Individuals: If you are not paying your 2016 income tax through withholding (or will not pay in enough tax during the year that way), pay the third installment of your 2016 estimated tax. Use IRS Form 1040-ES.
Employers: For Social Security, Medicare, withheld income tax, and nonpayroll withholding, deposit the tax for payments in August if the monthly rule applies.
Corporations: File a 2015 calendar-year income tax return (IRS Form 1120) and pay any tax, interest, and penalties due. This due date applies only if you timely requested an automatic six-month extension.
Deposit the third installment of estimated income tax for 2016. Use the worksheet IRS Form 1120-W to help estimate tax for the year.
S corporations: File a 2015 calendar-year income tax return (IRS Form 1120S) and pay any tax due. This due date applies only if you timely requested an automatic six-month extension. Provide each shareholder with a copy of Schedule K-1 (IRS Form 1120S) or a substitute Schedule K-1.