Colorado biennial assessment cycle: how appeals work

Last updated 2026-07-10

What is Colorado's biennial assessment cycle?

Colorado assessors revalue every property once every two years, always in odd-numbered years (2023, 2025, 2027). The rule comes from Colorado Revised Statutes Section 39-1-104, which sets the odd year as the 'assessment year' and locks that value in for the next two tax years. ^[1]

Assess your home in 2023 and that value drives your 2023 and 2024 bills. The next full revalue hit in 2025 and governs 2025 and 2026 taxes. Nobody applies for the cycle. It resets on its own.

The date that controls everything is June 30 of the year before the assessment year. Colorado calls it the 'appraisal date.' Your 2025 value reflects market conditions as of June 30, 2024, and nothing after. That single fact decides which comparable sales you can use, because sales that closed after the appraisal date usually don't count in an appeal. ^[1]

Assessors mail Notice of Valuation (NOV) postcards by May 1 of the assessment year. The card shows your new value next to the old one. Keep it. The protest deadline is printed right there, and blowing that deadline forfeits your appeal rights for the whole two-year cycle.

When exactly are the appeal deadlines in Colorado?

The protest deadline under C.R.S. 39-5-122 is June 8 of the odd assessment year. If June 8 lands on a Saturday, Sunday, or legal holiday, it moves to the next business day. ^[2]

Colorado runs two separate appeal stages, each with its own clock:

Stage	Who hears it	Deadline to file	Decision by
Assessor protest (informal)	County Assessor	June 8 of assessment year	June 30 of assessment year
County Board of Equalization (CBOE)	County commissioners sitting as CBOE	July 15 (or 30 days after assessor's decision if later)	Aug. 5 of assessment year
State Board of Assessment Appeals (BAA)	Independent state board	30 days after CBOE decision	Varies; hearing scheduled
District Court or binding arbitration	Court or arbitrator	30 days after CBOE decision	Varies

Miss June 8 and the informal stage is gone. The CBOE clock starts when the assessor mails its decision, so watch your mail in late June. ^[3]

Here's what catches people: the deadline is for filing, not for receiving the NOV. If your postcard gets lost in the mail, the clock still runs from May 1, the date they were required to mail it. Check your assessor's website in early May instead of trusting the Postal Service.

How does the assessor protest (informal appeal) work?

The assessor protest is your first shot and, for most homeowners, the easiest one. You file straight with your county assessor: online, by mail, or in person, depending on the county. Nearly every Colorado county now takes online protests through a county form or the state's mass-appraisal portal. ^[4]

Your protest has to state why the value is wrong. C.R.S. 39-5-122(1) recognizes three grounds: the value is too high, the property is classified wrong, or the record has an error (wrong square footage, wrong lot size, a bathroom that doesn't exist). Name a specific dollar value you think is correct and back it with evidence. That beats 'this feels too high' every time.

Submit your evidence with the form. What actually helps:

• Recent sales of genuinely comparable homes (closed within 12 months before June 30 of the prior year, same neighborhood, similar size and condition).
• A recent appraisal, if you got one from a purchase or refinance.
• Photos of physical defects or condition problems the assessor never saw.
• The assessor's own property record card, marked up where the data is wrong.

The assessor has until June 30 to send a written decision. They can lower the value, keep it, or raise it. A raise is legal but rare. Get the number you want and you're done. If not, you go to the CBOE.

What happens at the County Board of Equalization (CBOE)?

The CBOE is the formal step. In most counties the board is the county commissioners acting in a quasi-judicial role; a few large counties use hearing officers. You present your case in person or by video, the assessor's office presents theirs, and the board rules. ^[3]

File your CBOE petition by July 15, or within 30 days of the assessor's decision, whichever is later. Get the petition form from the county clerk or assessor. Bring everything you gave the assessor, plus a rebuttal to whatever reason they cited when they denied you.

Hearings run short. Fifteen to thirty minutes is typical. Prepare a one-page summary: your property's key facts, your three to five best comps in a clean table, and the value you're asking for. Board members aren't appraisers. Clarity beats volume.

