How Colorado values your home and turns value into a tax bill
Protest Your Colorado Property Tax Value · 1 study hours
Bottom line: Your tax bill is actual value x assessment rate x mill levy, and only the actual value (based on sales in the data-gathering period) can be protested.
Bottom line first. Your property tax bill is three numbers multiplied together: the value the county assessor puts on your home, a percentage that turns that value into a smaller taxable number, and a tax rate set by the local governments that bill you. You can only protest the first one. Everything else in this course is about that first number.
Who decides the value
The county assessor is the elected county official who values every property in the county. The law says all real and personal property is appraised, and its actual value (the assessor's estimate of what the property is worth for tax purposes) is determined by the assessor of the county where it sits (C.R.S. 39-1-103(5)(a)).
For a home, the law says actual value of residential real property (land and the houses on it that people live in) is determined "solely by consideration of the market approach to appraisal" (C.R.S. 39-1-103(5)(a)). The market approach means the value is based on what similar properties actually sold for. That is good news for you: sales are facts you can look up and compare.
Step 1: actual value
This is the number printed on your notice. It is not a price you paid and not a bid anyone made. It is the assessor's opinion of value, based on sales from an earlier window of time (explained below).
Step 2: the assessment rate
The state does not tax the full actual value. It first multiplies actual value by an assessment rate, which is set by law and has changed several times since 2023. The result is the assessed value. A 2024 law (HB24B-1001 (2024), Colorado General Assembly) gave assessed value and "valuation for assessment" separate definitions, so do not treat the two terms as the same. The residential rate was lowered for the 2023 property tax year (SB23B-001 (2023), Colorado General Assembly), kept for 2024 (SB24-233 (2024), Colorado General Assembly), and changed again for 2025 and later (HB24B-1001 (2024)). Those rates depend on the year and on the type of levy, so do not use one number for everyone. Nonresidential rates are in C.R.S. 39-1-104. Since HB24B-1001, the notice no longer has to print the ratio, so ask your county assessor which rate applies to your property.
One rule matters a lot: a change in the assessment rate is not a reason to protest. The statute says any change of the ratio "shall not constitute grounds" for an objection (C.R.S. 39-5-122(2)).
Step 3: the mill levy
A taxing entity is a local government that bills property tax, such as a school district or a fire district. Each sets a mill levy: a rate where one mill means one dollar of tax for every $1,000 of assessed value. (This is general knowledge; the mill levy is set by the districts, not by the assessor, and you cannot protest it on your notice.) Your total rate is the sum of every district's mills that cover your address.
Example with real numbers
The rates below are made up for the arithmetic and are not the current rates. Use your own notice for the real ones.
- Jordan's notice says actual value is $500,000.
- Made-up assessment rate: 6.5%. $500,000 x 0.065 = $32,500 assessed value.
- Made-up total mill levy: 90 mills, which is $90 per $1,000 of assessed value, or 0.090. $32,500 x 0.090 = $2,925 tax for the year.
- Now say Jordan wins a protest and the value drops to $460,000. $460,000 x 0.065 = $29,900. $29,900 x 0.090 = $2,691.
- Savings: $2,925 - $2,691 = $234 per year. Every $1,000 cut from actual value saves $1,000 x 0.065 x 0.090 = $5.85 a year at these made-up rates.
Bottom line of the example: a lower actual value flows straight through to a lower bill, in proportion.
The data-gathering period
The assessor does not value your home using today's market. The law sets a level of value: the actual value found from sales in a specific past window. As the statute text we checked reads, that window is the one-and-one-half-year period right before the July 1 that precedes the assessment date. If there are not enough sales for a type of property, the assessor may add earlier six-month periods, going back no more than five years before that July 1 (C.R.S. 39-1-104(10.2)(d)). This is called the data-gathering period, and values are adjusted to its final day (C.R.S. 39-1-104(10.2)(a)).
Why this matters: a comparable sale only helps your case if it happened inside that window. A sale from last month usually does not count for this year's value.
