What Is Assessed Value? How It Affects Your Property Tax Bill

If you own a home, the term "assessed value" directly controls how much you pay in property taxes every year. Yet most homeowners have only a vague understanding of what it means, how it is determined, and why it might be different from what they think their home is worth. Understanding assessed value is the first step to understanding — and potentially reducing — your property tax bill.

Assessed value vs. market value vs. appraised value

These three terms are often used interchangeably in casual conversation, but they have distinct meanings in the context of property taxes and real estate:

Market value is the most likely price your home would sell for on the open market, given current conditions. It is determined by supply and demand — what a willing buyer would pay a willing seller in an arm's-length transaction. Market value fluctuates constantly with real estate trends, interest rates, and local economic conditions.

Appraised value is a professional estimate of your home's market value, prepared by a licensed real estate appraiser. Appraisals are typically ordered by mortgage lenders during a home purchase or refinance to ensure the property is worth at least as much as the loan amount. The appraiser visits the property, measures it, evaluates its condition, and compares it to recent comparable sales.

Assessed value is the value assigned to your property by your local tax assessor specifically for the purpose of calculating your property tax bill. This is the only one of the three that directly determines how much tax you pay. In some jurisdictions, the assessed value is intended to equal 100% of market value. In others, it is legally set at a fraction of market value through an assessment ratio.

For example, if your home's market value is $400,000 and your jurisdiction uses a 50% assessment ratio, your assessed value would be $200,000. Your property tax is then calculated by applying the tax rate to that $200,000 figure, not the full $400,000.

How assessors determine your property's value

County and municipal assessors are responsible for determining the assessed value of every taxable property in their jurisdiction — which can mean tens of thousands or even hundreds of thousands of individual properties. Given this scale, assessors use a process called mass appraisal rather than individually inspecting every home.

Mass appraisal relies on statistical models that analyze property characteristics and recent sales data across the entire jurisdiction. The assessor's office collects data on each property including:

• Physical characteristics: Square footage, lot size, number of rooms, year built, construction type, and condition.
• Location factors: Neighborhood, school district, proximity to amenities, waterfront or view premiums.
• Sales data: Recent arm's-length sales of similar properties in the area.
• Income potential: For commercial or rental properties, the income the property could generate.
• Replacement cost: How much it would cost to rebuild the structure, less depreciation.

Based on these inputs, the assessor's model produces an estimated market value for each property. Depending on local law, this may be used directly as the assessed value or multiplied by an assessment ratio.

Because assessors are applying models to large groups of properties, individual errors are inevitable. The assessor may have incorrect square footage data, an outdated condition grade, or may not be aware of structural issues that reduce your home's value. This is why the appeals process exists and why it's important to review your property record card for accuracy.

Assessment ratios explained

Not all states assess properties at 100% of market value. The assessment ratio (also called "level of assessment" or "equalization ratio") determines what percentage of market value is used as the taxable base:

• 100% assessment states: California, Florida, Georgia, and many others assess at full market value.
• Fractional assessment states: South Carolina assesses owner-occupied homes at just 4% of market value. Ohio assesses at 35%. New York assessments vary widely by locality, from 1% to 100%.
• Classified assessment states: Some states use different ratios for different property types. For instance, residential property might be assessed at 10% while commercial property is assessed at 25%.

A low assessment ratio doesn't necessarily mean low taxes. States with low assessment ratios typically have higher nominal mill rates to compensate. What matters for your tax bill is the effective tax rate — the combination of assessment ratio and mill rate.

What triggers a reassessment?

Your assessed value doesn't change every day. It is updated based on specific triggers that vary by jurisdiction:

• Scheduled reassessments: Many jurisdictions conduct mass reassessments on a regular cycle — annually, every 2–3 years, or every 4–5 years. Some states like California only reassess when the property is sold (under Proposition 13).
• Property sale: In many jurisdictions, a property sale triggers a reassessment to the purchase price. This is the most common cause of large assessment jumps.
• Building permits: If you pull a permit for a renovation, addition, or new construction, the assessor will update your value to reflect the improvement once the work is completed.
• Zoning changes: If your property is rezoned (for example, from residential to commercial), the assessed value may change to reflect the new use potential.
• Natural disasters: After events like floods, fires, or hurricanes, assessors may temporarily reduce assessed values to reflect damage.
• Market corrections: During significant real estate downturns, some jurisdictions proactively reduce assessed values to reflect falling market conditions.

Assessment caps and limits

Several states have enacted laws that limit how much your assessed value can increase from year to year, regardless of how much the actual market value rises:

• California (Prop 13): Assessed value cannot increase by more than 2% per year, regardless of market appreciation. The property is reassessed to market value only when sold.
• Florida (Save Our Homes): Annual increase limited to 3% or the Consumer Price Index, whichever is lower, for homesteaded properties.
• Texas: Assessment increases on homesteaded properties are capped at 10% per year (recently reduced from 10% to help homeowners with rapidly rising values).
• Michigan: Taxable value cannot increase by more than 5% or the rate of inflation, whichever is less.

These caps benefit long-time homeowners but can create significant tax disparities. Two identical houses next door to each other can have vastly different tax bills if one has been owned for 20 years (with a capped, low assessed value) and the other was recently purchased (assessed at the full purchase price).

How assessed value affects your tax bill

The relationship between your assessed value and your property tax is direct and simple:

If your assessed value increases while the tax rate stays the same, your tax bill goes up proportionally. A 25% increase in assessed value means a 25% increase in your tax bill (before any exemptions).

However, as we discussed in our article on tax rates, the tax rate itself may also change. If all property values in your town rise equally, the local government might lower the tax rate, resulting in a roughly unchanged tax bill. Your individual outcome depends on how your value change compares to the overall community.

What to do if your assessed value seems too high

If you believe your property has been overvalued, you have options:

• Review your property record card for factual errors in square footage, room count, or condition.
• Compare with neighbors: Look up the assessed values of similar homes on your street or in your neighborhood. If comparable homes are assessed significantly lower, you may have grounds for an appeal.
• Request an informal review: Many assessor's offices offer an informal meeting where you can discuss your concerns before filing a formal appeal.
• File a formal appeal: If the informal process doesn't resolve the issue, file a formal appeal before the deadline. See our step-by-step appeal guide for detailed instructions.