Travis Bunn
Founder, AppealDesk · Published February 28, 2026 · Updated August 21, 2026
The 2026 filing window closed on June 8, 2026. The rule is June 8, so the next deadline is June 8, 2027. Use the time before it opens to build the evidence.
Check your property now, $49 flat fee →Knowing your deadline is half of it. The other half is whether the county’s number is actually too high, because a deadline you meet with no case is just paperwork. Checking your number is free and takes about a minute.
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Updated August 2026
Colorado has one protest deadline, and it is the same in every county: your objection to the assessor must be postmarked or delivered by June 8. The window opens May 1, when Notices of Valuation go out. If you have seen pages claiming some counties use May 1 and others June 15, that split does not exist in Colorado law; the dates that matter are May 1 (window opens), June 8 (protest deadline), and then September 15 if you take a denial to the county board.
Reading this in late August 2026? The June 8 protest deadline has passed, but if you protested and were denied, your Notice of Determination arrived around mid-August and your County Board of Equalization appeal is due September 15. That clock is running right now.
A missed protest deadline in Colorado is not the end of the road. If you did not object by June 8, you can petition for an abatement or refund under C.R.S. 39-10-114 after the taxes are levied, by contacting your county assessor. It is a slower path and it starts after the bill exists rather than before, but it is the legislature's own second chance for owners who missed the protest window, and it can reach back to correct an erroneous valuation.
Colorado values property from a statutory base period, not from whatever sold last month. Sales that closed after the base period ends can be dismissed no matter how similar the homes are. Before you lean on a recent sale, confirm it falls inside the period your county's notice cites; boards deny otherwise-good cases on this point.
Knowing the date is the easy part. The date only matters if the county's number is actually too high, and nobody checks that number for you.
The number your appeal would challenge, pulled free in seconds. No account needed.
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Solution: Show the ordinance change and its value impact
A real AppealDesk order, Denver County
In May 2026, a homeowner in Denver County ran the check. The county had their home on record at $2,387,100, while recorded sales of comparable homes supported about $1,600,198: an over-assessment of $786,902, worth roughly $4,244 per year if corrected. Their packet laid out the comparable sales, the forms, and the filing steps. Nobody at the county was ever going to run that check for them.
A deadline you meet with no evidence behind it is just paperwork. Comparable sales are what boards actually respond to, and pulling your county's number is where that starts.
Enter your address to pull your county record free. If it looks too high, your $49 packet gives you the comparable sales, forms, and filing steps.
Colorado's protest deadline is June 8, statewide, no county exceptions. The window opens May 1, the assessor answers by mid-August, and a denial can go to your County Board of Equalization until September 15. Miss June 8 and the abatement petition is the honest fallback.
With Colorado's wildfire, water, and mountain-access complexities, successful appeals come down to in-period comparable sales and documented property facts. Know the three dates, and build the evidence before the window opens.
Statutory basis: C.R.S. 39-5-122 (protest to the assessor by June 8), C.R.S. 39-10-114 (abatement petitions). Confirm hearing logistics and filing methods with your county assessor.