How to figure out your assessed value (and spot errors fast)

Last updated 2026-07-09

What is assessed value, exactly?

Assessed value is the number your county assessor puts on your property to calculate how much property tax you owe. It is not market value. It is not the appraised value from your mortgage. It is not what Zillow guesses. Those distinctions cost people money every year.

Market value is what a willing buyer would pay a willing seller in an arm's-length sale. Assessed value is usually a fixed percentage of that market value, set by state law. That percentage has a few names depending on where you live: assessment ratio, assessment level, or assessment rate.

The formula is short:

Assessed Value = Market Value x Assessment Ratio

Say your home's market value is $400,000 and your state assesses residential property at 80%. Your assessed value is $320,000. Your tax bill then comes from multiplying that assessed value by your local mill rate (or tax rate). A higher assessed value means a higher bill, full stop.

A handful of states, including California, Texas, and Illinois, add another layer. They call the figure on your bill the "taxable value" or "equalized assessed value" (EAV), which runs one more multiplier on top of the assessed value. ^[1] More on that below.

Where do you find your assessed value right now?

Four reliable places show your assessed value, and at least one of them works in every county in the country. Your assessment notice, your assessor's website, your tax bill, and the assessor's office itself.

1. Your assessment notice. Counties mail these annually or every other year. It shows market value, assessed value, any exemptions applied, and the deadline to appeal. This is the official document. Keep it.

2. Your county assessor's website. Almost every assessor in a county with more than 50,000 people has an online parcel search. Search by address or parcel ID number (also called an APN, parcel number, or property identification number). The result page usually shows assessed value, the prior year's value, ownership history, and sometimes the comparable sales the assessor used. ^[2]

3. Your property tax bill. The bill itself usually prints both the assessed value and the taxable value. Look for a line labeled "assessed value," "assessment," or "EAV" depending on your state.

4. The assessor's office directly. If records aren't online, a phone call or an in-person visit gets you a printout of your property record card. That card is worth its weight. It lists every physical characteristic the assessor has on file for your home: square footage, bedroom count, garage size, condition grade. Errors on this card are a leading cause of inflated assessments.

For major metro counties, here are direct starting points. Los Angeles County property tax lookups run through the LA County Assessor portal. Cook County tax assessor tax bills include a detailed EAV breakdown. Maricopa property tax records are searchable by address at the Maricopa County Assessor site. And San Diego property tax records appear in the San Diego County Assessor-Recorder-Clerk database.

How do you calculate assessed value from market value?

The math is easy. Knowing your state's assessment ratio is the hard part.

Assessed Value = Market Value x Assessment Ratio

Assessment ratios run from 10% (Alabama assesses residential property at 10% of market value) ^[3] up to 100% in states like California. California layers Proposition 13 on top, capping the taxable base at the purchase price adjusted for no more than 2% annual inflation. ^[4]

Here's how residential assessment ratios compare across a sample of states:

State	Residential Assessment Ratio	Notes
Alabama	10%	Statutory, set by state law
California	100% of purchase price (Prop 13 base)	Annual increase capped at 2%
Colorado	6.7% (2023 session change)	Legislature adjusts periodically
Illinois	33.33% of market value (statewide)	County equalizer then applied
New York (NYC)	6% of market value (Class 1)	Complex class system applies
Texas	100%	But homestead cap limits annual increase
Florida	100%	Save Our Homes caps annual increase at 3%
Georgia	40%	Applies statewide for residential
Arizona	10% (residential)	Separate from LPV calculation

Once you know your ratio, plug in your estimated market value. If the assessor's market value figure looks wrong, that's where you fight. Not the assessment ratio. The ratio is fixed by law, and no board of review can change it.

One thing to keep front of mind: the assessor's market value estimate is an opinion, not a fact. You can beat it with sales data from comparable properties (comps). That's the core of every successful residential appeal. ^[5]

What's the difference between assessed value, market value, and taxable value?

People throw these three terms around as if they mean the same thing. They don't, and the difference is money.

Market value (also called "fair market value" or "full cash value" in some states) is what the assessor thinks your home would sell for on the open market. They reach it with mass appraisal methods: sales of comparable homes, income approaches for rentals, cost approaches for new construction. ^[6]

Assessed value is market value multiplied by the assessment ratio. In a state with a 40% ratio, a $300,000 market value becomes a $120,000 assessed value.

Taxable value is assessed value minus any exemptions. A homestead exemption of $50,000 in Georgia, for example, reduces the taxable base by $50,000, not by $50,000 times the assessment ratio, because Georgia applies exemptions after the 40% assessment. So the order of operations is: market value, then assessment ratio, then exemptions, then the mill rate gives you your tax bill.

