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Key September 2026 Tax Deadlines for Businesses

As a business owner, September brings a fresh wave of critical tax deadlines. Whether you are filing an extended return for an S corporation or partnership, managing corporate estimated tax payments, or keeping up with employer payroll deposits, staying ahead of these dates is essential. At TaxDrx, our goal is to help you maintain clarity and peace of mind by keeping your business filings and payments on track. Review the key due dates below.

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September 15: S Corporations

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

September 15: Corporations

For calendar year corporations, this is the deadline to deposit the third installment of your 2026 estimated income tax.

September 15: Partnerships

If you timely requested an automatic six-month extension, your 2025 calendar year return (Form 1065) is due. Additionally, provide each partner with a copy of their Schedule K-1 (Form 1065) or a substitute, and Schedule K-3 (Form 1065) or a substitute if applicable.

September 15: Payroll and Withholding Deposits

If you are an employer and the monthly deposit rules apply, you must make your deposit of Social Security, Medicare, and withheld income tax for August 2026 by this date. This is also the due date for the nonpayroll withholding deposit for August 2026 under the monthly deposit rule.

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September 30: Fiduciaries of Estates and Trusts

File a 2025 calendar year return (Form 1041). This due date applies only if you were given an extension of 5½ months. If applicable, provide each beneficiary with a copy of their Schedule K-1 (Form 1041) or a substitute Schedule K-1.

Weekends and Holidays

If any 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.

Disaster Area Extensions

Please note that when a geographical area is designated as a disaster area, due dates will be extended. To verify whether your area has been designated as a disaster area and to check specific filing extension dates, visit the following resources:

FEMA: https://www.fema.gov/disaster/declarations
IRS: https://www.irs.gov/newsroom/tax-relief-in-disaster-situations

Keep Your Business Compliant and Forward-Focused

Managing compliance alongside daily operations can feel overwhelming, but staying ahead of these September deadlines protects your cash flow and peace of mind. If you need help navigating these filings or want to explore proactive tax savings strategies, the team at TaxDrx is here for you. Contact our Cranford, New Jersey office or schedule a virtual consultation today to simplify your financial life.

Schedule a Complimentary Consultation
Choose from our locations and meet with one of our qualified staff members. If you prefer to secure a Virtual Meeting via Zoom or Phone, please contact our offices at 877.908.1040
Schedule Here
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