How to calculate assessed value of your property (and check it)

Last updated 2026-07-09

What is assessed value and how is it different from market value?

Assessed value is the dollar figure your local government uses to calculate your property tax bill. Market value, sometimes called fair market value, is the price a willing buyer and a willing seller would agree on in an arm's-length sale. Those two numbers are often far apart. Confusing them is the most common mistake homeowners make when they read a tax notice.

Every jurisdiction sets an assessment ratio, also called an assessment level or assessment rate. That ratio is the fraction of market value at which the assessor is supposed to value property for tax purposes. In California, Proposition 13 caps the assessed value at the purchase price plus a maximum 2% annual increase, so a home bought decades ago can carry an assessed value far below current market value ^[1]. In New York City, Class 1 residential property is assessed at 6% of market value ^[2]. In Texas, assessed value is supposed to equal 100% of market value, and Texas Tax Code Section 23.01 states that "all taxable property is appraised at its market value as of January 1" ^[3].

The terminology shifts from state to state. Some say "assessed value." Others say "appraised value" (Texas), "equalized value" (Wisconsin), or "taxable value" (Michigan). The math underneath is the same. Start with market value, apply a ratio, multiply by the tax rate.

How do you calculate assessed value from market value?

The formula is short.

Assessed Value = Market Value x Assessment Ratio

Say your county assesses at 80% of market value and a comparable home just sold for $350,000. The assessed value would be $350,000 x 0.80 = $280,000.

Finding your local assessment ratio is the step most guides skip. Three places hold the answer:

1. Your state's department of revenue or department of taxation website. Most publish the legally required assessment ratios by property class. 2. Your county assessor's website. Many post the current "equalization rate" or "assessment level" right on the homepage. 3. Your property's record card (also called the property data sheet or parcel detail). It usually shows both the market value estimate and the assessed value, so you can back-calculate the ratio.

Here's why the gap matters. If your state legally requires 100% assessment but your county is actually assessing at 85%, that spread tells you something. It may mean other homeowners are getting a better deal than you, or it may mean your own assessment is off. Some states publish an "equalization ratio" every year to capture exactly this kind of drift between what the law says and what assessors actually do ^[4].

One more wrinkle. Some jurisdictions calculate a "limited" or "capped" assessed value after applying market value and the statutory ratio. Michigan caps the annual increase in taxable value at 5% or the rate of inflation, whichever is lower, under the Headlee Amendment ^[5]. So your market value and your assessed value can drift apart over time even when no assessment ratio changes.

Assessment ratios by state: what fraction of market value does your county use?

Assessment ratios vary enormously. The table below shows the legally mandated assessment ratio for residential property in a selection of states. Actual ratios can deviate from the mandate, and your state equalization report shows the real-world figure.

State	Mandated Assessment Ratio (Residential)	Notes
California	Purchase price + max 2%/yr	Prop 13 acquisition-value system [1]
Texas	100% of market value	Homestead capped at 10% annual increase per TX Tax Code §23.23 [3]
New York (NYC)	6% (Class 1)	Set by NYC Admin Code §1805 [2]
Illinois	33.33% statewide (Cook County: 10% residential)	Cook County Assessor publishes annually
Florida	100% (Just Value)	Save Our Homes caps annual increase at 3% or CPI [6]
Michigan	50% of market value (State Equalized Value)	Taxable value further capped by Headlee [5]
Massachusetts	100% (full and fair cash value)	Assessors must update every 3 years
Colorado	6.95% (residential, 2023 levy year)	Set under TABOR and SB23-108 [7]

Colorado shows how sharply these rates can move. The residential rate was 7.15% in 2022, dropped to 6.765% for 2023, and the legislature has adjusted it repeatedly to hold down tax bills after fast home price growth ^[7]. Check your state's current published rate before you do any math. Skipping that step is how people appeal against the wrong number.

Metro areas add their own rules on top. NYC property tax runs on a four-class system with a different ratio for each class. LA County property tax follows California's Prop 13 acquisition-value model. Miami-Dade property taxes follow Florida's 100% just-value standard with the Save Our Homes cap layered on top.

How do you calculate property tax from assessed value?

Once you have the assessed value, the tax calculation uses the mill rate (sometimes called the millage rate).

