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Property Tax Calculation

How Property Taxes Are Calculated

Actual Value, Assessment Rate, and Mill Levy

Assessment Rate

The Current Assessment Rate below reflects rates for the 2023 tax year that will impact tax bills paid in 2024.

Type of Property 2022 Assessment Rate 2023 Assessment Rate 2023 Value Adjustment


Multi-Family housing
Duplex/Triplex, 4-8 unit Apartments, 9+Unit Apartments
6.8% 6.7% -$55,000
All other residential property
Single family, Condominiums, Townhomes
6.95% 6.7% -$55,000


Hotel, motels and B&B 29% 27.9% -$30,000
Renewable Energy 26.4% 26.4% -$30,000
Agricultural 26.4% 26.4%
Vacant Land 29% 27.9%
Commercial 29% 27.9% -$30,000
Industrial 29% 27.9%
Oil & Gas production 87.5% 87.5%

Property Tax Calculation

Property taxes are calculated using the actual property value, the assessment rate, and the mill levy using the formula: Actual Value x Assessment Rate = Assessed Value x Mill Levy = Taxes Due.

For tax year 2023 (taxes paid in 2024), there is an additional component for some properties. In 2022, the Colorado Legislature passed SB22-238 which reduces assessment rates and also provides a one time value adjustment to residential ($15,000 adjustment) and commercial ($30,000 adjustment) for tax year 2023.

In November 2023, the Colorado Legislature held a special session and passed SB23B-001. This bill increased the residential reduction from $15,000 to $55,000 and lowered the residential assessment rate from 6.765% to 6.7%. The original reductions for commercial properties from SB22-238 remain. Properties that fall into these categories will have the value adjustment applied to their Actual Value before multiplying by the assessment rate. For example:

( Actual
) X Assessment
= Assessed

& then

X Mill
= Taxes

For a residential property with an Actual Value of $450,000 with a Value Adjustment of $55,000, an Assessment Rate of 6.7%, and a Mill Levy of 92, there will be $2,435 in taxes due.


(or 0.067)


& then

(or 92 Mills
or 0.092)


Additional details on the Assessment Rate and Mill Levy are below. Seniors and disabled veterans may qualify for certain property tax exemptions.

Much more information on property taxes, including Property Tax Search, due dates, and paying taxes online, is available on the Boulder County Treasurer page.

Tax Rate or Mill Levy

The Tax Rate and Mill Levy are two different ways of expressing the same information. The Tax Rate is expressed as a percentage, while the Mill Levy is expressed in mills (1 mill = $1 of property tax for every $1,000 of assessed value)

Generally, properties are affected by several taxing entities. Each taxing entity determines what revenues will be required to operate during the coming fiscal year. The required revenues are then divided by the total assessed value to determine the tax rate/mill levy for each entity. To determine the total tax rate for a property, add the tax rates for each entity that impacts a property.

Mill Levy Example:

  • The assessor determines the total assessed value for properties within a school district’s boundaries as $100,000,000.
  • The school board of that school district determines the budgeted property tax revenues needed are $1,398,000.
  • $1,398,000 (tax revenue) divided by $100,000,000 (assessed value) = 1.3980% Tax Rate, or 13.98 Mills (Mill Levy), for that district’s portion of the total Mill Levy.
  • The school district’s tax rate is $13.98 in revenue needed for each $1,000 of assessed value.

Contact Us


Phone: 303-441-3530
Fax: 303-441-4996


Mailing Address

PO Box 471
Boulder, CO 80306-0471

Hours: 7:30 a.m. to 5 p.m.
Closed Friday


Assessor Boulder and Longmont Drop Boxes


1325 Pearl St., 2nd floor
Boulder, CO 80302
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Map and Directions Boulder Location


515 Coffman St., Suite 114
Hours: 7:30 a.m. to 5 p.m.
Monday only
Map and Directions Longmont Location


1755 S Public Road
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Tuesday only
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