Boulder County Property Tax: Rates & Appeals (2026)

If you already filed a 2026 real-property appeal with the Boulder County Assessor and disagree with the Notice of Determination, your next deadline is September 15, 2026 to appeal to the Boulder County Board of Equalization (BOE) at www.boco.org/BOE. If you did not file the first-level Assessor appeal by June 8, 2026, the regular 2026 residential valuation appeal window is closed.

For the first-level appeal, Boulder County used the 2026 Real Property Appeal Form and accepted filings online at boco.org/AssessorAppeals, by email, mail, fax, drop box, or in person at the Assessor’s Office.

How assessments work in Boulder County

Boulder County is on Colorado’s two-year reappraisal cycle. The Assessor revalues real property in odd-numbered years, and 2026 is an intervening year: if your property’s condition and classification did not change, your value generally carries forward from 2025. For tax year 2026, Boulder County values the home as it existed on January 1, 2026, but estimates what it would have sold for on the statutory appraisal date, June 30, 2024.

That date matters. A sale in late 2025 may help you understand the market, but Boulder County’s 2025/2026 residential value is built from sales in the base period ending June 30, 2024. The county says it uses a 24-month sales period, July 1, 2022 through June 30, 2024, and may look farther back only if there are not enough sales. Residential property is valued by the market approach, using comparable sales and mass appraisal rather than a full interior appraisal for every home.

The tax bill is separate from the value appeal. Beginning with 2025 taxes paid in 2026, Boulder County residential bills use split residential assessed values: 7.05% for school districts and 6.25% for local governments in tax year 2025; for tax year 2026 paid in 2027, the county’s table shows 7.05% for school districts and 6.8% for local governments, with a local-government value reduction of 10% of the first $700,000 in actual value.

Your mill levy depends on your tax area, school district, city/town, fire district, library district, and special districts. Boulder County’s own 2025-payable-2026 example uses a school levy of 30 mills and local-government levies totaling 65 mills. The county’s 2025 countywide net Boulder County levy, by resolution, is 24.046 mills, but that is only the county portion, not your whole tax bill.

Whether you should appeal

Appeal if you can show the Assessor’s actual value or classification is wrong. Boulder County specifically points homeowners to errors such as wrong square footage, bedroom/bath count, finished basement status, lot size, condition, or improvements, plus comparable sales that support a different June 30, 2024 value. Do not appeal just because the tax bill feels high; the Assessor and BOE do not change city, school, fire, or special-district budgets.

Start with three checks:

1. Read your Notice of Valuation or tax notice. Confirm the account number, current actual value, property class, and characteristics.
2. Use Boulder County’s comparable-sales tools. Look for similar homes in your market area that sold in the July 1, 2022–June 30, 2024 period.
3. Choose a specific value. Boulder County’s BOE petition requires a specific dollar estimate for real-property appeals.

A realistic savings example: suppose a Boulder County home is valued at $900,000, and the owner proves the correct value is $850,000, a $50,000 reduction. Using Boulder County’s 2025-payable-2026 residential rates and its example levies, the school portion savings is $50,000 × 7.05% × 30 mills = $105.75. The local-government portion is $50,000 × 6.25% × 65 mills = $203.13. Estimated annual savings: about $309. Your actual savings can be higher or lower depending on your tax area’s levies and whether the tax year uses the 2026 local-government value reduction.

Boulder County and Colorado publish forms, deadlines, and procedures, but I did not find an official county/state-published 2026 residential appeal success rate or median reduction. Treat any private-company “win rate” as marketing unless it is tied to public records.

Step-by-step how to file

First-level Assessor appeal — 2026 window closed. Boulder County accepted 2026 real-property appeals May 1 through June 8, 2026. Mailed appeals had to be postmarked by June 8; in-person filings were accepted through 5 p.m.; online and faxed appeals had to be timestamped by 11:59 p.m. The official form was the 2026 Real Property Appeal Form.