Equalized assessed value (EAV), used in Illinois, adds one more step. The Illinois Department of Revenue publishes an "equalization factor" (also called the "multiplier") for each county every year. The Cook County multiplier for 2022 was 3.0027. ^[1] Your assessed value (33.33% of market) gets multiplied by that factor to produce EAV. Then exemptions come off, then the mill rate applies. That's why Illinois bills read like a puzzle.

If you're in a county like Cook, the Cook County tax assessor tax bill page walks through this calculation with real examples.

How does the assessor calculate your property's market value?

Assessors don't walk through every home every year. They run mass appraisal models, statistical tools that estimate market value for thousands of properties at once using sales data, property characteristics, and neighborhood adjustments. ^[6]

There are three main approaches.

Sales comparison approach. The assessor finds recent sales of comparable homes and adjusts for differences in size, condition, age, location, and features. This is the dominant approach for single-family residential property.

Cost approach. The assessor estimates what it would cost to replace the structure, then subtracts depreciation and adds land value. Used more often for new construction and unique properties with few comps.

Income approach. Used mainly for rental and commercial property. The assessor estimates net operating income and capitalizes it at a market cap rate.

Here's the weakness. Mass appraisal can't see inside your house. The assessor doesn't know your kitchen is from 1987, that the roof needs replacing, or that the basement floods every spring. Your property record card reflects the data they have on file, which may be years old and may be wrong.

So request your property record card. If it says 2,400 square feet and you have 1,900, that's a factual error that should get corrected right away, usually without a formal appeal. If the physical data is right but the market value is still too high, you need comps.

For county-specific assessor processes, the Gwinnett County tax assessor, Bexar County tax assessor, and Madison County tax assessor offices all publish property record card lookup tools online.

How do you know if your assessed value is too high?

There are two separate tests, and you only need to pass one of them to win an appeal. Either the market value estimate is too high, or the assessment ratio applied to you is out of line with your neighbors.

Test 1: Is the market value estimate accurate?

Look up three to five homes in your neighborhood that sold in the past 6 to 12 months. Find ones close in size, age, condition, and style. If those homes sold for less than what the assessor thinks your home is worth, you have a valuation argument. Evidence-based and hard to argue with.

Test 2: Is the assessment ratio correctly applied?

This is an equity or uniformity argument. Even if the assessor's market value is right, if your property is assessed at a higher ratio than similar homes, you're overpaying your share. The International Association of Assessing Officers (IAAO) publishes standards on assessment uniformity. ^[7] Many state statutes require assessments to be "uniform and equal" or within a defined ratio range.

Here's the ratio study logic. Divide the assessor's market value estimate for your property by what you believe the actual market value is. If you think your home is worth $350,000 but the assessor pegged it at $420,000, your specific property is assessed at 120% of market. If your neighbors at similar market values sit at 100%, that's a uniformity problem.

Most county assessors post aggregate ratio studies for their jurisdiction. The IAAO standard says residential assessments should fall within a 10% coefficient of dispersion of the median assessment ratio for comparable properties. ^[7]

For Georgia counties, both the Coweta County tax assessor and Cherokee County tax assessor offices publish annual ratio study data and accept appeals on uniformity grounds under O.C.G.A. § 48-5-311. ^[8]

How do you verify your assessed value is correct, step by step?

Work these steps in order. You can finish all of it in an afternoon.

Step 1: Get your assessment notice or find your parcel online. Note the market value, assessed value, and any exemptions shown. Write down your parcel number.

Step 2: Request your property record card. Do this online if available, by phone, or in person. Look for errors in square footage, lot size, bedroom and bathroom count, year built, and condition rating. If you find an error, report it in writing to the assessor's office before doing anything else. Factual corrections often happen without a formal appeal and without a deadline.

Step 3: Check the assessment ratio. Look up your state's statutory assessment ratio (your state's department of revenue or department of taxation website has it). Multiply your estimated market value by that ratio. Compare the result to your assessed value. If the assessor's assessed value is a lot higher, the assessor's market value estimate is the problem.

Step 4: Pull recent comparable sales. Use Zillow, Redfin, Realtor.com, or your county's recorded deed database (free). Filter for sales in the past 6 to 12 months, within a mile or so, similar square footage (plus or minus 20%), similar age. Note the sale prices.

Step 5: Calculate the price per square foot of the comps. Divide each comp's sale price by its square footage. Average those figures. Multiply by your square footage. That's a rough market value estimate. If it lands well below the assessor's market value, you have a case.

Step 6: Note your appeal deadline. This one is non-negotiable. Miss it and you wait another year. Deadlines range from 30 days after the notice is mailed (some states) to a fixed annual date. Your assessment notice prints the deadline. If it doesn't, call the assessor's office or read your state's property tax statute.

