October 1 - Fiduciaries of Estates and Trusts

File a 2017 calendar year return (Form 1041). This due date applies only if you were given an extension of 5 ½ months. If applicable, provide each beneficiary with a copy of K-1 (Form 1041) or a substitute Schedule K-1.

October 15 - Corporations

File a 2017 calendar year income tax return (Form 1120 or 1120-A) and pay any tax, interest, and penalties due. This due date applies only if you timely requested an automatic 6-month extension.

October 15 - Taxpayers with Foreign Financial Interests

If you received an automatic 6-month extension of time to report your 2017 foreign financial accounts to the Department of the Treasury, this is the due date for Form FinCEN 114.

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

October 15 - Nonpayroll Withholding

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

October 31 - Social Security, Medicare and Withheld Income Tax

File Form 941 for the third quarter of 2018. 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 13 to file the return.

October 31 - Certain Small Employers

Deposit any undeposited tax if your tax liability is $2,500 or more for 2018 but less than $2,500 for the third quarter.

October 31 - Federal Unemployment Tax

Deposit the tax owed through September if more than $500.