Filing methods listed by the county:

• Online: boco.org/AssessorAppeals
• Email: assessor@bouldercounty.gov
• Mail: Boulder County Assessor, P.O. Box 471, Boulder, CO 80306-0471
• Fax: 303-441-4996
• In person: 1325 Pearl St., 2nd Floor, Boulder, CO 80302, Monday–Thursday, 7:30 a.m.–5 p.m.
• Drop boxes: Boulder, Longmont, and Lafayette locations listed by the Assessor

The county does not list a filing fee for the Assessor appeal.

Second-level BOE appeal — deadline September 15, 2026. You may go to the BOE only if you appealed to the Assessor and received a Notice of Determination. File at www.boco.org/BOE; the county recommends the online system, and agents must use it with a signed Letter of Agency. Online BOE petitions must be submitted by 11:59 p.m. on September 15.

If you are an owner representing yourself, you may also use the Board of Equalization Appeal Petition form included with the Notice of Determination. Paper petitions may be mailed to Board of Equalization, P.O. Box 471, Boulder, CO 80306 and must be clearly postmarked by September 15. Hand delivery is to 1325 Pearl St., 1st Floor, Boulder, Monday–Thursday, 9 a.m.–4 p.m.; the hand-delivery deadline is 4 p.m. September 15. BOE does not accept faxed or emailed petitions. The BOE FAQ says there is no out-of-pocket cost to have a BOE hearing, although your own appraisal, evidence, or representative costs are yours.

What happens after

For on-time first-level appeals, the Assessor mails a Notice of Determination by August 15. If you move on to BOE, expect a fast process: hearings are generally in September and October and are held by Microsoft Teams video or phone, not in person.

BOE evidence is not automatically carried over from your Assessor appeal. Upload PDF evidence in the BOE system at least three business days before the hearing; Boulder limits uploads to five documents, and evidence cannot be emailed or introduced for the first time at the hearing.

At the BOE hearing, a hearing officer gives the oath, the Assessor’s representative speaks first, then you present your case. Boulder’s FAQ says hearings are 15 minutes, the hearing officer may ask questions, and you do not receive a decision at the hearing. The Boulder County Commissioners sit as the BOE, but hearing officers preside and make recommendations.

The BOE must decide by or on November 1, and the Notice of Decision is emailed within five business days after the BOE decision. If you still disagree, Boulder lists three next options: Colorado Board of Assessment Appeals, Boulder County District Court, or binding arbitration. For arbitration, Boulder’s petition shows a $150 residential deposit and $500 for other cases/classification disputes.

Local tips

• Use Boulder County’s time-trended comparable sales, not just Zillow or a recent neighborhood listing. The relevant valuation date is June 30, 2024.
• Argue the property, not the payment. “My taxes are too high” loses; “the Assessor used 1,900 finished square feet, but county permit records and photos show 1,650” is useful.
• Check exemptions separately. The Senior Homestead exemption can exempt 50% of the first $200,000 of actual value, up to $100,000, for qualifying seniors; the 2026 application deadline has passed, and 2027 applications open after January 1, 2027. Boulder also flags veteran-with-disability and Gold Star spouse exemptions, Qualified Senior Primary Residence Classification, senior/active-duty deferral, and the Senior Tax Worker Program.
• Do not miss BOE evidence rules. Evidence submitted to the Assessor is not sent to BOE. Re-upload it.
• Use your tax area for savings estimates. Find it in Boulder County Property Search or on the Treasurer tax account; a reduction in value saves tax only in proportion to your actual assessment rate and mill levies.

Boulder County Property Tax Rate

Boulder County government only: 2026 fiscal-year net county mill levy is 24.046 mills ($24.046 per $1,000 of assessed value), after a -0.932 temporary credit and 0.333 abatement mill levy; total parcel tax rates also include school, city/town, fire, and other taxing districts and vary by property.

Source: https://assets.bouldercounty.gov/wp-content/uploads/2026/01/resolution-2025-059-levying-general-property-taxes.pdf

When Are Property Taxes Due in Boulder County?

Payment due dates for 2026: first half March 2, 2026; full payment April 30, 2026; second half June 15, 2026. Colorado allows Boulder County property taxes to be paid either in two equal installments or in full by the listed due dates. No discounts for early payment.