Annual Property Tax = (Assessed Value / 1,000) x Mill Rate

One mill equals $1 of tax per $1,000 of assessed value. If your assessed value is $280,000 and your total mill rate is 25 mills:

$280,000 / 1,000 = 280 280 x 25 = $7,000 annual property tax

Your mill rate sits on your tax bill or on the county treasurer's website. It is not a single rate. It is the sum of rates from every taxing district that overlaps your parcel: county, municipality, school district, fire district, library district, and more. The school district portion is usually the biggest slice, often 60% to 70% of the total.

Some jurisdictions skip the mill rate language and publish an "effective tax rate" as a percentage of assessed value. The math is the same. An effective rate of 2.5% on a $280,000 assessed value produces the same $7,000 answer.

Exemptions cut the assessed value before you apply the mill rate. A $50,000 homestead exemption on that $280,000 assessed value brings the taxable base down to $230,000, and 25 mills on that lower number gives you $5,750 instead of $7,000. That is $1,250 in savings from a single exemption, every year. Property tax taxation basics covers the full exemption menu worth claiming.

How to find your current assessed value without waiting for the mail

You don't need to wait for your assessment notice. Almost every county in the country runs an online parcel search tool.

Go to your county assessor's website and search by address or parcel number. The result page, often called the property record card or parcel detail, shows the assessor's estimate of market value, the assessed value, the property class, and often a breakdown of land value versus improvement value. Print or save that page now. You need it for any appeal.

If your county has no online tool (rare, but it still happens in some rural counties), call the assessor's office. They have to tell you your assessed value. It's public record.

County by county: Santa Clara property tax records are searchable through the Santa Clara County Assessor's portal. Contra Costa County property tax parcels sit in the county's online assessment lookup. San Mateo County property tax records live at the San Mateo County Assessor-County Clerk-Recorder site. Hennepin County property tax records, including estimated market value and taxable value, are in the county's property information search. Williamson County property tax and Collin County property tax parcels are searchable through each county's central appraisal district in Texas.

What does the assessor use to estimate market value in the first place?

The assessor doesn't visit every property every year. For most residential parcels, the market value estimate comes out of a mass appraisal model, a statistical routine that groups similar properties and applies value adjustments from recent sales ^[8].

Three classic approaches drive that model:

Sales comparison approach. The assessor finds recent sales of comparable properties (comps) and adjusts for differences in size, age, condition, and features. This is the workhorse for single-family homes.

Cost approach. The assessor estimates what it would cost to rebuild the structure today, subtracts depreciation, and adds land value. Useful for new construction or unusual properties with few comps.

Income approach. Used mostly for rental and commercial property. The assessor capitalizes the property's net operating income at a market cap rate to reach a value. If an assessor applies this to your rental, they're modeling your rent roll and expense ratios whether they've seen the real ones or not.

Mass appraisal is fast and imprecise. The International Association of Assessing Officers (IAAO) standard for an acceptable ratio study says the median ratio of assessed value to sale price should fall between 90% and 110%, with a coefficient of dispersion below 15% for residential property ^[8]. That's a wide band. A home can sit 10% high and still clear IAAO standards, which is exactly why individual appeals matter.

The model also runs on the data the assessor has on file about your home: square footage, bedroom and bathroom count, year built, lot size, garage, basement finish. If any of that data is wrong, your assessed value is wrong. Checking your property characteristics is step one of any appeal.

How do you check whether your assessed value is accurate?

Pull your property record card and read every field. Square footage, bedroom count, bathroom count, lot size, year built, basement finish, garage size. Errors are common. A database might show 2,200 square feet when your home is 1,950, or list a finished basement you've never had. Those errors push your assessed value straight up.

Then test the implied market value against recent sales. Take the assessed value, divide by the assessment ratio, and you get the assessor's implied market value. If your assessed value is $280,000 and the ratio is 80%, the assessor thinks your home is worth $350,000. Pull three to five recent sales of similar homes from the past 6 to 12 months, ideally within a mile. If comparable homes are selling for $310,000 to $320,000, your $350,000 implied value is off by roughly 10%. That's a real appeal.

This comp analysis is the evidence an appeal board wants to see. TaxFightBack's appeal kit walks you through building a comparable sales grid that assessors and boards actually respond to, formatted the way each state's board expects it.

The deadline matters as much as the evidence. Most states give you 30 to 90 days from the date your assessment notice is mailed to file. Miss that window and you usually wait a full year ^[9]. Check your notice for the exact date. Don't trust a general rule of thumb.

