September 11

Employees Who Work for Tips – If you received $20 or more in tips during August, report them to your employer. You can use Form 4070.

September 15

Individuals – Make a payment of your 2017 estimated tax if you are not paying your income tax for the year through withholding (or will not pay in enough tax that way). Use Form 1040-ES. This is the third installment date for estimated tax in 2017.

Partnerships – File a 2016 calendar year income tax return (Form 1065). This due date applies only if you were given an additional 6-month extension. Provide each shareholder with a copy of Schedule K-1 (Form 1065) or a substitute Schedule K-1.

S corporations – File a 2016 calendar year income tax return (Form 1120S) and pay any tax due. This due date applies only if you made a timely request for an automatic 6-month extension. Provide each shareholder with a copy of Schedule K-1 (Form 1120S) or a substitute Schedule K-1.

Electing Large Partnerships – File a 2016 calendar year income tax return (Form 1065-B) and pay any tax due. This due date applies only if you timely requested an automatic 6-month extension. Otherwise, see March 15. Provide each partner with a copy of Schedule K-1 (Form 1065-B) or a substitute Schedule K-1.

Corporations – Deposit the third installment of estimated income tax for 2017. A worksheet, Form 1120-W, is available to help you make an estimate of your tax for the year.

Employers – Nonpayroll withholding. If the monthly deposit rule applies, deposit the tax for payments in August.

Employers – Social Security, Medicare, and withheld income tax. If the monthly deposit rule applies, deposit the tax for payments in August.