Monday, September 16th, 2019

Individuals: If you are not paying your 2019 income tax through withholding (or you will not pay enough tax during the year that way), pay the third installment of your 2019 estimated tax by this date. You can use IRS Form 1040-ES (Estimated Tax for Individuals). For more information, see IRS Publication 505 (Tax Withholding and Estimated Tax).

Partnerships: If you obtained a 6-month tax extension, your 2018 tax return (IRS Form 1065) is due by this date. Otherwise, see March 15. You must also provide each partner with a copy of their final/amended Schedule K-1 (Form 1065) or substitute Schedule K-1.

S Corporations: If you obtained a 6-month tax extension, your 2018 tax return is due by this date. File IRS Form 1120S and pay any tax, interest, and penalties due. Otherwise, see March 15. You must also provide each shareholder with a copy of their final/amended Schedule K-1 (Form 1120S) or substitute Schedule K-1.

Corporations: Make the third installment payment for 2019 estimated income tax. You can use the worksheet, IRS Form 1120-W (Estimated Tax for Corporations), to help you calculate your estimated tax for the year.