This is not the same as the assessment appeal deadline above. The appeal deadline is your window to contest your assessed value; the payment due date is when the resulting tax bill must be paid. Missing one does not affect the other, but missing either has real consequences — one forfeits your right to appeal for the year, the other can trigger penalties and interest.

Source: https://bouldercounty.gov/property-and-land/treasurer/taxes/due-dates/

Property Tax Exemptions in Boulder County

• Senior Property Tax Exemption — For tax year 2026 payable in 2027, seniors must have been born on or before Jan. 1, 1961, and must have owned and lived in the home as their primary residence continuously since before Jan. 1, 2016; surviving spouses of previously qualified seniors may apply to continue the exemption.. 50% of the first $200,000 in actual value of the primary residence is exempt, up to $100,000 in actual value; Colorado pays the property taxes on the exempted value. Yes; the exemption remains in effect until a disqualifying event occurs, but a new application is required after certain events such as transfer to a trust, LLC, or other legal entity. Apply by Tax year 2026 deadline has passed; Boulder County says 2027 applications begin after Jan. 1, 2027. Senior applications are accepted through July 15.. (Source: https://bouldercounty.gov/property-and-land/assessor/senior-exemption/)
• Qualified Senior Primary Residence Classification — Qualifying seniors, or surviving spouses of seniors, who previously qualified for and received the Senior Property Tax Exemption on or after Jan. 1, 2020, are no longer eligible for that exemption, and occupy the property as their primary residence as of Jan. 1.. For tax year 2026, $100,000 of actual value of a primary residence is not taxed, unless that would reduce assessed value below $1,000. Yes; this is a time-limited classification for tax year 2026 only, according to Boulder County. Apply by Tax year 2026 deadline has passed; on-time deadline was March 15, 2026, with late filing accepted March 16 through July 15, 2026.. (Source: https://bouldercounty.gov/property-and-land/assessor/senior-exemption/senior-primary-residence/)
• Property Tax Exemption for Veterans with a Disability — A U.S. military veteran with a 100% permanent service-connected disability who owned and occupied the home as their primary residence since Jan. 1 of the application year.. Boulder County states this exemption extends the existing senior property tax exemption; the senior exemption amount is 50% of the first $200,000 in actual value, up to $100,000 in actual value. Yes. Apply by Tax year 2026 deadline has passed; Boulder County says 2027 applications begin after Jan. 1, 2027.. (Source: https://bouldercounty.gov/property-and-land/assessor/veteran-exemption/)
• Surviving Spouse of a Veteran with a Disability Exemption — Surviving spouse of a qualifying veteran with a disability, subject to the application eligibility requirements.. Yes. Apply by July 1; tax year 2026 deadline has passed.. (Source: https://bouldercounty.gov/property-and-land/assessor/veteran-exemption/)
• Gold Star Spouse Exemption — Surviving spouse of a Gold Star Veteran who owned and occupied the home as their primary residence since Jan. 1 of the application year.. Yes. Apply by July 1; tax year 2026 deadline has passed.. (Source: https://bouldercounty.gov/property-and-land/assessor/veteran-exemption/)
• Senior Property Tax Deferral — Homeowners age 65 or older on or before Jan. 1 of the year they defer taxes, who own and live in the property, subject to mortgage/lien and trust requirements.. Allows deferral of either the whole amount of property taxes or half of the property taxes; interest applies and taxes are postponed until the property is sold or the estate is settled after death. Yes; Boulder County Treasurer collects applications and sends them to the State of Colorado for eligibility determination. Apply by Applications are accepted January through mid-March for taxes payable that year; the completed application must be returned by the date indicated on the form.. (Source: https://bouldercounty.gov/property-and-land/treasurer/taxes/senior/)

How to Look Up Your Property Record in Boulder County

You can look up your property's official record at https://maps.bouldercounty.org/boco/PropertySearch/. Boulder County’s official Property Search provides detailed property records including ownership, assessments, zoning, septic systems, and plats.