How does the assessment ratio affect your appeal strategy?

If your state's legal ratio is 100% but comparable homes near you are actually assessed at 85% of their sale price, you're over-assessed relative to your neighbors even when the assessor's market value estimate looks about right. This is an equity argument, and it's valid appeal ground in most states ^[9].

To build one, you need the assessment ratios on recent sales near you. Take several homes that sold in the past year, find their assessed values in the public record, and divide assessed value by sale price for each. If those ratios average 85% and yours is 98%, you have an equity case on top of any market value case.

Some states formalize this through equalization. New York publishes an equalization rate for each municipality every year. If a town's equalization rate is 72%, a property assessed at $200,000 is being treated as having a market value of $200,000 / 0.72 = $277,778 for cross-town comparisons ^[4]. Learning your state's equalization system tells you whether you're being assessed fairly against everyone else.

Acquisition-value states like California limit the equity argument by design. The system is built to give identical homes different assessed values based on when each one was bought. The appeal strategy there turns almost entirely on whether current market value has dropped below the Prop 13 base-year value, which triggers a temporary cut called a Proposition 8 decline-in-value review ^[1].

What exemptions reduce your assessed value or tax bill?

Exemptions are the most underused tool in property tax. Two kinds exist: those that cut the assessed value before you calculate tax, and those that apply a credit straight to the bill.

The homestead exemption is the most widespread. It knocks a flat dollar amount off your assessed value. Texas offers a $100,000 homestead exemption on school district taxes as of 2023, raised from $40,000 by legislation in the 88th Legislature ^[3]. Florida's homestead exemption reaches $50,000 on assessed value for most homeowners ^[6]. Illinois's general homestead exemption cuts equalized assessed value by $10,000 in Cook County, with a senior freeze available on top of that.

Other common exemptions cover seniors, veterans with service-connected disabilities (often a full exemption), surviving spouses of veterans, agricultural use, and in some states first-time buyers. Each has its own application deadline, and missing it usually costs you the exemption for a full year.

None of these apply automatically. You have to file, usually with your county assessor or property appraiser. The application is generally one page. The savings can run into thousands of dollars a year, every year, for as long as you own the home. That's real money to leave on the table over a form you didn't send.

Step-by-step: calculate your assessed value and estimated tax bill right now

Here's the whole process from scratch.

Step 1: Find your property record card. Go to your county assessor's website, search your address, and open your parcel detail. Note the market value estimate and the current assessed value.

Step 2: Verify your property characteristics. Check square footage, bedroom and bathroom count, year built, and lot size against what you know about your home. Flag any errors.

Step 3: Find your assessment ratio. Look it up on your state's department of revenue website, or read the ratio your own parcel card implies (assessed value divided by market value).

Step 4: Verify the math. Market value x assessment ratio should equal assessed value. If it doesn't, call the assessor's office and ask why.

Step 5: Find your mill rate. It's on your most recent tax bill, or on the county treasurer's or auditor's website. Make sure you have the total combined rate.

Step 6: Apply any exemptions. Subtract your homestead exemption (or any other exemption you qualify for) from the assessed value to get taxable value.

Step 7: Calculate. (Taxable Value / 1,000) x Mill Rate = Annual Tax. If your taxable value is $230,000 and your mill rate is 25, your annual bill is $5,750.

Step 8: Sanity-check against recent sales. Divide your assessed value by your assessment ratio to get the implied market value. Compare it to recent comparable sales. If the implied market value runs more than 5% to 10% above what comparable homes actually sell for, you have grounds to appeal.

Found a real discrepancy? Build a properly formatted appeal packet instead of handing a contingency firm 25% to 40% of your savings. TaxFightBack's DIY appeal kit gives you the exact forms and comparable sales grid for your state.

Common mistakes homeowners make when calculating or checking assessed value

Confusing market value with assessed value tops the list. They're different numbers, and treating them as one leads you to the wrong conclusion about whether you're over-assessed.

Using list prices instead of sale prices for comps. A Zestimate or a listing price tells you nothing about what buyers actually paid. You need recorded sale prices from deed records or your county assessor's sales database. Many county parcel search tools include a recent sales tab.

Ignoring the exemption you already have (or don't). Some homeowners assume the homestead exemption kicked in automatically at closing. It often didn't. Check your parcel card for a line that reads "homestead exemption" or "HE" and confirm it shows a dollar amount.

