When are business tax returns due for 2026?

Partnership and S corporation returns are due March 15, 2026 with extensions to September 15. C corporation returns are due April 15 with extensions to October 15. Individual returns are due April 15 with extensions to October 15. The first quarter 2026 estimated tax payment is also due April 15.

What records should I keep from the 2025 tax year transition?

Keep documentation for all 2025 planning transactions including Roth conversions, estate tax gifts, income timing decisions, and retirement contributions. Accurately track basis in transferred assets and carryforward amounts for NOLs, capital losses, passive activity losses, and charitable contributions into 2026.

Filing Season 2026: Key Updates for Business Owners | Lynch Law

Filing Season 2026: Key Updates for Business Owners

Lynch Law, PLLC

The 2026 filing season brings the first tax returns prepared under whatever rate structure and rules emerged from the 2025 legislative process. Whether business owners are filing under extended TCJA provisions, new legislation, or reverted pre-2018 law, the filing season presents unique challenges that require early preparation and careful attention to the changed landscape.

Key Filing Deadlines

The filing deadline calendar remains consistent regardless of legislative changes. Partnership and S corporation returns (Forms 1065 and 1120-S) are due March 15, 2026, with a six-month extension available to September 15. C corporation returns (Form 1120) are due April 15, 2026, with a six-month extension to October 15. Individual returns (Form 1040) are due April 15, 2026, with a six-month extension to October 15. The first quarter estimated tax payment for 2026 is also due April 15.^[1]

New Forms and Changed Schedules

Legislative changes typically result in new or revised IRS forms and schedules. Business owners should work with their tax preparers early in the filing season to identify any new reporting requirements. If the Section 199A deduction expired, Form 8995 (used to calculate the qualified business income deduction) would no longer be required. If new provisions were enacted, new forms may be needed. Changes to the standard deduction, personal exemptions, and rate brackets will all be reflected in the 2026 tax tables and withholding schedules.^[2]

Record Keeping and Documentation

The 2025 tax year may have been the last year under TCJA rules, making accurate record keeping for the transition particularly important. Business owners should ensure they have documentation for any 2025 planning transactions (Roth conversions, estate tax gifts, income acceleration or deferral decisions, and retirement plan contributions). The basis in assets transferred during 2025 and the carryforward amounts from prior years (NOLs, capital loss carryforwards, passive activity loss carryforwards, and charitable contribution carryforwards) must be accurately tracked into 2026.^[3]

State Tax Filing

Mississippi tax filing deadlines and requirements may also have changed for 2026. Business owners should verify the Mississippi individual and corporate income tax filing deadlines, any changes to Mississippi tax rates or deductions, the status of any pass-through entity tax elections, and the franchise tax filing requirements for entities registered with the Secretary of State.^[4]

Early preparation is the key to a smooth filing season. Business owners should gather their records, schedule a meeting with their tax advisor, and begin the return preparation process well before the filing deadlines to allow time for planning decisions that can still be made during the return preparation process (such as retirement plan contributions and accounting method elections).^[5]

References

^[1] IRC §§ 6072, 6081 (filing deadlines and extension rules for partnership, S corporation, C corporation, and individual income tax returns).
^[2] IRS forms and schedules are revised annually to reflect legislative changes; new provisions may require new reporting forms.
^[3] Accurate tracking of basis, carryforward amounts, and transition-year transactions is essential for proper 2026 return preparation.
^[4] Mississippi individual and corporate income tax requirements; franchise tax filing for entities registered with the Secretary of State.
^[5] See Tax Controversy & IRS Defense (discussing filing season preparation and tax return compliance).

This article is for informational purposes only and does not constitute legal advice. The facts of every situation are different, and you should consult with a qualified attorney before taking action based on the information in this article.