The reassessment cycle
A reassessment cycle is a block of time using the same level of value. The statute sets each cycle at two full calendar years (C.R.S. 39-1-104(10.2)(a)). In the first year the assessor revalues everything. In the second year, the assessor generally keeps the first year's value, as adjusted by protests and appeals, unless evidence says it must change (C.R.S. 39-1-103(15)).
The assessor may still change a value in the in-between year for "unusual conditions," such as an addition or remodel, damage from fire or a storm, or a change of use (C.R.S. 39-1-104(11)(b)(I)). Your first-year notice must also list the characteristics of your land and buildings that drive value (C.R.S. 39-5-121(1)(b)(I)).
What to remember
- Value x assessment rate x mill levy = tax.
- You can protest the value, not the rate, not the mill levy, not the tax estimate.
- Only sales in the data-gathering period count toward the level of value.
- Two-year cycle: the first year is the big revaluation.
This is general education, not legal or tax advice.
Law cited
- C.R.S. 39-1-103
- C.R.S. 39-1-104
- C.R.S. 39-5-121
- C.R.S. 39-5-122
- SB23B-001 (2023), Colorado General Assembly
- SB24-233 (2024), Colorado General Assembly
- HB24B-1001 (2024), Colorado General Assembly
Key terms
- Assessor
- The elected county official who values all property in the county.
- Actual value
- The assessor's estimate of what your property is worth for tax purposes; this is the number you can protest.
- Residential real property
- Land and buildings people live in; the law values it by the market approach only.
- Market approach
- Valuing a property by what similar properties actually sold for.
- Assessment rate
- The percentage set by law and multiplied by actual value to get assessed value. It changed for 2023 through 2025, so check your year.
- Assessed value
- Actual value times the assessment rate; the amount the tax rate is applied to. HB24B-1001 (2024) defines it separately from valuation for assessment.
- Taxing entity
- A local government, such as a school or fire district, that bills property tax.
- Mill levy
- A tax rate set by each taxing entity; one mill is $1 of tax per $1,000 of assessed value.
- Level of value
- The actual value found from sales in a set past window of time.
- Data-gathering period
- The past window of sales the assessor must use; the statute text we checked starts with the 18 months before the July 1 that precedes the assessment date.
- Reassessment cycle
- A two-year block that uses the same level of value; the first year is the full revaluation.
Flashcards
What three numbers multiply to make a property tax bill?
Actual value, assessment rate, and mill levy (with assessed value in the middle).
What is actual value?
The assessor's estimate of your property's worth for tax purposes; the number on your notice.
What approach sets a home's value?
The market approach alone: what similar properties sold for (C.R.S. 39-1-103(5)(a)).
What is assessed value?
Actual value multiplied by the assessment rate. HB24B-1001 (2024) defines it separately from valuation for assessment.
What is one mill?
One dollar of tax per $1,000 of assessed value.
Can you protest a change in the assessment rate?
No. A change of the ratio is not grounds for a protest (C.R.S. 39-5-122(2)).
What is the data-gathering period?
The past window of sales used for the level of value; it starts with the 18 months before the July 1 that precedes the assessment date.
How long is a reassessment cycle?
Two full calendar years (C.R.S. 39-1-104(10.2)(a)).
Can a value change in the second year of a cycle?
Yes, for unusual conditions such as an addition, remodel, or damage (C.R.S. 39-1-104(11)(b)(I)).
At made-up rates of 6.5% and 90 mills, what does each $1,000 of actual value cost per year?
$1,000 x 0.065 x 0.090 = $5.85.
Quiz: 10 questions
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Who determines the actual value of a home for property tax purposes?
- A The state treasurer
- B The assessor of the county where it sits
- C The school district that bills you
- D The title company that closed your purchase
Show answer and why
Answer: B. The assessor of the county where it sits
The statute gives the appraisal and actual-value decision to the county assessor. Districts only set their tax rates after values are known.