The CBOE must decide by August 5. Win, and the assessor fixes the record. Lose, and you have three roads: the state Board of Assessment Appeals, district court, or binding arbitration. All three require filing within 30 days of the CBOE decision. ^[3]

For a residential property at or under $1 million in actual value, binding arbitration through the county is often cheaper and faster than the BAA. The BAA makes more sense for high-value property, for a real legal question (more than a number fight), or when you want a written decision on the record.

What evidence actually wins a Colorado property tax appeal?

Assessors use mass appraisal. They run statistical models across thousands of properties at once. The model is fine on average and wrong on individual homes often enough to matter, especially homes with odd features, condition problems, or those sitting in a micro-neighborhood that doesn't move with the broader market.

The strongest evidence in a Colorado residential appeal is a tight set of comparable sales. The Division of Property Taxation publishes the Assessors' Reference Library, and its comp standards track normal appraisal practice: sales within one mile or the same neighborhood, similar size (within 15 to 20 percent of gross living area), closed within 12 months before the June 30 appraisal date. ^[5]

Pull comps from free sources: Zillow's sold filter, Redfin, county public records, or the public MLS tools some title companies offer. Three good comps beat ten weak ones.

Photos win condition arguments. Roof at the end of its life, cracked foundation, a furnace from 1987, photograph all of it and get a written repair estimate from a licensed contractor. Assessors don't walk through individual homes. They lean on permit records and drive-by looks. They have no idea your boiler is shot.

Wrong data on your record card is the cleanest win of all. An extra bathroom, or 200 square feet you don't have, can swing the value several thousand dollars. Measure, document, and pull your property record card from the assessor's website or counter before you file. It's public record.

Want a structured way to pull this together? The TaxFightBack DIY appeal kit walks through the Colorado evidence checklist and a comparable-sales grid so you keep every dollar of any reduction instead of splitting it with a contingency firm.

How does Colorado calculate assessed value from market value?

Colorado doesn't tax your home at full market value. It applies an assessment rate to get the assessed value, then the mill levy applies to that. ^[6]

The residential assessment rate ran at 7.15% for years. Legislation passed in 2023, including SB23-108, temporarily dropped it to 6.765% for tax years 2023 and 2024, with more adjustments in the works. Nonresidential property sits at 29%. These rates move with the legislature, so confirm the current number with the Division of Property Taxation or your county assessor before you finalize any appeal math. ^[6][7]

Here's the arithmetic. A $500,000 home at a 6.765% rate has an assessed value of $33,825. At 80 mills (0.080), the tax bill is $2,706. Knock $50,000 off market value and you save about $270 a year at that levy. Real money, not life-changing, on a single-family home. The big wins come from large overassessments, classification errors, or commercial property, where the 29% rate multiplies every dollar you take off the value.

So classification is worth a hard look. If any slice of your property is tagged commercial, or an accessory dwelling unit got misclassified, fixing it can beat a straight value protest by a wide margin.

Can you appeal in an even year when there's no new assessment?

Usually no. Colorado's two-year cycle means assessors mail no new NOVs in even years and open no standard protest window. The odd-year value governs both years.

The exceptions are narrow. Under C.R.S. 39-5-125, an assessor can change an even-year value if there was an error in the odd-year assessment, if the property changed (addition, demolition, subdivision), or if new construction finished. ^[11] In those cases the assessor issues a corrected or supplemental NOV, and a fresh protest window opens with it.

If your property was destroyed or badly damaged, you can also apply for a pro-rated reduction under C.R.S. 39-1-104.2 for the part of the year the property wasn't usable.

Otherwise, miss the June 8 deadline in the assessment year, or lose your CBOE appeal without pursuing it further, and your next opening is the following odd-year cycle. That's two full tax years paying on a value you think is wrong. That's the whole reason June 8 matters as much as it does.

What if you missed the June 8 protest deadline?

Missing June 8 hurts, but it isn't always the end. A few paths remain.

First, if you never got the NOV, some counties accept a late protest with an affidavit stating you received no notice. It's discretionary and not a sure thing, but worth an immediate call to the assessor.

