November 1 – Social Security, Medicare and Withheld Income TaxFile Form 941 for the third quarter of 2021. Deposit or pay any undeposited tax under the accuracy of deposit rules. If your tax liability is less than $2,500, you can pay it in full with a timely filed return. If you deposited the tax for the quarter in full and on time, you have until November 10 to file the return.November 1 – Certain Small EmployersDeposit any undeposited tax if your tax liability is $2,500 or more for 2021 but less than $2,500 for the third quarter.November 1 – Federal Unemployment TaxDeposit the tax owed through September if more than $500.November 10 – Social Security, Medicare and Withheld Income TaxFile Form 941 for the third quarter of 2021. This due date applies only if you deposited the tax for the quarter in full and on time.November 15 – Social Security, Medicare and Withheld Income TaxIf the monthly deposit rule applies, deposit the tax for payments in October.November 15 – Nonpayroll WithholdingIf the monthly deposit rule applies, deposit the tax for payments in October.