Individuals. If you have an automatic six-month extension to file your income tax return for 2017, file Form 1040, 1040A, or 1040EZ and pay any tax, interest, or penalties due.
Employers. For Social Security, Medicare, withheld income tax, and nonpayroll withholding, deposit the tax for payments in September if the monthly rule applies.
Corporations. File a 2017 calendar-year income tax return (Form 1120) and pay any tax, interest, and penalties due. This due date applies only if you timely requested an automatic 6-month extension.
Employers. For Social Security, Medicare, and withheld income tax, file Form 941 for the third quarter of 2018. Deposit any undeposited tax. (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.
For federal unemployment tax, deposit the tax owed through September if more than $500.