Second, check whether any even-year exception under C.R.S. 39-5-125 fits your property. A recent renovation, a boundary change, or a data correction can open a new window. ^[11]

Third, some counties allow abatement and refund petitions under C.R.S. 39-10-114 when you can show the assessment was erroneous or illegal. These go to the county commissioners, not the assessor, and you have two years from the tax levy to file. They're tough to win on pure valuation, but worth a shot when the overassessment is large and the regular window has closed. ^[8]

Fourth, if the assessor made a procedural mistake (wrong appraisal date, wrong classification as a matter of law), the BAA and district courts have occasionally taken jurisdiction even after the administrative deadlines passed. That's genuinely rare, and you'd want an attorney to make the argument.

How do Colorado assessment appeals compare to other states?

Colorado's biennial cycle is unusual. Most states reassess every year, so homeowners get a new protest window annually. A handful, like Cook County, Illinois (reassessed on a three-year rotation), also stretch out the schedule, but two-year cycles paired with a strict appraisal-date rule aren't the norm. ^[9]

The appraisal-date rule (June 30 of the prior year) is stricter than most. California is a different animal entirely: Proposition 13 caps annual increases at 2% until the property changes hands, so the appeals dynamic there barely resembles Colorado's. Cook County uses current sales up through the filing date. Compare notes with an out-of-state friend and check that the evidence rules match before you copy their playbook.

Colorado's two administrative stages (assessor, then CBOE) before you reach the BAA or court are fairly standard. Plenty of states make you exhaust administrative remedies before a judge will look at the case.

One place Colorado leans homeowner-friendly: the burden of proof. At the CBOE, C.R.S. 39-8-107 puts the initial burden on the assessor to establish that the valuation is correct, and the taxpayer then rebuts. In practice, a well-documented protest with solid comps can move the number without any elaborate legal argument. ^[12]

To see how different county processes run, look at how cook county tax assessor tax bill or hennepin county property tax handle their own cycles.

What happens after you win (or lose) your Colorado appeal?

Win at the assessor or CBOE stage and the assessor fixes the record, with the new value flowing to your December tax notice. You file nothing more. The correction is automatic.

If you already paid the current year's taxes (Colorado's first installment is due February 28, the second April 30, on the prior year's levy), a reduction produces a credit or refund. Timing depends on when the adjustment finalizes and how your county handles it. Some cut refund checks, others credit the next bill.

Lose at the CBOE and want to keep going? You have three options within 30 days: the BAA, district court, or arbitration. The BAA is an independent state board that hears both sides de novo, meaning it weighs the evidence fresh rather than deferring to the CBOE. Its decisions can go up to the Court of Appeals. BAA hearings are more formal, but most homeowners with a clean valuation case handle themselves fine. A complex commercial case or a legal classification fight may call for a pro.

Binding arbitration under C.R.S. 39-8-108.5 is open to residential properties at actual value of $1 million or less, plus most other property types. The arbitrator's ruling is final. No appeal. It's faster than the BAA and usually cheaper, but you give up every further option. ^[3]

For how appeal outcomes flow into the tax bill in other large jurisdictions, the montgomery county property tax guide and the la county property tax piece cover similar post-appeal mechanics.

Is it worth appealing your Colorado property tax assessment yourself?

For most homeowners, yes. The assessor protest costs nothing, needs no attorney, and takes one to two hours to prepare well. Cut your assessed value by $30,000 and, at a typical Colorado residential mill levy (roughly 50 to 120 mills depending on county and special districts), you save about $100 to $240 a year. Because the reduction holds for two years, that's $200 to $480 over the cycle.

Contingency firms usually take 25 to 40 percent of the first year's savings, sometimes up to 50 percent. On $300 of first-year savings, that's $75 to $150 handed over for work you could finish in an afternoon.

When does professional help earn its keep? Commercial property above $1 million, income-approach valuation questions (apartments, retail centers), or a legal fight over classification. For those, a property tax attorney or a fee-based appraiser whose report you own outright beats a contingency firm.

