What Is a Mill Rate? How Millage Rates Determine Your Property Tax Bill

When you receive a property tax bill, the rate is often listed in mills — a unit of measurement that confuses many homeowners. "What does 18.5 mills mean? How does that become an actual dollar amount?" These are entirely reasonable questions. Mill rates are simply one way of expressing a tax rate, and the math is straightforward once you know the definition.

Definition: What Is One Mill?

One mill equals $1 of tax for every $1,000 of taxable assessed value. The word "mill" comes from the Latin "mille," meaning one thousand. It is the same root as "millennium" (one thousand years) and "millimeter" (one thousandth of a meter).

To express a mill rate as a decimal, simply divide by 1,000. A mill rate of 18 is equivalent to 0.018, or 1.8%. A mill rate of 25 is 0.025, or 2.5%.

The formula for calculating your property tax from a mill rate is: Tax = (Taxable Assessed Value ÷ 1,000) × Mill Rate.

A Worked Example

Suppose your home has a taxable assessed value of $300,000 and your jurisdiction's total mill rate is 18. Your annual property tax bill would be calculated as follows:

$300,000 ÷ 1,000 = 300. 300 × 18 = $5,400. You owe $5,400 per year in property taxes.

Now suppose the school district passes a bond measure that adds 2.5 mills to the rate, bringing the total to 20.5 mills. Your new bill is: 300 × 20.5 = $6,150. The 2.5-mill addition costs you $750 more per year.

This is exactly how tax bill changes are communicated in local government: "The school district is requesting an increase of 1.8 mills." Now you can calculate what that means for your specific property.

Who Sets the Mill Rate?

Each taxing jurisdiction — county, school district, city, fire district, library district, etc. — sets its own mill rate independently. The mill rate is not simply chosen arbitrarily. It is derived from the levy and the tax base.

Each year, a taxing entity's governing body (school board, county commissioners, city council) approves a total budget and determines how much of that budget will be funded by property taxes — this is the levy. The levy is then divided by the total equalized assessed value of all taxable property in the jurisdiction (the tax base). The result is the mill rate.

Formula: Mill Rate = (Levy ÷ Tax Base) × 1,000.

If a school district needs $50 million and the total taxable value of all property in the district is $5 billion, the mill rate is: ($50,000,000 ÷ $5,000,000,000) × 1,000 = 10 mills. If the tax base grows (new construction, appreciation), the same levy produces a lower mill rate. If the tax base shrinks, the rate must rise to maintain the same revenue.

Why Mill Rates Vary So Much Between Jurisdictions

Mill rates vary enormously between neighboring jurisdictions — sometimes by a factor of 2 or 3 — even when the underlying services are similar. The explanation lies in the formula above: the mill rate is the levy divided by the tax base.

A jurisdiction with a large, high-value tax base — affluent suburbs, dense commercial corridors, or areas with significant industrial property — can fund comparable services at a lower mill rate because each mill generates more revenue. A rural or lower-income jurisdiction with a small or low-value tax base must levy a much higher rate to raise the same dollar amount.

This is why you frequently see the paradox of high mill rates in lower-income areas with modest home values, and low mill rates in affluent communities with high home values. The affluent community can afford excellent services at 12 mills; the less wealthy community struggles to fund basic services at 25 mills.

State equalization aid and grant programs attempt to compensate for this disparity — particularly for school funding — but the property tax base still determines local fiscal capacity in most states.

Mill Rate vs. Effective Tax Rate

A mill rate applies to assessed value, which may be a fraction of market value depending on your state's assessment practices. The effective tax rate is the tax paid as a percentage of market value — and it is the more useful metric for comparing tax burdens across jurisdictions with different assessment ratios.

Example: Two homes, each worth $400,000 on the market. In Jurisdiction A, property is assessed at full market value and the mill rate is 15. Tax = (400,000 ÷ 1,000) × 15 = $6,000. Effective rate = $6,000 ÷ $400,000 = 1.5%.

In Jurisdiction B, property is assessed at 33% of market value, giving an assessed value of $133,000. The mill rate is 30. Tax = (133,000 ÷ 1,000) × 30 = $3,990. Effective rate = $3,990 ÷ $400,000 = approximately 1.0%.

Despite Jurisdiction B having double the mill rate, homeowners pay less in effective terms because of the lower assessment ratio. This is why PropertyTaxByZip shows effective tax rates — taxes as a percentage of home value — rather than mill rates, which cannot be compared across jurisdictions without knowing the assessment ratio.

Data Source

ZIP-level property tax data on PropertyTaxByZip comes from the U.S. Census Bureau, American Community Survey 2019-2023 5-Year Estimates. Mill rate and assessment ratio information is provided for educational purposes. Actual mill rates for a specific property must be obtained from your local county assessor or tax collector.