How Colorado Property Taxes Are Calculated: Actual Value, Assessment Rates, and Mill Levies Explained

Your Colorado property tax bill is the product of three numbers, and only one of them is realistically yours to challenge. Understand the formula and you'll understand both why your bill jumped and where your leverage is.

1. Actual value — the assessor's estimate of market value

"Actual value" is what the county assessor believes your home would sell for. For residential property, Colorado requires the market approach: a statistical analysis of comparable sales during an 18-month study period ending June 30 of the even year before reassessment. Values are set in odd-numbered years and generally hold for two years. This is the number on your Notice of Valuation — and the only number in the formula you can appeal.

2. Assessment rate — the slice that's taxable

You don't pay taxes on the full actual value. Colorado multiplies it by a residential assessment rate — historically 7.15%, and lowered several times since the Gallagher Amendment's repeal in 2020. Recent legislation also split the rate in two: one rate for school district taxes and a slightly lower one for all other local governments, along with a value exemption that shaves a fixed amount off your actual value first. The exact percentages have changed almost every year — the Colorado Division of Property Taxation publishes the current rates, and your county assessor applies them. (Curious how we got here? Read our breakdown of Colorado's property tax overhaul.)

3. Mill levy — your local tax rates, stacked

One mill is $1 of tax per $1,000 of assessed (not actual) value. Your total mill levy is the sum of every taxing district your home sits in: school district (usually the largest share), county, city, fire, water, library — and in newer developments, metro districts, which can add dramatically to the total. Front Range totals commonly run from the 70s to over 150 mills depending on where you live.

A worked example

Take a Denver home the assessor values at $700,000, with a ~6.7% assessment rate and a ~90-mill total levy:

Now suppose the home is actually worth $640,000 and the assessor over-shot. The same math lands at roughly $3,860 — about $360 every year back in the owner's pocket once a successful appeal corrects the value. That's the entire logic of appealing: the rate and the levy are set by law and by voters, but the value is just an estimate, and estimates can be wrong.

Why did my bill jump so much?

• Reassessment caught a hot market. Values reset every two years to a past sales window — after big run-ups, assessed values leap all at once.
• Your mill levy changed. New voter-approved bonds or metro-district debt raise the levy without your value moving.
• An exemption fell off, such as the senior homestead exemption (which covers 50% of the first $200,000 of value for qualifying owners 65+ who've lived in the home 10 years).

Where your leverage is

You can't vote down a mill levy by yourself and the assessment rate is statewide — but the actual value is appealable by right, every cycle. If your county's estimate is even a few percent high, that's real money compounding year after year. See what your home's numbers look like — we'll pull your county's actual records and tell you honestly whether an appeal is worth it.