The TaxFightBack appeal kit hands you the Colorado forms guide, a comparable-sales worksheet, and a hearing-prep checklist so you walk in organized instead of winging it. You keep 100% of what you save.

Here's the honest read on DIY: the process is built for property owners to use themselves. The Division of Property Taxation publishes plain-language guides. County assessors run help lines. The evidence rules aren't hard. Homeowners who put in two or three hours and show up with three good comps usually get at least some reduction.

Frequently asked questions

When does Colorado mail assessment notices in 2025?

Colorado county assessors must mail Notice of Valuation postcards by May 1, 2025, under C.R.S. 39-5-121. Because 2025 is an odd year, it starts a new two-year cycle, and every residential and commercial property gets a fresh value. Watch your mail in late April and early May. If nothing shows, check your assessor's website or call, because the protest clock runs from the May 1 mailing date no matter what.

What is the protest deadline for Colorado property taxes in 2025?

June 8, 2025. That's the statutory deadline under C.R.S. 39-5-122 to file your informal protest with the county assessor. If June 8 falls on a weekend or holiday, it moves to the next business day. Miss it and you lose the informal stage, which as a practical matter shrinks your options for the entire two-year cycle down to narrow exceptions.

What is the appraisal date Colorado assessors use, and why does it matter?

For the 2025 assessment year, the appraisal date is June 30, 2024. Colorado assessors must value property at market value as of that exact date under C.R.S. 39-1-104. So your comparable sales should have closed on or before June 30, 2024. Sales from July 2024 onward generally won't be accepted as direct comps, though they can support a market-trend argument in unusual conditions.

How do I find my Colorado property's assessed value versus market value?

Your Notice of Valuation shows both. The 'actual value' (sometimes called market value) is what the assessor thinks your property would sell for. The 'assessed value' is actual value times the assessment rate (6.765% residential in 2025, 29% commercial, subject to legislative change). Your tax bill is assessed value times your total mill levy. You can also pull both numbers from your county assessor's public records portal using your parcel number.

Can I appeal in an even year in Colorado?

Rarely. The biennial system means no new NOV in even years and no standard protest window. The exceptions are narrow: a corrected notice after the assessor finds an error, new construction finished in the even year, a change in property characteristics (demolition, subdivision), or substantial damage. Outside those, if you missed the odd-year deadline or lost your appeal, the next chance is the following odd-year cycle. An abatement petition under C.R.S. 39-10-114 is a limited backstop for clear errors.

What is the Colorado Board of Assessment Appeals (BAA)?

The BAA is an independent state administrative court that hears property tax appeals after the County Board of Equalization process. It sits under the Colorado Department of Local Affairs. Hearings are more formal than the CBOE: both sides present evidence and can call witnesses. You must file within 30 days of your CBOE decision. BAA rulings can be appealed to the Colorado Court of Appeals. For most residential cases, the BAA is the last realistic step short of district court.

How long does a Colorado property tax appeal take?

The informal assessor protest is quick. You file by June 8, the assessor must answer by June 30. Proceed to the CBOE and hearings happen in July with decisions by August 5. Appeal to the BAA and the timeline stretches. Backlogs have historically meant waits of six months to over a year for a hearing date, though the board has been working to shorten them. District court takes longer still. Arbitration is usually the fastest route to finality after the CBOE.

Does filing a protest risk raising my Colorado property tax assessment?

Technically yes, in practice almost never. Under C.R.S. 39-5-122, an assessor can raise a value during the protest. But assessors rarely do this in response to a homeowner protest, because the hassle outweighs any small revenue gain. The far more likely outcome is a reduction or a confirmation of the existing value. Commercial owners with clearly underassessed property face a slightly higher, still small, risk.

What is a good success rate for Colorado property tax appeals?

There's no reliable statewide success-rate figure across all counties and property types. The Division of Property Taxation tracks appeals filed and decided but doesn't publish a uniform win rate. County-level data suggests well-documented protests with valid comparable sales get at least a partial reduction a meaningful share of the time, but the range is wide, driven by how well you prepare and how hot the local market has run.

Do I need an attorney or appraiser to appeal my Colorado property taxes?

