September 2026 Business Tax Due Dates: Extended Returns and Estimates

September brings several critical tax deadlines for businesses. Depending on your entity structure, this month may require you to file extended returns for S corporations and partnerships, remit corporate estimated tax payments, or fulfill employer payroll tax deposits. At Midwest Tax Resolution, LLC, we understand that managing these requirements can be stressful, especially for busy operators. Review the key due dates below to ensure your business filings and payments remain on track.

Tax compliance and accounting due dates

September 15: S Corporations

If your S corporation requested an automatic six-month extension, you must file your 2025 calendar year income tax return (Form 1120-S) and pay any outstanding tax due by September 15. Alongside the corporate return, you are required to provide each shareholder with a copy of their Schedule K-1 (Form 1120-S) or a substitute Schedule K-1. If applicable to your business, you must also provide Schedule K-3 (Form 1120-S) or its substitute.

September 15: Corporations

Calendar year corporations must deposit the third installment of their 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) by September 15. You must provide each partner with a copy of their Schedule K-1 (Form 1065) or a substitute Schedule K-1. Additionally, if it applies to your entity, provide Schedule K-3 (Form 1065) or a substitute Schedule K-3.

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

If you are an employer subject to the monthly deposit rules, September 15 is the deadline to deposit your Social Security, Medicare, and withheld income taxes for August 2026. This date also serves as the deadline for the nonpayroll withholding deposit for August 2026, provided the monthly deposit rule applies.

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We’ve helped countless individuals and businesses get back on track with the IRS. Reach out today for a confidential consultation and start moving toward financial relief.
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September 30: Fiduciaries of Estates and Trusts

If you were granted a 5½-month extension, you must file the 2025 calendar year return (Form 1041) for estates and trusts by September 30. Where applicable, fiduciaries must provide each beneficiary with a copy of their Schedule K-1 (Form 1041) or a suitable substitute.

Weekend and Holiday Rules

Standard IRS allowances apply to these deadlines: if a due date happens to fall on a Saturday, Sunday, or legal holiday, your filing or payment is automatically extended to the next business day that is not a legal holiday.

Disaster Area Extensions

If your business is located in a geographical region designated as a disaster area, your due dates will generally be extended. To verify whether your specific area qualifies for relief and to review updated filing extension dates, visit the following official resources:

Maintain Your Business Compliance This Fall

Missing a deadline can trigger stressful complications and unneeded attention from the IRS or state authorities. Timely filing and payments are your best defense against future compliance issues. If your business has fallen behind on payroll deposits, income tax returns, or is facing collection actions, Midwest Tax Resolution, LLC is here to help. Contact our Carmel, Indiana office today to schedule a consultation and take a decisive step toward resolving your tax problems equitably.

Take Control of Your Tax Situation
We’ve helped countless individuals and businesses get back on track with the IRS. Reach out today for a confidential consultation and start moving toward financial relief.
Contact Us
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