The basic formula: assessed value times mill rate divided by 1,000
Property tax is calculated by taking your home's assessed value, multiplying it by the mill rate, then dividing by 1,000. The result is your annual property tax bill. A mill rate of 15 mills, for example, means you pay $15 in tax for every $1,000 of assessed home value.
The assessed value is not the price you paid or what your home would sell for today. It is a value set by your county or municipal assessor, usually based on recent sales of similar homes in your area. The mill rate is set by your local government and varies significantly by location — a home worth $300,000 in one county might generate a very different tax bill than the same home in another county, because mill rates differ.
Here is a concrete example: if your home is assessed at $250,000 and your mill rate is 12 mills, the calculation is ($250,000 × 12) ÷ 1,000 = $3,000 per year in property tax.
Key Takeaways
- The formula is: (assessed value × mill rate) ÷ 1,000 = annual property tax.
- Mill rate is set by your local government and is published in your county or city budget documents each year.
- Assessed value comes from your county assessor and may be lower than your home's market value.
- Your property tax bill may include additional levies beyond the base mill rate, such as school district or fire district taxes.
Where to find your assessed value and mill rate
Your assessed value appears on your property tax bill, which you receive from your county assessor or tax collector. If you do not have a recent bill, you can contact your county assessor's office directly — most now publish assessed values online through a searchable database. Search "[your county name] assessor" plus "property search" or "assessment database" to find the portal.
The mill rate is published by your local government, usually in the annual budget or tax rate resolution. Your county tax assessor's office can tell you the current mill rate over the phone, or you can find it on the county website under "tax rates" or "mill rates." Some counties break the rate into components — a base rate for general county services, plus separate rates for schools, fire districts, and other local services. You may need to add these together to get your total mill rate.
If you live in a state or county that uses a different tax structure — for instance, some places use a percentage rate instead of mills — your tax assessor can convert the rate to mills or show you the calculation in the format your jurisdiction uses.
Understanding assessed value versus market value
Your home's assessed value is almost always lower than what it would sell for on the open market. Assessors use sales data from comparable homes to set assessed values, but they do not reassess every property every year in most states. This means your assessed value may lag behind actual market changes by one to three years, depending on your state's reassessment cycle.
Some states cap how much the assessed value can increase in a single year, even if the market value rises sharply. California, for example, limits annual increases to 2 percent under Proposition 13. Other states reassess all properties every few years. The reassessment schedule varies by state and sometimes by county within a state, so check your assessor's office for your local cycle.
If you believe your assessed value is too high compared to recent sales of similar homes, you can file a formal challenge called an assessment appeal or tax assessment protest. The process and deadline vary by location, but your assessor's office can explain the steps and required documents.
How mill rates change year to year
Mill rates are set during the local government budget process, usually in spring or early summer. The rate reflects how much money the county, city, schools, and other local services need to collect, divided by the total assessed value of all property in that jurisdiction. If the total assessed value in your county rises, the mill rate may stay the same or even drop, because the same revenue is spread across a larger tax base. Conversely, if assessed values fall or local spending increases, the mill rate may rise.
You will see the new mill rate on your property tax bill each year, or you can check your county's published tax rate resolution. Some counties mail a notice of the new rate in advance; others publish it only in the budget document. If you want to know the rate before your bill arrives, contact your tax assessor or check the county website.
What happens when mill rates include multiple levies
In many places, the total mill rate you pay is actually the sum of several separate rates. A typical breakdown might look like this: 8 mills for general county services, 4 mills for schools, 1.5 mills for the fire district, and 0.5 mills for a library district. You add these together to get a total mill rate of 14 mills, then use that total in the calculation.
Your property tax bill usually shows each levy separately so you can see where your money goes. If you want to object to a specific levy — for instance, a new school bond — you may be able to vote on it during a local election or attend a public hearing where the rate is set. The process varies by jurisdiction and type of levy.
Some levies are temporary. A school bond might be set to expire after 10 years, at which point that portion of the mill rate drops off your bill. Check your tax bill or assessor's office to see which levies in your area are permanent and which have an end date.
Common mistakes when calculating property tax
The most common error is forgetting to divide by 1,000. The mill rate is expressed per 1,000 dollars of value, so if you multiply assessed value by mill rate and forget the division step, your answer will be 1,000 times too high. Always divide by 1,000 at the end.
Another mistake is using your home's purchase price or estimated market value instead of the assessed value. These are different numbers, and only the assessed value goes into the calculation. If you are unsure which number is correct, check your most recent property tax bill — the assessed value is always listed there.
A third error is using an outdated mill rate. Rates change annually, so if you are calculating next year's tax based on this year's rate, you may be off. Wait for the new rate to be published, or contact your assessor to confirm the current rate.
Frequently Asked Questions
What does "mill" mean in mill rate?
A mill is one-thousandth of a dollar, or $0.001. A mill rate of 15 mills means $15 per $1,000 of assessed value. The term comes from old currency, but it is still used in property tax calculations across the United States.
Can I reduce my property tax by lowering my assessed value?
You cannot lower your assessed value yourself, but you can challenge it if you believe it is inaccurate. File an assessment appeal with your county assessor, usually within 30 to 45 days of receiving your tax bill. You will need evidence such as recent appraisals or comparable sales data. The assessor will review your claim and may adjust the value if warranted.
Do all properties in my county pay the same mill rate?
Yes, the mill rate is the same for all residential properties in a given county or tax district. However, some properties may be exempt from property tax entirely — for instance, churches, nonprofits, and government buildings. Agricultural land may also have a lower rate in some states.
What if my property is in multiple tax districts?
If your property falls within more than one district — such as a county, school district, and fire district — you pay the combined mill rate of all applicable districts. Your tax bill will show each district's rate separately. The assessor's office can tell you which districts apply to your address.
How often does the assessed value change?
The frequency depends on your state and county. Some places reassess all properties annually; others do it every three to five years. A few states reassess only when a property is sold. Check your county assessor's website or call their office to learn your local reassessment schedule.