For most residential appeals, no. The assessor protest and CBOE process is built for self-represented owners. A licensed appraiser's report adds credibility but costs $300 to $600 or more for a residential property, so it only pays off when your likely savings clear that cost. An attorney is worth considering for high-value commercial property, classification disputes, or BAA and court proceedings where procedure matters. For standard residential overassessments, good comps and a clear written argument usually do the job.

How does Colorado's biennial cycle compare to annual reassessment states?

In annual states, a missed deadline costs you one year, not two, because a fresh protest window opens every year. Colorado's two-year cycle raises the stakes on each window. The flip side: win a reduction and you get two years of lower taxes from one appeal. California runs on completely different rules (Prop. 13 caps annual increases at 2%), which makes Colorado's market-value biennial system more volatile but also easier to correct when the market moves.

How do I get my Colorado property record card to check for errors?

Property record cards are public records. Most Colorado counties post them online through the assessor's property search portal, searchable by address or parcel number. If yours has no online access, request it in person or by email from the assessor at no charge. The card lists the characteristics behind your value: square footage, bedroom and bathroom count, year built, condition rating, and lot size. Any error in those is grounds for a protest.

What is binding arbitration in a Colorado property tax appeal, and when should I use it?

Binding arbitration under C.R.S. 39-8-108.5 lets a neutral arbitrator settle the dispute after you've exhausted the CBOE. The decision is final; no further appeal. It's open to most property types and is usually faster and cheaper than the BAA or district court. Use it when the dollar amount doesn't justify a long BAA proceeding and you trust your evidence. Skip it if you have a novel legal argument, because the arbitrator's decision creates no precedent.

Sources

1. Colorado General Assembly, C.R.S. 39-1-104 (Assessment date; legislative declaration): Colorado requires biennial revaluation of real property in odd-numbered years with an appraisal date of June 30 of the prior year
2. Colorado General Assembly, C.R.S. 39-5-121 and 39-5-122 (Notice of valuation; protest deadline of June 8): Assessors must mail NOVs by May 1; taxpayers must file protests by June 8 of the assessment year
3. Colorado Division of Property Taxation, County Board of Equalization Reference Manual: CBOE petitions due July 15 or 30 days after assessor decision; CBOE must decide by August 5; further appeals must be filed within 30 days; arbitration available under C.R.S. 39-8-108.5
4. Colorado Division of Property Taxation, Taxpayer Appeal Rights Guide: Taxpayers may file assessor protests online, by mail, or in person; protest must state grounds and evidence
5. Colorado Division of Property Taxation, Assessors' Reference Library (Appraisal Manual): Colorado assessors use comparable sales within the neighborhood, similar size, and sold within 12 months before the June 30 appraisal date
6. Colorado Division of Property Taxation, Assessment Rates and Mill Levies: Residential assessment rate reduced to 6.765% for tax years 2023-2024; nonresidential rate 29%, subject to legislative change
7. Colorado General Assembly, SB23-108 (Property Tax Exemption Relief): SB23-108 and related 2023 legislation temporarily reduced the residential assessment rate and capped assessment value growth
8. Colorado General Assembly, C.R.S. 39-10-114 (Abatement and refund of taxes): Abatement and refund petitions may be filed within two years of tax levy for erroneous or illegal assessments
9. Lincoln Institute of Land Policy, Significant Features of the Property Tax (State-by-state reassessment frequency data): Most U.S. states reassess annually; Colorado's biennial cycle is atypical nationally
10. Colorado Department of Local Affairs, Board of Assessment Appeals: BAA is an independent state administrative court hearing property tax appeals after CBOE; decisions appealable to the Colorado Court of Appeals
11. Colorado General Assembly, C.R.S. 39-5-125 (Even-year corrections by assessor): Assessors may issue corrected or supplemental NOVs in even years for errors, new construction, or changes in property characteristics
12. Colorado General Assembly, C.R.S. 39-8-107 (Burden of proof in appeals): Assessor bears initial burden of establishing correctness of valuation at CBOE level; taxpayer may then rebut