Step 7: File your appeal. Most counties let you file online, by mail, or in person. You generally need the parcel number, your contact info, your estimated market value, and a brief reason. The supporting evidence (comps, photos, contractor estimates) comes later, at the hearing.

If you want a structured way to build that evidence package, the TaxFightBack DIY appeal kit walks through each document you'll need, with templates you keep forever.

What assessment ratio does your state use?

Every state sets its assessment ratio by statute or constitutional provision. A few let counties or municipalities set their own. The table above covered a sample. Here's how to find yours.

Your state's department of revenue, department of finance, or property tax division publishes the official ratio. Search your state name plus "assessment ratio" or "assessment level" or "classification ratio."

The Lincoln Institute of Land Policy tracks assessment ratios across all 50 states in its annual "50-State Property Tax Comparison Study," last published with 2022 data. That study found the average effective tax rate on a median-valued owner-occupied home was 1.0% of market value nationally. The range is enormous, from 0.27% in Hawaii to 2.08% in New Jersey. ^[9] The assessment ratio is a big reason why.

A few states worth flagging:

• Illinois: Assessed at 33.33% of market, then an equalization factor (the "multiplier") adjusts assessed value to bring each county toward 33.33%. Cook County's multiplier often tops 3.0, which effectively pushes the taxable base to 100% of market before exemptions. ^[1]

• New York: Uses a class system. Class 1 (1-3 family residential) in New York City is assessed at 6% of market value. Outside the city, municipalities set their own ratios and the state publishes an equalization rate for each. ^[10]

• Texas: Assesses at 100% of market value but prohibits annual homestead increases above 10%. ^[11]

• Florida: Assesses at 100% but caps annual increases at 3% (or the CPI, whichever is lower) under the Save Our Homes amendment for homestead properties. ^[12]

For Georgia's 40% ratio applied across all 159 counties, the Bibb County tax assessor and Lake County property tax pages show how the calculation runs at the local level.

Can your assessed value go up even if your home's market value didn't?

Yes. This one shocks people every year.

In most states, the assessor revalues property on a cycle, annually in some, every three to five years in others. A countywide revaluation adjusts all values at once based on recent market data. If the housing market in your area rose 25% since the last revaluation, every assessment in that county can go up 25%, even if your specific home never changed a nail.

States with caps (California's Prop 13, Florida's Save Our Homes, Texas's 10% homestead cap) limit how much a homestead assessment can rise each year regardless of market movement. But those caps only apply if you have the homestead exemption filed and active. If you bought a house and never filed for homestead status, or if you're a landlord, the caps may not cover you.

There's also "assessment creep" in states that revalue on a cycle. Say your county revalues every four years. In year one after a revaluation, your assessment doubles to catch the market. Even if prices then cool or fall, your assessment holds until the next cycle. You can still appeal on market value grounds. The question is always what the property was worth on the assessment date, not what it's worth today.

The assessment date matters. Most states set value as of January 1 of the tax year. A few use April 1 or another date. If the market dropped sharply after the assessment date but before your notice arrived, you're stuck with the January 1 value for that year.

What errors on a property record card can lower your assessed value?

This is the fastest win in property tax appeals, and it costs nothing to chase.

Here are the errors that quietly inflate assessed value:

• Square footage overcount. The assessor may have logged finished basement space as above-grade living area, or counted a sun room or enclosed porch as heated square footage. Finished basement space is typically valued at 50 to 60% of above-grade space.

• Extra bathrooms or bedrooms. If the record says 4 bedrooms and you have 3, that's padding your value.

• Garage or outbuilding that no longer exists. A demolished detached garage should come off the record.

• Lot size error. Cross-check against your deed or survey.

• Condition or grade error. Assessors assign a quality grade (often A through D, or a numeric scale). If your home is graded "Good" and it's really "Average," that gap can move value hard.

• Improvement year error. If the assessor has a remodel date wrong, thinks an addition happened that didn't, or misses heavy depreciation from deferred maintenance, the value calculation is off.

To challenge a factual error, write to the assessor's office with documentation: photos, the deed for lot size, measurements you took yourself, or a floor plan. Many offices fix these without a hearing. If they don't, you raise the factual error as part of your formal appeal.

How do you use assessed value to estimate what your tax bill will be?

Once you have your assessed value and your local mill rate (tax rate), the math is short.

Property Tax = (Assessed Value - Exemptions) x Mill Rate

Mill rates are expressed as dollars per $1,000 of assessed value (sometimes as a decimal). A mill rate of 20 means $20 per $1,000 of assessed value.

Example: assessed value of $320,000, homestead exemption of $50,000, mill rate of 18.

