September 16 - S Corporations
File a 2018 calendar year income tax return (Form 1120S) and pay any tax due. This due date applies only if you requested an automatic 6-month extension. Provide each shareholder with a copy of K-1 (Form 1120S) or a substitute Schedule K-1.
September 16 - Corporations
Deposit the third installment of estimated income tax for 2019 for calendar year
September 16 - Social Security, Medicare and withheld income tax
If the monthly deposit rule applies, deposit the tax for payments in August.
September 16 - Non-payroll Withholding
If the monthly deposit rule applies, deposit the tax for payments in August.
September 16 - Partnerships
File a 2018 calendar year return (Form 1065). This due date applies only if you were given an additional 5-month extension. Provide each partner with a copy of K-1 (Form 1065) or a substitute Schedule K-1.
September 30 - Fiduciaries of Estates and Trusts
File a 2018 calendar year return (Form 1041). This due date applies only if you were given an extension of 5 1/2 months. If applicable, provide each beneficiary with a copy of K-1 (Form 1041) or a substitute Schedule K-1.