Tax season in the United States requires careful planning. Missing a deadline can result in penalties from the IRS. We've compiled all the important dates for 2025–2026 into one convenient calendar.
Important date-shifting rule: If a filing deadline falls on a weekend or federal holiday, it automatically moves to the next business day.
Core Deadlines
January 15, 2026
Q4 2025 estimated tax for individuals (Form 1040-ES).
March 16, 2026
Filing of returns or extension for partnerships (Form 1065) and S-corporations (Form 1120-S) for tax year 2025.
April 15, 2026
- Form 1040 / 1040-NR for 2025 (filing and payment or extension)
- Form 1120 for 2025 (filing and payment or extension)
- Q1 2026 estimated tax
June 15, 2026
Q2 2026 estimated tax. For nonresidents, specific payment dates are outlined in Form 1040-ES(NR) instructions.
September 15, 2026
- Q3 2026 estimated tax
- Extended deadline for Form 1065/1120-S (if extended)
October 15, 2026
Extended deadline for Form 1040, 1040-NR, and 1120 (if extended).
December 15, 2026
Fourth quarterly estimated tax payment for corporations.
State Requirements: Delaware, Wyoming, California
Delaware
- C-Corp Annual Report + Franchise Tax: due by March 1 each year
- LLC/LP/GP Annual Tax ($300): due by June 1 each year
Wyoming
- Annual Report: floating deadline — the 1st day of the anniversary month of the company's registration. For example, if the company was registered on May 15, the annual report must be filed by May 1 each year.
California (FTB)
- CA LLC annual tax ($800): 15th day of the 4th month after the start of the tax year (for calendar year — typically April 15)
- CA LLC fee (if applicable): estimated payment by the 15th day of the 6th month; final calculation due with the tax return
- Return due dates: depend on entity type — 15th day of the 3rd or 4th month after year-end; extension typically to the 9th/10th/11th month
How to Avoid Missing Deadlines
- Use a calendar: Add all relevant dates to Google Calendar or Outlook with reminders set 2–4 weeks in advance
- Request extensions early: Even if you can't file your return on time, an extension gives you additional time (but doesn't extend the tax payment deadline)
- Pay estimated tax on time: Late payments lead to underpayment penalties
- Monitor state requirements: Delaware, California, and other states have their own deadlines that don't align with federal dates
Conclusion
The US tax calendar is a complex system of federal and state deadlines. Pay close attention to dates, especially if you have multiple businesses or entities in different states. When necessary, consult with a tax professional to avoid penalties and properly plan your tax payments.
This article is for informational purposes only and does not constitute tax advice. For decisions regarding your specific situation, please book a free consultation with Konstantin.
