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.