February 23, 2026
2026 tax deadlines for Colorado small businesses
This year’s filing and estimated-tax dates, federal and Colorado, in one place — so the only surprise this tax season is how prepared you are.
A new year, the same job: know the dates and you avoid most penalty trouble. Here are the 2026 deadlines that matter for a Colorado small business. As always, when a date falls on a weekend or holiday it generally rolls to the next business day.
Filing deadlines
- March 15 — S-corporation and partnership returns are due (or file an extension). The one that sneaks up, a full month before personal returns.
- April 15 — personal and C-corporation returns are due, along with your Colorado individual return.
- September 15 — extended S-corp and partnership returns are due.
- October 15 — extended personal returns are due.
Remember: an extension buys time to file, not time to pay. If you will owe, pay by the original date to avoid interest.
Quarterly estimated taxes
The four 2026 estimate dates, for both federal and Colorado:
- April 15 (Q1)
- June 15 (Q2)
- September 15 (Q3)
- January 15, 2027 (Q4)
Our quarterly-estimates guide covers the safe-harbor rule that makes these penalty-proof if you hit the minimum on time.
The recurring filings
Around the big annual dates run the steady ones: payroll deposits and quarterly 941s, sales-tax returns (generally the 20th of the following month), and local filings like Denver’s OPT. They repeat all year, which is exactly why they are easy to drop.
A note for 2026
Start the year on the current numbers — wage rates, payroll-program parameters, and the sales-tax vendor-fee change all reset in January (we rounded those up in our guide to what’s changing in 2026). Setting your first-of-year payroll and sales-tax setup to the 2026 figures keeps small errors from compounding all year.
The surest way to never miss a date is to not have to remember them. If you would rather simply be kept ahead of all of it, that is a big part of what we do for clients.
This is general information for Colorado business owners, not individual tax advice, and dates shift for weekends and holidays. Confirm the current deadlines with the IRS and the Colorado Department of Revenue, or with a CPA.