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September 2026 Business Tax Due Dates to Keep on Your Radar

September brings a wave of important tax deadlines for business owners across Scottsdale, Denver, and Albuquerque. From extended returns for S corporations and partnerships to corporate estimated tax payments and employer payroll deposits, staying organized is essential. At GeneralCents Accounting, your BackPocket CFO, we want to ensure you have the key dates you need to keep your filings and payments perfectly on track.

Tax compliance tools

September 15 Tax Deadlines

Extended S Corporation Returns

If you requested an automatic six-month extension for your S corporation, your 2025 calendar year income tax return (Form 1120-S) is due. You must also 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) if that applies to your business.

Corporate Estimated Tax Payments

For calendar year corporations, September 15 marks the deadline to deposit the third installment of your 2026 estimated income tax.

Extended Partnership Returns

Partnerships that timely requested an automatic six-month extension must file their 2025 calendar year return (Form 1065). Additionally, you are required to provide every partner with a copy of their Schedule K-1 (Form 1065) or a substitute, as well as Schedule K-3 (Form 1065) if applicable.

Payroll and Nonpayroll Withholding Deposits

If you are an employer subject to the monthly deposit rules, you must make your deposit for Social Security, Medicare, and withheld income tax for August 2026. This is also the due date for the August 2026 nonpayroll withholding deposit, provided the monthly deposit rule applies.

September 30 Fiduciary Deadlines

Estates and Trusts

If you serve as a fiduciary of an estate or trust and were granted a 5½-month extension, your 2025 calendar year return (Form 1041) is due. If applicable, you must also provide each beneficiary with a copy of their Schedule K-1 (Form 1041) or a substitute version.

Weekend, Holiday, and Disaster Considerations

Weekends and Legal Holidays

If any tax due date happens to fall on a Saturday, Sunday, or legal holiday, the IRS automatically extends the deadline to the next business day that is not a legal holiday.

Disaster Area Tax Relief

When a geographical area is officially designated as a disaster area, tax due dates are typically extended. To verify if your region qualifies for this relief and to find specific filing extension dates, check the following official resources:

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

Keep Your Business Compliant and Prepared

Missing a tax deadline can create unnecessary headaches, but tracking these dates keeps your operations running smoothly. If you need help managing these filings, reaching out to a professional is the smartest move.

Contact John Koloch at GeneralCents Accounting today to discuss your tax situation and explore how our BackPocket CFO services can support your business.

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