September 2026 Tax Deadlines for Businesses and Fiduciaries

September brings several critical tax compliance deadlines for businesses, ranging from extended returns for S corporations and partnerships to corporate estimated tax payments and employer payroll deposits. At Hays CPA LLC, we believe in providing our clients with the clarity and structure needed to navigate these obligations efficiently. Review the key due dates below to keep your filings and payments firmly on track.

Professional reviewing business compliance and tax deadlines

September 15: S Corporations

If you requested an automatic six-month extension for your S corporation, you must file your 2025 calendar year income tax return (Form 1120-S) and pay any remaining tax due. Additionally, you are required to provide each shareholder with a copy of their Schedule K-1 (Form 1120-S) or a substitute Schedule K-1, along with Schedule K-3 (Form 1120-S) or a substitute Schedule K-3, if applicable.

September 15: Corporations

Calendar year corporations must deposit their third installment of estimated income tax for the 2026 tax year.

September 15: Partnerships

Partnerships that timely requested an automatic six-month extension must file their 2025 calendar year return (Form 1065). You must also provide each partner with a copy of their Schedule K-1 (Form 1065) or a substitute Schedule K-1 and, where applicable, Schedule K-3 (Form 1065) or a substitute Schedule K-3.

September 15: Social Security, Medicare, and Withheld Income Tax

For employers subject to monthly deposit rules, this is the deadline to deposit Social Security, Medicare, and withheld income tax for August 2026. This date also applies to nonpayroll withholding deposits for August 2026 under the monthly deposit rule.

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September 30: Fiduciaries of Estates and Trusts

Fiduciaries granted a 5½-month extension must file their 2025 calendar year return (Form 1041). If applicable, you must also provide each beneficiary with a copy of their Schedule K-1 (Form 1041) or a substitute document.

Weekend and Holiday Rules

When a tax due date falls on a Saturday, Sunday, or legal holiday, the deadline is automatically extended to the next business day that is not itself a legal holiday.

Extensions for Disaster Areas

Due dates are often extended for taxpayers located in designated disaster areas. To verify if your geographic area qualifies for tax relief and to check specific extension dates, please consult the following resources:

Navigate Your Deadlines with Confidence

Managing strict tax deadlines doesn't have to be a source of stress. Whether you need assistance finalizing your extended 2025 returns or planning your 2026 estimated payments, the team at Hays CPA LLC is here to help you reduce tax liability and avoid surprises. Contact us to schedule a consultation and let our advisory team provide you with greater financial control.

Schedule an Appointment Today!
Please note appointments have a $75 booking fee that will apply as a credit on your invoice, if you choose to proceed with our services.
Book Here!
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