How the Calculation Works: Assessed Value and Mill Rates
Every property tax bill starts with two numbers: your home's assessed value and your jurisdiction's tax rate. Multiply them together and you get your annual tax liability.
Assessed value is determined by a local government assessor, who uses property characteristics — square footage, lot size, age, condition, and comparable sales — to estimate a taxable value for your home. Importantly, assessed value is not always the same as market value. Many jurisdictions apply an assessment ratio — for instance, taxing at 80% of estimated market value. If your home is worth $400,000 on the market and your locality assesses at 80%, your assessed value would be $320,000.
Tax rates are typically expressed as mill rates. One mill equals $1 of tax for every $1,000 of assessed value. A mill rate of 25 on a $320,000 assessed value produces a $8,000 annual tax bill. Local governments set mill rates each budget cycle based on how much revenue they need to fund services.
$3,901
Average annual property tax paid by U.S. homeowners
According to U.S. Census Bureau American Community Survey data, this figure varies dramatically by state — from under $1,000 in some low-tax states to over $10,000 in high-cost jurisdictions.
1.1%
Effective property tax rate national average
ATTOM Data Solutions has tracked the U.S. average effective property tax rate — taxes paid as a share of home value — at roughly this level in recent years, though state-level rates range from well below to well above this figure.
~40%
Share of homeowners who may be over-assessed
Industry estimates suggest a substantial portion of residential properties carry assessed values higher than what comparable market sales would support, though this varies widely by market.
What Factors Can Change Your Bill
Several forces can push your property tax bill up or down from year to year.
- Reassessment: When your locality reassesses properties — whether annually or on a multi-year cycle — a rising real estate market can lift assessed values across the board, increasing bills even if the mill rate stays flat.
- Local budget decisions: If a school district or municipality increases its budget, it may raise the mill rate to generate additional revenue, directly affecting what homeowners owe.
- Property improvements: Adding livable square footage, a garage, or a pool typically raises your assessed value at the next reassessment.
- Exemptions gained or lost: Qualifying for — or losing eligibility for — a homestead, senior, or disability exemption changes your taxable base. See our overview of how homestead exemptions work and who typically qualifies for details on reducing your taxable value through these programs.
Review Your Assessment Notice Every Year
Local assessors are required to notify homeowners of changes to their assessed value. When you receive the notice, compare the assessed value against recent comparable sales in your neighborhood. If the figure seems high, you typically have a limited window — often 30 to 90 days — to file an appeal, so don't set the notice aside.
Exemptions: Reducing What You Owe
Exemptions are one of the most accessible — and underused — tools for lowering a property tax bill. They reduce the assessed value on which taxes are calculated, rather than the tax rate itself.
The homestead exemption is the most common. Available in most states, it reduces the taxable assessed value of a primary residence by a set dollar amount or percentage. A homeowner whose assessed value is $300,000 and who qualifies for a $50,000 homestead exemption would only be taxed on $250,000. Learn how to find out whether you qualify for a homestead exemption and what the application typically involves.
Other common exemptions include those for seniors on fixed incomes, veterans, people with disabilities, and agricultural land. Eligibility requirements and benefit amounts vary considerably by state and county, so checking directly with your local assessor's office is essential.
When Your Assessment Is Wrong — and What to Do
Assessors work with imperfect data, and errors happen. Your assessment might reflect incorrect square footage, an overestimate of condition, or a failure to account for a market downturn since the last sales comparison. If your assessed value appears inflated relative to what you could realistically sell the home for, you have the right to appeal.
The appeals process typically begins with an informal review — a conversation with the assessor's office where you present evidence such as recent comparable sales, an independent appraisal, or documentation of property defects. If that doesn't resolve the dispute, most jurisdictions have a formal review board or tax tribunal. Our detailed guide on what the property tax appeal process actually looks like walks through the typical steps and the evidence that tends to carry weight.
Property Tax Rules Vary Significantly by State
There is no single national standard for how property taxes are assessed, collected, or appealed. Some states have strict assessment caps (like California's Proposition 13), while others reassess annually at full market value. Always verify the specific rules, deadlines, and exemption programs that apply in your county or municipality.
This article is for general informational purposes only and does not constitute legal, financial, or tax advice. Property tax rules vary significantly by state and locality. Consult a qualified tax professional or attorney for guidance specific to your situation.
Frequently Asked Questions
Your bill is calculated by multiplying your home's assessed value by the local mill rate or tax rate. For example, if your assessed value is $300,000 and the mill rate is 20 mills ($20 per $1,000), you would owe $6,000 annually. Exemptions can reduce the assessed value before the rate is applied.
Market value is what your home would likely sell for on the open market. Assessed value is the figure a local assessor assigns for tax purposes, which may be a percentage of market value depending on your jurisdiction. The two numbers can diverge significantly, especially when property values change faster than reassessment cycles.
Yes, in several ways. You can apply for exemptions you qualify for — such as homestead, senior, or veteran exemptions — and you can file an appeal if you believe your assessed value is too high. Successfully challenging an inflated assessment can reduce your bill going forward.
Reassessment schedules vary widely by jurisdiction — some localities reassess annually, others every few years, and some only when a property is sold. Check with your local assessor's office to understand the cycle in your area.
Unpaid property taxes accrue penalties and interest. If left unresolved, a local government can place a tax lien on your property and, in serious cases, eventually initiate a tax sale. Timelines and processes differ by state and locality.
Generally, yes. Significant improvements — such as adding a bedroom, finishing a basement, or building an addition — can increase your assessed value at the next reassessment, resulting in a higher tax bill. Routine maintenance and cosmetic repairs typically have little or no effect.
The content on this site is provided for informational purposes only and should not be considered a substitute for professional advice. While we strive to provide accurate and up-to-date information, we make no guarantees regarding its completeness or accuracy. Always consult a qualified professional for advice specific to your circumstances before making any decisions.