October 2026 Business Tax Deadlines & Extension Guide

October brings a critical wave of tax deadlines for businesses and self-employed professionals. As the year progresses, it is essential to review upcoming filing dates, payroll tax deposit requirements, and retirement plan deadlines to determine which obligations apply to your organization.

Professional reviewing tax deadlines

October 15: Corporate Returns (Form 1120)

Corporations must file their 2025 calendar year income tax return using Form 1120 and remit any remaining tax, interest, and penalties due. Please note that this specific deadline applies only if your business timely requested an automatic six-month extension by April 15.

October 15: Social Security, Medicare, and Withheld Income Tax Deposits

For businesses subject to the monthly deposit rule, October 15 is the deadline to deposit taxes for payments made during September.

October 15: Nonpayroll Withholding Deposits

Similarly, if the monthly deposit rule applies to your nonpayroll withholding, you must deposit the tax for payments made in September by the October 15 deadline.

October 15: Establishing a Keogh Retirement Account

Self-employed individuals who received an automatic six-month extension of time to file their 2025 tax return have until October 15, 2026, to establish a Keogh Retirement Account, provided you intend to make a contribution for the 2025 tax year.

October 15: SEP IRA and Keogh Plan Contributions

October 15 also serves as the final day to make contributions to a SEP IRA or Keogh retirement plan for the 2025 calendar year, assuming your tax return is on extension through this date.

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Have questions about your taxes or business? Ara Haddadian, CPA, provides experienced tax and accounting services tailored to individuals and business owners. Visit [www.arahcpa.com](http://www.arahcpa.com) to learn more and request a consultation.
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Accounting for Weekends and Legal Holidays

When managing your tax calendar, remember that if a formal due date falls on a Saturday, Sunday, or legal holiday, the deadline is automatically extended. In these instances, your obligations are due on the next business day that is not itself a legal holiday.

Filing Extensions for Designated Disaster Areas

Businesses operating in regions designated as disaster areas often receive extended filing deadlines. To verify whether your specific geographical area has been declared a disaster zone and to confirm applicable extension dates, consult the following official resources:

Navigating Your October Tax Obligations

Missing an October tax deadline or extension requirement can lead to unnecessary penalties and interest. By proactively addressing these corporate filings, payroll deposits, and retirement plan deadlines, you protect your financial health. If you need assistance determining which deadlines apply to your operations or require support preparing your extended returns, schedule a consultation with our team today.

Learn more
Have questions about your taxes or business? Ara Haddadian, CPA, provides experienced tax and accounting services tailored to individuals and business owners. Visit [www.arahcpa.com](http://www.arahcpa.com) to learn more and request a consultation.
Schedule Consultation
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