Boulder County, CO Property Tax Appeal Guide for 2027

What deadline matters first

For Boulder County real property, the expected regular 2027 protest window is May 1, 2027 through June 8, 2027. Plan for online, faxed, or emailed submissions to be in by 11:59 p.m. Mountain Time on June 8, 2027. Boulder County’s published real property appeal page says real property appeals are filed with the Assessor from May 1 through June 8, and the county calendar says online and faxed appeals must be time-stamped by 11:59 p.m. on June 8 to be on time (Boulder County Assessor appeals, Boulder County appeals calendar).

File early if you can. A filing problem close to the deadline may be hard to fix, and Boulder County states that deadlines are strictly enforced.

The first filing is with the Boulder County Assessor’s Office. If you file on time and later disagree with the Assessor’s decision, the next local appeal body is the Board of Equalization (BOE). Boulder County explains that the BOE is separate from the Assessor’s Office and schedules hearings for property owners who disagree with the Assessor’s valuation (Boulder County Board of Equalization).

For planning only, this page uses an approximate Boulder County effective tax rate of 0.62%. That means a $10,000 value change might roughly affect annual taxes by about $62 before any individual tax-area differences. Your actual bill can differ because Boulder County taxes depend on actual value, assessment rates, mill levies, and the taxing districts for your property (Boulder County tax calculation).

A historical volume example may help you see that appeals are not unusual. A public meeting summary reported that the Boulder County Assessor received 7,802 real property appeals in 2025 and adjusted roughly 40% of them, which is a useful appeal count reference but not a promise about any individual result (Citizen Portal meeting summary).

The common value appeal

The common value issue for a homeowner is “Property Value is too high.” Use that official reason when comparable sales support a lower actual value than the value shown by Boulder County.

For the 2027 assessment, the market level is measured as of June 30, 2026. The primary comparable-sales period is July 1, 2024 through June 30, 2026. Boulder County’s assessment materials explain that Colorado real property is revalued in odd-numbered years, uses a 24-month base period, and uses June 30 of the year before the reappraisal year as the official appraisal date (Boulder County assessment and valuation).

In plain English, you are trying to show what your home would reasonably have sold for at the county’s required valuation date. A good filing does not just say the increase feels too large. It gives your opinion of value and points to similar sales that support it.

Other reasons you might appeal

Boulder County’s official appeal reasons include more than a high-value concern. Preserve the label that fits your situation.

“Property Value is too low” means the evidence supports a higher actual value than the county listed. Most homeowners trying to reduce a bill will not choose this reason, but it is an official local category.

“Property Record is Incorrect” means the county is using wrong facts about your property. Examples include incorrect finished square footage, basement finish, bedroom or bath count, lot size, condition, or improvements. This reason is often supported with photos, measurements, permits, floor plans, contractor records, or other documents.

“Classification is Incorrect” means the property has been assigned the wrong assessment classification. Classification is the legal category used for assessment purposes, such as the way the property is used. Boulder County states that property owners may appeal assessed value or classification (Boulder County Assessor appeals).

If your Notice of Assessment says something else changed

A Notice of Assessment is the notice that tells you the county’s value and basic assessment information for your property. In Boulder County, the official notice name is Notice of Valuation (NOV). Boulder County says the Assessor sends a Notice of Valuation to property owners around May 1, and that it describes the property, gives the actual value, and is used in submitting an appeal to the Assessor (Boulder County Assessor appeals).

Read the NOV line by line. Look for the value, classification, property description, and any listed characteristics that affect value. If the notice or property record says your home has more finished area than it really has, a finished basement that is not finished, or improvements that are wrong, your filing should explain that clearly.

If you appeal and the Assessor responds, the response is called a Notice of Determination (NOD). Boulder County’s glossary explains that the NOD is the Assessor’s determination on an appeal and gives the owner the opportunity to continue to the CBOE, also commonly referred to locally as the BOE (Boulder County NOD glossary).

What evidence helps

For “Property Value is too high,” the best evidence is usually qualified, arm’s-length sales of similar homes. Look for homes in the same location or market area, with similar property type, size, age, condition, quality, design, and land size.

For 2027, focus first on sales from July 1, 2024 through June 30, 2026. Sales after June 30, 2026 should not be used for the 2027 reappraised value. If there are too few qualified sales in that period, older sales may be considered only as a fallback under Colorado assessment practice, in preceding six-month increments and within the data-gathering limit.

Boulder County does not publish a hard mileage radius or fixed square-footage variance rule for homeowner-submitted comparable sales. TaxSauce uses a conservative screen to help narrow the search, but the controlling idea is similarity. A nearby sale is not automatically a good comparable if it is much larger, newer, differently finished, or in a different market setting.

Your evidence packet should include your requested value, a short explanation, comparable sale addresses, sale dates, sale prices, and supporting documents. Boulder County’s appeal materials tell taxpayers to provide evidence that the value is incorrect by including comparable sales, and the county’s valuation page explains that residential properties are valued by the market approach (Boulder County Assessor appeals, Boulder County valuation process).

For “Property Record is Incorrect,” attach documents that prove the correction. Photos can help show condition. A sketch, appraisal, building record, or contractor statement may help show square footage or unfinished space. Keep the explanation short and direct.

What the board can and cannot decide

The Assessor’s Office reviews value and classification. If you disagree with the Assessor’s Notice of Determination after a timely protest, you may file a written appeal to the Board of Equalization (BOE) by the BOE deadline. Boulder County states that the deadline to appeal the Assessor’s determination is September 15 (Boulder County Assessor appeals).

The BOE can hear disagreements with the Assessor’s valuation decision. Boulder County also warns that the value may be raised for any property appealed to the BOE if the Assessor’s representative asks for an increase and presents supporting information (Boulder County Board of Equalization).

The Assessor and BOE do not decide whether your taxes are too high as a general complaint. Boulder County says taxes cannot be appealed through the Assessor’s Office. Tax bills are affected by assessment rates, mill levies, and budgets set by local taxing entities such as schools, cities, towns, and special districts (Boulder County Assessor appeals, Boulder County tax calculation).

How TaxSauce helps

TaxSauce helps you make sense of the value question before you file. We can estimate whether the Assessor’s value appears high, organize qualified comparable sales, flag property-record issues, and prepare a clear evidence packet for your review.

You stay in control. You review the facts, choose the argument you want to make, and decide whether to submit. TaxSauce does not promise a reduction, does not guarantee a filing will be accepted, and does not replace Boulder County’s official instructions.

For Boulder County, we focus on the dates and terms that matter: the expected June 8, 2027 Assessor protest deadline, the June 30, 2026 valuation date, the July 1, 2024 through June 30, 2026 primary sales period, and the official reasons that match your situation.