Here are the important tax and compliance deadlines for September 2021.

In September, it’s recommended that you:
Schedule appointments for for year-end tax planning sessions.
Remember the extended October 15 filing deadline for 2020 returns for individuals and C corporations, and for calendar-year S corporations and partnerships that obtained automatic extensions.
Key Compliance Dates:
Wednesday, September 1 – Semiweekly depositors deposit FICA and withheld income tax on wages paid on August 25–27.
Friday, September 3 – Semiweekly depositors deposit FICA and withheld income tax on wages paid on August 28–31.
Thursday, September 9 – Semiweekly depositors deposit FICA and withheld income tax on wages paid on September 1–3.
Friday, September 10:
Semiweekly depositors deposit FICA and withheld income tax on wages paid on September 4–7.
Tipped employees who received $20 or more in tips during August report them to the employer on Form 4070, Employees Report of Tips to Employer.
Wednesday, September 15:
Monthly depositors deposit FICA and withheld income tax for August.
Semiweekly depositors deposit FICA and withheld income tax on wages paid on September 8–10.
Individuals and calendar-year corporations pay third installment of 2020 estimated tax.
Calendar-year S corporations file 2020 income tax return (Form 1120S, U.S. Tax Return for an S Corporation) if an automatic extension was obtained.
Partnerships file 2020 Form 1065, U.S. Return of Partnership Income, if automatic extension was obtained.
Friday, September 17 – Semiweekly depositors deposit FICA and withheld income tax on wages paid on September 11–14.
Wednesday, September 22 – Semiweekly depositors deposit FICA and withheld income tax on wages paid on September 15–17.
Friday, September 24 – Semiweekly depositors deposit FICA and withheld income tax on wages paid on September 18–21.
Wednesday, September 29 – Semiweekly depositors deposit FICA and withheld income tax on wages paid on September 22–24.
Resources:
The September 2021 calendar with filing deadlines and reminders.