The basic formula: assessed value × mill rate ÷ 1,000

To calculate property tax using mill rate, you need two numbers: your property's assessed value (what your local assessor says it is worth for tax purposes) and the mill rate (the tax rate your county or municipality sets). Multiply the assessed value by the mill rate, then divide by 1,000. The result is your annual property tax bill.

The division by 1,000 exists because a mill rate is expressed per $1,000 of assessed value. If your assessed value is $300,000 and your mill rate is 15 mills, the math is: ($300,000 × 15) ÷ 1,000 = $4,500 in property tax.

This formula is the same across all states that use mill rates, though the assessed value itself — and how it is calculated — varies by location. Some assessors use market value; others use a percentage of market value. That variation matters more to your final bill than the formula does.

Key Takeaways

  • Mill rate is the tax rate per $1,000 of assessed value, so you divide your result by 1,000 after multiplying assessed value by the mill rate.
  • Your assessed value comes from your county or municipal assessor's office, not from what you paid for the property or what it would sell for today.
  • Mill rates are set by your local government and change year to year; you can find the current rate on your assessor's website or tax bill.
  • Some states assess property at full market value; others at a fraction of it, which directly affects how high your mill rate needs to be to raise the same revenue.

Where to find your assessed value

Your assessed value appears on your property tax bill, usually near the top. If you do not have a recent bill, contact your county assessor's office directly — they maintain a public record of every property in the county and can tell you the assessed value over the phone or online.

Many counties now publish assessments online through a searchable database. Search "[your county] assessor" or "[your county] property appraiser" to find the portal. You will need your address or parcel number. The assessed value shown is the one to use in your calculation, not the price you paid or the current market estimate.

If you believe your assessed value is wrong — too high compared to similar properties or to recent sales — you can file an appeal with your assessor. That is a separate process, but it directly affects your tax bill if successful.

Where to find the mill rate

Your mill rate is set by your county, city, or school district (or a combination of all three). The rate appears on your property tax bill, usually labeled as "mill rate," "tax rate," or "millage rate." It is also posted on your assessor's website and on the county treasurer's or tax collector's website.

Mill rates change every year as local governments adjust their budgets. If you are calculating tax for the current year, use the current mill rate. If you are estimating for next year, you can use the current rate as a rough guide, but the actual rate will not be final until the local government adopts its budget — usually in late summer or early fall.

Some properties have multiple mill rates stacked on top of each other: one for the county, one for the city, one for schools, and sometimes one for a special district (fire, water, library). Your bill shows the combined rate, or you can add the individual rates together to get the total.

How assessed value differs from market value

Your assessed value is not the same as what your house would sell for. Assessors use sales data, comparable properties, and formulas to estimate value, but they are not appraising your home the way a bank would before a mortgage. The assessed value is a tax value, and it is often lower than market value — sometimes significantly.

Some states assess property at 100 percent of market value. Others assess at 50 percent, 33 percent, or some other fraction. This fraction is called the assessment ratio. If your state assesses at 50 percent and your home would sell for $400,000, the assessed value might be $200,000. The mill rate is then set high enough to raise the needed revenue from that lower base.

You cannot change your assessed value by arguing that the market value is different. You can appeal if you believe the assessed value is wrong — meaning the assessor made an error in their calculation or used outdated data — but that is different from disagreeing with the assessment ratio itself.

Worked example with real numbers

Suppose you own a home in a county where the assessed value is $250,000 and the combined mill rate (county, city, and schools) is 18 mills. Here is the calculation:

$250,000 × 18 ÷ 1,000 = $4,500

Your annual property tax bill is $4,500. If your county bills quarterly, you would pay $1,125 four times a year. If it bills semi-annually, you would pay $2,250 twice a year. The total is the same; only the payment schedule changes.

Now suppose the mill rate increases to 19 mills the following year (because the county raised its budget). Your new bill would be $250,000 × 19 ÷ 1,000 = $4,750. That is a $250 increase, or about 5.6 percent. If your assessed value also increased — say, to $260,000 — and the mill rate stayed at 18, your bill would be $260,000 × 18 ÷ 1,000 = $4,680, an increase of $180.

What happens if your assessed value changes

Assessors reassess properties on a schedule set by state law. Some counties reassess every year; others every three to five years. When your property is reassessed, the assessed value may go up, down, or stay the same. Your tax bill changes accordingly, even if the mill rate does not.

You will receive a notice of the new assessed value before it takes effect, usually 30 to 60 days before the new tax year. This notice tells you the new value and how to appeal if you disagree. If you do not appeal within the important date — typically 30 days — the new value becomes final.

Some states have homestead exemptions or assessment caps that limit how much your assessed value can increase in a single year, even if the market value rises sharply. Florida, for example, caps increases at 3 percent per year for homesteaded properties. Check your state or county rules to see if you may have access to for any such protection.

Using the mill rate to estimate future tax bills

If you know your current assessed value and mill rate, you can estimate next year's bill by assuming the mill rate stays the same and the assessed value increases by a small percentage — typically 2 to 5 percent, depending on your area and recent trends.

For example, if your current bill is $4,500 and you expect a 3 percent increase in assessed value with no change in mill rate, estimate $4,500 × 1.03 = $4,635. This is a rough guide only. The actual bill depends on what the assessor does and what the local government decides about the mill rate.

For a more precise estimate, contact your assessor and ask whether a reassessment is scheduled for your property in the coming year. If one is, ask for the preliminary assessed value. If not, you can assume the assessed value will stay the same unless your property has been significantly improved or damaged.

Frequently Asked Questions

Why is it called a mill rate?

A mill is one-tenth of a cent, or $0.001. A mill rate of 15 mills means $0.015 per dollar of assessed value, or $15 per $1,000. The term is historical and refers to the way tax rates were originally expressed. You do not need to think in mills; just remember to divide by 1,000 after multiplying.

Can I reduce my property tax by lowering my assessed value?

You cannot lower your assessed value just by asking. You can file an appeal if you believe the assessor made an error — for example, if they overestimated the size of your home or did not account for damage. You will need evidence, such as a recent appraisal, comparable sales, or photos of the condition of the property.

What if my property is in two different tax districts?

If your property straddles a county or city line, it may be subject to two different mill rates. The assessor's office will split the assessed value between the two districts and calculate tax for each separately. Your bill will show both amounts. This is rare but does happen in some areas.

Does the mill rate include school taxes?

Usually yes. The mill rate on your bill is typically a combined rate that includes county, city, and school district taxes. Your bill may break it down by component, or it may show only the total. If you want to know how much of your bill goes to schools, contact your assessor or school district.

How often do mill rates change?

Mill rates change every year as local governments adopt new budgets. The change is usually small — 1 to 3 percent — but it can be larger if the government faces a budget shortfall or decides to fund a new project. You will see the new rate on your tax bill each year.