C.R.S. 39-1-103(5)(a)
Which method alone is used to determine a home's actual value?
- A The cost approach alone
- B The income approach alone
- C Whatever the owner paid for it
- D The market approach
Show answer and why
Answer: D. The market approach
The statute says residential value is set "solely" by the market approach. The cost and income approaches are for other property types, and your own price is only one sale in the data.
C.R.S. 39-1-103(5)(a)
Which of these can you NOT protest on your notice of valuation?
- A A change in the assessment rate
- B An actual value you think is too high
- C A property you think was valued twice
- D A property you think was erroneously assessed to you
Show answer and why
Answer: A. A change in the assessment rate
The statute lists too-high value, double valuation, exemption and erroneous assessment as protest reasons, and says a change of ratio is not grounds. The ratio is set by law, not by the assessor's opinion.
C.R.S. 39-5-122(2)
Using made-up numbers: actual value $400,000, rate 7%, 80 mills. What is the tax?
- A $2,800
- B $22,400
- C $2,240
- D $1,960
Show answer and why
Answer: C. $2,240
$400,000 x 0.07 = $28,000 assessed value; $28,000 x 0.080 = $2,240. $2,800 uses 100 mills by mistake, and $22,400 misplaces a decimal.
C.R.S. 39-1-104(3)
What does a reassessment cycle consist of, under the statute text we checked?
- A One calendar year
- B Two full calendar years
- C Three calendar years
- D Five calendar years
Show answer and why
Answer: B. Two full calendar years
The statute sets each cycle at two full calendar years. Five years shows up only as the farthest back an assessor may look for sales when sales are scarce.
C.R.S. 39-1-104(10.2)(a)
In the second year of a cycle, an assessor may change a home's value because of which of the following?
- A Neighbors saying the area feels pricier
- B A change in the school district's mill levy
- C A newspaper article about home prices
- D A bedroom addition built that year
Show answer and why
Answer: D. A bedroom addition built that year
Additions and remodels are named "unusual conditions" that can change value between level-of-value changes. A mill levy change affects the tax, not the value.
C.R.S. 39-1-104(11)(b)(I)
Using made-up rates (6.5% and 90 mills), how much does a $30,000 cut in actual value save per year?
- A $1,755.00
- B $195.00
- C $175.50
- D $30.00
Show answer and why
Answer: C. $175.50
$30,000 x 0.065 = $1,950 assessed; $1,950 x 0.090 = $175.50. $195.00 uses 0.1 instead of 0.090 in the mill step, and $1,755 is ten times too high.
C.R.S. 39-1-104(3)
Why is a sale from last month usually not helpful to prove this year's value?
- A It falls after the data-gathering period
- B Sales must be at least 10 years old
- C Only sales between family count
- D The assessor cannot read recent sales
Show answer and why
Answer: A. It falls after the data-gathering period
Values rest on sales in the data-gathering period before the July 1 that precedes the assessment date, adjusted to its end. Age is not the problem; timing is.
C.R.S. 39-1-104(10.2)(d)
What is a mill?
- A One percent of actual value
- B One dollar of tax per $1,000 of actual value
- C One thousandth of your income
- D One dollar of tax per $1,000 of assessed value
Show answer and why
Answer: D. One dollar of tax per $1,000 of assessed value
Mills apply to assessed value, not actual value. The distinction is why the assessment rate step matters.
C.R.S. 39-1-104(3)
What does a first-year notice of valuation include that helps you check your home's facts?
- A A list of every neighbor's sale price
- B An itemized listing of land and improvements and their value-related characteristics
- C The assessor's appraiser notes in full
- D A copy of your deed
Show answer and why
Answer: B. An itemized listing of land and improvements and their value-related characteristics
The statute requires the first notice of each reassessment cycle to list the land and improvements and the characteristics germane to value. Neighbor prices and notes are not part of the notice.
C.R.S. 39-5-121(1)(b)(I)