The Basic Formula: Assessed Value × Millage Rate ÷ 1,000

Property tax is calculated by multiplying your property's assessed value by the millage rate, then dividing by 1,000. A millage rate is expressed in mills — each mill equals $1 of tax per $1,000 of assessed property value. So if your home is assessed at $300,000 and your millage rate is 15 mills, you multiply 300,000 by 15 and divide by 1,000 to get $4,500 in annual property tax.

The millage rate is set by your local government — usually your county assessor's office or a city tax authority — and it changes year to year based on the budget needs of schools, fire departments, and other public services in your area. Your assessed value is determined by your assessor's office and is typically a percentage of your property's market value, though that percentage varies by state.

You do not need to calculate this yourself for your tax bill — your assessor's office does it and sends you the result. But understanding the calculation helps you see where your tax bill comes from and why it changes from year to year.

Key Takeaways

  • The formula is assessed value multiplied by millage rate, divided by 1,000, and your assessor's office performs this calculation for you.
  • Millage rates are set by local government and expressed in mills, where one mill equals $1 of tax per $1,000 of assessed value.
  • Your assessed value is usually a fraction of your home's market value, and that fraction (called the assessment ratio) varies by state.
  • You can find your assessed value and millage rate on your property tax bill, your assessor's website, or by contacting your county assessor directly.
  • Changes in your tax bill year to year come from changes in either the assessed value or the millage rate, or both.

Where to Find Your Assessed Value

Your assessed value appears on your annual property tax bill, usually near the top or in a section labeled "property information" or "assessment details." If you have lost your bill or want to check the value before the bill arrives, you can look it up online through your county assessor's website — most counties now post assessment records publicly.

To find your assessor's website, search "[your county name] assessor" or "[your county name] property appraiser." Once there, look for a link like "search property records," "look up assessment," or "property search." You will typically enter your address or parcel number, and the site will show your assessed value, your property description, and sometimes the millage rates that explore to your property.

If you cannot find it online, call your county assessor's office directly. They can tell you your assessed value over the phone and explain how it was calculated. This is a public record, so there is no fee to request it.

Understanding Millage Rates in Your Area

A millage rate is a tax rate expressed per $1,000 of assessed value. If your millage rate is 20 mills, that means you pay $20 in tax for every $1,000 your property is assessed at. Millage rates are not the same everywhere — they vary by county, city, school district, and sometimes by neighborhood, because different areas have different funding needs and different numbers of properties to spread the cost across.

Your property tax bill usually lists all the millage rates that explore to your address. You might see one rate for the county, another for the city, another for the school district, and possibly others for fire protection, library services, or special districts. Each rate is applied separately to your assessed value, and the results are added together to get your total tax bill.

Millage rates change every year. Your assessor's office publishes the new rates before the tax year begins, and they appear on your bill. If you want to see the rates before your bill arrives, check your assessor's website or call the office.

How Assessment Ratios Affect Your Calculation

In many states, the assessed value is not the full market value of your home — it is a percentage of it. That percentage is called the assessment ratio, and it varies by state. Some states assess at 100 percent of market value; others assess at 50 percent, 33 percent, or another figure. A few states use different ratios for different property types.

This matters because it affects how your tax bill compares to your neighbor's, even if your homes are worth the same. If your state assesses at 50 percent and your home's market value is $400,000, your assessed value is $200,000. If another state assesses at 100 percent and a home there is worth $400,000, its assessed value is $400,000 — and its tax bill will be higher even if the millage rate is lower.

You can find your state's assessment ratio on your assessor's website or by calling the office. It is usually the same statewide, though some states allow counties to set their own.

Why Your Tax Bill Changes Year to Year

Your property tax bill can change for two reasons: your assessed value changed, or the millage rate changed, or both. If your home was renovated, expanded, or significantly damaged, your assessed value may increase or decrease. If your county or school district raised its budget, the millage rate may go up. If property values in your area fell, your assessed value might drop.

Most assessors reassess all properties in their jurisdiction every year, though the frequency varies by state — some reassess every three years or every five years. When you receive your tax bill, it will show the assessed value used to calculate it. If you think the value is wrong, you have the right to appeal it; your bill or assessor's website will explain the appeal process and the important date.

Millage rates are set by elected officials and published before the tax year begins. If you want to know why the rate changed, you can attend a county commission meeting or school board meeting where the budget is discussed, or you can call your assessor's office and ask.

Worked Example: Putting the Formula to Use

Suppose your property is assessed at $250,000 and your area has a combined millage rate of 18 mills (which might be 8 mills for the county, 7 mills for schools, and 3 mills for the city). The calculation is:

$250,000 × 18 ÷ 1,000 = $4,500

Your annual property tax is $4,500. If you pay in monthly installments, that is roughly $375 per month. If next year your assessed value stays the same but the millage rate rises to 19 mills, your tax becomes $250,000 × 19 ÷ 1,000 = $4,750 — a $250 increase. If the millage rate stays at 18 mills but your assessed value rises to $260,000 (because you added a deck or your home's market value increased), your tax becomes $260,000 × 18 ÷ 1,000 = $4,680 — a $180 increase.

When to Contact Your Assessor

Contact your assessor if you believe your assessed value is wrong — for example, if it lists your home as having four bedrooms when it has three, or if it does not account for a major repair or loss. You have the right to appeal your assessment, and the important date is usually 30 to 60 days after you receive your bill, though this varies by state. Your bill or assessor's website will state the important date and the process.

You should also contact your assessor if you made a major home improvement and want to understand how it might affect your assessed value in future years. Some improvements increase assessed value; others do not. Knowing this ahead of time can help you plan.

If you cannot find your assessed value or millage rate, or if you do not understand your bill, call your county assessor's office. They are accustomed to these questions and can walk you through the numbers.

Frequently Asked Questions

What is the difference between assessed value and market value?

Market value is what your home would sell for today. Assessed value is the value your assessor assigns for tax purposes, which is often lower than market value. In many states, assessed value is a set percentage of market value — for example, 50 percent. Your tax bill is based on assessed value, not market value.

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

You cannot lower your assessed value yourself, but you can appeal it if you believe it is wrong. If you have evidence that your home is worth less than the assessed value — such as a recent appraisal or comparable sales in your area — you can file an appeal with your assessor's office. The process and important date vary by state.

Does the millage rate include school taxes?

Yes, in most places. School taxes are usually one component of the total millage rate. Your tax bill will break down how much of your total tax goes to the school district, the county, the city, and any other local services. You can see these rates listed separately on your bill.

What happens if I disagree with my millage rate?

Millage rates are set by elected officials — county commissioners, city councils, and school boards — based on their budgets. If you disagree with the rate, you can attend a public meeting where the budget is discussed, speak during public comment, or contact your elected representatives. You cannot appeal the millage rate itself the way you can appeal your assessed value.

How often do assessed values change?

Most assessors reassess properties annually, though some states reassess every three or five years. Even in states with annual reassessment, your assessed value may not change every year — it changes only if the assessor finds a reason to adjust it, such as a home improvement, damage, or a significant shift in local property values.