Missing the appeal deadline. This happens constantly. The notice says you have 45 days. It lands on the counter and gets forgotten. Forty-six days later the window is shut for a year ^[9]. Set a calendar reminder the day the notice arrives.

Using the wrong year's values. Assessment notices for taxes payable in 2025 are typically based on values as of January 1, 2025 (or January 1, 2024, depending on the state's lag). Match your comps to the relevant valuation date, not today.

Skipping the property class. Some jurisdictions use different assessment ratios or mill rates for residential, commercial, and agricultural property. If your home is misclassified, the assessment is wrong at the foundation, and a reclassification request is a different filing from a value appeal.

What happens to your assessed value when property prices drop?

Assessors move faster to raise assessed values in a hot market than to lower them when prices fall. Part of that is lag, since mass appraisal models run on prior-year data. Part of it is revenue, since lower assessments mean lower collections.

In most states, when the market declines you can appeal for a reduction, and the assessor has to lower the assessed value to reflect current conditions. In California, Proposition 8 lets the assessor temporarily reduce assessed value below the Prop 13 base-year value when market value drops under that base ^[1]. Homeowners who won Prop 8 reductions during the 2008 to 2012 downturn sometimes watched their values snap back to the Prop 13 base when prices recovered, with little warning.

Cap states create a stranger situation. Under Florida's 3% Save Our Homes cap ^[6], Michigan's Headlee cap ^[5], or Texas's 10% homestead cap ^[3], the assessed value may already sit below market value because of the cap. A market decline might not change your assessment at all until market value falls below the capped assessed value.

The practical takeaway: a drop in your neighborhood doesn't flow through to a lower tax bill on its own. You usually have to apply for a reduction or file an appeal with supporting comparable sales.

Frequently asked questions

How do you calculate assessed value if I only know the tax bill amount?

Work backward from the bill. Take the annual tax amount, divide it by your mill rate in decimal form (25 mills = 0.025), and you get the taxable assessed value. If exemptions apply, add them back to reach the full assessed value. A $5,750 tax bill at a 25 mill rate implies a taxable assessed value of $230,000. Add a $50,000 exemption and the gross assessed value is $280,000.

Is assessed value the same as appraised value?

Usually not, and the terminology varies by state. In Texas, the appraisal district sets an "appraised value" meant to equal 100% of market value, then applies exemptions to reach the taxable value. In most other states, "appraised value" means a private appraiser's market opinion, while "assessed value" is the assessor's taxable figure after applying the assessment ratio. Check which definition your state uses before you compare numbers.

Can assessed value be higher than market value?

Yes, and that's the core reason to appeal. If your assessor estimates market value at $350,000 but comparable homes sell for $310,000, your assessed value rests on an inflated market estimate. Even if the assessment ratio was applied correctly, the starting number was wrong. Over-assessment relative to real market value is the most common and most winnable appeal argument.

How often is assessed value recalculated?

It depends on the state. Some reassess annually (Texas appraises every year as of January 1). Others run on a cycle: Massachusetts requires full reassessment at least every three years. California triggers reassessment only at sale or new construction. Many counties do annual statistical updates using sales data between full reappraisals. Check your county assessor's site for the current reappraisal cycle.

How do I calculate property tax on a home I'm about to buy?

Find the current assessed value on the public parcel record for the home you're considering. In most states a sale triggers reassessment to the sale price, so use the purchase price as your expected market value and multiply by the assessment ratio. Then apply the mill rate. In California, use the purchase price as the new Prop 13 base. Ask the county for the exact mill rate on that parcel, since it varies by school and special district boundaries.

What is the assessment ratio and where do I find it for my county?

The assessment ratio is the fraction of market value at which property is taxed. State law sets it, and it runs from under 10% (Colorado residential near 6.95% in 2023) to 100% (Texas, Florida). Find it on your state department of revenue website under property tax assessment guidelines, or back-calculate it from your own parcel card by dividing the assessed value by the assessor's market value estimate.

Does a higher assessed value always mean a higher tax bill?

Generally yes, but not always by as much as you'd expect. If assessed values rise uniformly across the county and the local government cuts the mill rate to collect the same total revenue, individual bills may barely move. This happens often after mass reassessments. Your bill depends on both the assessed value and the mill rate, and governing bodies set mill rates at budget time. Watch both numbers, more than the assessed value.

