September 2021 Business Due Dates

September 15 – S Corporations

File a 2020 calendar year income tax return (Form 1120-S) and pay any tax due. This due date applies only if you requested an automatic 6-month extension. Provide each shareholder with a copy of their Schedule K-1 (Form 1120-S) or a substitute Schedule K-1.

September 15 – Corporations 

Deposit the third installment of estimated income tax for 2021 for calendar year

September 15 –  Social Security, Medicare and Withheld Income Tax

If the monthly deposit rule applies, deposit the tax for payments in August.

September 15 – Nonpayroll Withholding

If the monthly deposit rule applies, deposit the tax for payments in August.

September 15 – Partnerships

File a 2020 calendar year return (Form 1065). This due date applies only if you were given an additional 5-month extension. Provide each partner with a copy of K-1 (Form 1065) or a substitute Schedule K-1.

September 30 – Fiduciaries of Estates and Trusts

File a 2020 calendar year return (Form 1041). This due date applies only if you were given an extension of 5 1/2 months. If applicable, provide each beneficiary with a copy of K-1 (Form 1041) or a substitute Schedule K-1.