businesses taxed as partnerships file 2019 tax returns with IRS by Monday March 16, 2020. Businesses taxed as S-corporations file 2019 tax returns with IRS and pay any tax due by Monday March 16. Wednesday, April 15, 2020 Businesses taxed as C-corporations file 2019 tax returns and pay any tax due by Wednesday, April 15. Share