How does the homestead exemption affect my assessed value calculation?

A homestead exemption cuts the assessed value before the tax rate applies. If your assessed value is $300,000 and you have a $50,000 homestead exemption, you pay tax on $250,000. At a 25 mill rate, that's $1,250 in savings ($300k taxable = $7,500; $250k taxable = $6,250). You have to apply, since it's almost never automatic. Deadlines vary by state but often land in spring.

What data does the assessor use to calculate my home's market value?

Assessors run a mass appraisal model that pulls from property record data (square footage, bedroom count, year built, lot size, condition class) and recent comparable sales. The model groups similar properties and applies market-derived adjustments. The IAAO sets professional standards requiring the median ratio of assessed to sale value to land between 90% and 110% for residential property. Errors in your property data file push your assessed value up or down directly.

Can I lower my assessed value without hiring a property tax attorney?

Yes, and many homeowners do it. The process runs on recent comparable sales, a check of your property record card for data errors, a standard appeal form, and your evidence in front of the review board. Most appeal boards are built to handle self-represented homeowners. Contingency firms typically take 25% to 40% of any first-year savings. A DIY approach keeps all of that money in your pocket.

How do special assessment districts affect my tax calculation?

Special assessment districts (fire, sewer, lighting, stormwater, and so on) add levies on top of your base property tax. Some calculate on assessed value with their own mill rate. Others charge flat fees per parcel or per front foot of lot. They show up as separate line items on your bill. The appeal path for special assessments is often separate from the general assessment appeal and usually runs through the district board, not the county assessor.

If I renovate my home, will the assessed value go up?

Yes. In most states a building permit for substantial renovation triggers reassessment of the improved portion. In acquisition-value states like California, permitted improvements get added to the Prop 13 base value at their construction cost. In annual-assessment states like Texas, the full property is reappraised the following January 1 to reflect the added value. Cosmetic work without permits often goes undetected, though that creates its own legal and insurance problems.

What is equalized assessed value and how is it calculated?

Equalized assessed value (EAV) is the assessed value adjusted by a state equalization factor to bring all local assessments to a uniform percentage of market value statewide. Illinois uses EAV heavily. If a county assesses at 28% of market value instead of the required 33.33%, the state applies a multiplier (33.33/28 = 1.19) to every assessment in that county. Your EAV is what the state and school districts use to calculate tax distributions.

Sources

1. California State Board of Equalization, Proposition 13 Overview: California's Proposition 13 caps assessed value at the purchase price plus a maximum 2% annual increase; Proposition 8 allows temporary reductions when market value falls below base-year value.
2. New York City Department of Finance, Property Tax Classes and Assessment: NYC Class 1 residential property is assessed at 6% of market value under the four-class system set by the NYC Administrative Code.
3. Texas Comptroller of Public Accounts, Property Tax: Texas Tax Code Section 23.01 requires appraisal at 100% of market value as of January 1; the 2023 homestead exemption was raised to $100,000 on school district taxes; homestead assessed value increases are capped at 10% annually under Section 23.23.
4. New York State Department of Taxation and Finance, Property Taxes: New York publishes annual equalization rates per municipality so that assessed values can be compared across jurisdictions at a uniform percentage of market value.
5. Michigan Department of Treasury: Michigan caps annual increases in taxable value at 5% or the rate of inflation, whichever is lower, under the Headlee Amendment; State Equalized Value is set at 50% of market value.
6. Florida Department of Revenue, Property Tax Oversight: Florida assesses property at 100% just value; the Save Our Homes amendment caps annual increases in assessed value for homestead properties at 3% or the CPI, whichever is lower; the homestead exemption is $50,000.
7. Colorado Department of Local Affairs, Division of Property Taxation: Colorado's residential assessment rate was adjusted by SB23-108 and related legislation; the rate for the 2023 levy year was 6.95%, down from 7.15% in 2022.
8. International Association of Assessing Officers (IAAO), Standard on Ratio Studies: IAAO standards require that for residential property the median ratio of assessed value to sale price fall between 90% and 110%, with a coefficient of dispersion below 15%.
9. Lincoln Institute of Land Policy: Most states allow 30 to 90 days from the mailing of the assessment notice to file an appeal; missing this deadline typically requires waiting a full additional year; equity arguments based on assessment ratio disparities are valid grounds in most states.