Taxable value: $320,000 - $50,000 = $270,000 Tax: $270,000 / 1,000 x 18 = $4,860

Find your mill rate on your tax bill, on your assessor's website, or at your local government's budget office. Mill rates change every year. The assessed value holds until the next assessment cycle or until you win an appeal.

Want to model what your bill would look like after a successful appeal? Reduce the assessed value by your estimated reduction, then run the same formula. A $30,000 cut in assessed value at a mill rate of 20 saves you $600 a year. That's $6,000 over a decade, and it compounds, because a lower base is less likely to breach caps down the road.

The St. Louis County personal property tax page shows how one jurisdiction publishes mill rates alongside assessed values.

What should you do after you figure out your assessed value?

If your assessed value looks right and your bill is fair, you're done. File for any exemptions you haven't claimed yet (homestead, senior, veteran, disability) and check back after the next assessment notice arrives.

If your assessed value looks wrong, here's the sequence.

First, decide if the error is factual or valuation-based. Factual errors (square footage, lot size, bedroom count) go to the assessor's office directly and informally. Valuation errors require a formal appeal.

Second, get your appeal in before the deadline. You can always add evidence later. Missing the deadline costs you a full year.

Third, gather comps for the hearing. You want three to five recent sales of similar homes, with addresses, sale dates, sale prices, and square footage. A simple spreadsheet does the job.

Fourth, attend your hearing (or submit evidence by mail if the county allows informal review). Be specific: "The assessor's market value of $420,000 is not supported by the comparable sales in my neighborhood. The three closest sales averaged $362,000." That's the kind of statement a board of review responds to.

For specific county appeal procedures, see our guides for the Gwinnett County tax assessor, Cherokee County tax assessor, and Coweta County tax assessor in Georgia, or the Maricopa property tax appeal process in Arizona.

The TaxFightBack appeal kit gives you a pre-built evidence binder template, comp selection worksheets, and a hearing script, so you keep every dollar of any reduction. No contingency fee. No percentage paid to a firm.

Frequently asked questions

Is assessed value the same as market value?

No. Market value is what your home would sell for. Assessed value is market value multiplied by your state's assessment ratio, which runs from 10% (Alabama) to 100% (Texas). They're only equal in states that assess at 100% with no caps. Your tax bill is based on assessed value, not market value, so the distinction decides what you actually pay.

How do I find my property's assessed value online?

Go to your county assessor's website and use the parcel search tool. Search by street address or parcel ID number. The result page shows your current assessed value, prior year value, and often the assessment history. If your county has no online lookup, call the assessor's office and ask for your property record card. They're required to provide it.

What is an assessment ratio and how do I find mine?

The assessment ratio is the percentage of market value at which your county assesses property. State law sets it, not your local assessor. Find it by searching your state's department of revenue website for 'assessment ratio' or 'classification ratio.' Alabama uses 10%, Georgia 40%, Texas and California nominally 100% with different caps. The ratio ties your assessed value to your home's actual market value.

How do I calculate my property tax from my assessed value?

Subtract any exemptions from your assessed value to get your taxable value. Multiply that by your local mill rate (dollars per $1,000 of value). If your taxable value is $270,000 and your mill rate is 20, your tax is $5,400. Find your mill rate on your tax bill or your local government's finance office website. It changes annually with municipal budget decisions.

What is equalized assessed value (EAV) and how is it different?

EAV is used mainly in Illinois. The state applies an equalization factor (multiplier) to each county's assessed values to bring them closer to a uniform 33.33% of market value statewide. Cook County's 2022 multiplier was 3.0027. Your assessed value (33.33% of market) gets multiplied by that factor to produce EAV. Exemptions then reduce EAV, and the mill rate applies to what remains.

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

Yes. Most counties let homeowners file appeals themselves. You need your parcel number, a written statement of your estimated market value, and supporting evidence, typically three to five comparable sales from the past 6 to 12 months. The process is built to be usable without professional representation, though it does take you gathering and presenting evidence clearly and meeting your county's appeal deadline.

How often does assessed value change?

It depends on your state's revaluation cycle. Some states (Maryland, Texas) reassess annually. Others revalue every three to five years (many Midwest and Southern states). Between revaluations, your assessed value usually holds flat unless you appeal, add improvements, or buy or sell the property. Countywide revaluations can produce big jumps in one year to catch up with market movement.

What errors on a property record card should I look for?

Check square footage (finished versus unfinished space matters), lot size, bedroom and bathroom count, year built, condition or quality grade, and any improvements listed. If the record shows a finished basement you don't have, an extra bedroom, or garage space that was demolished, those are factual errors that inflate value. Report them in writing to the assessor with documentation like photos and measurements before filing a formal appeal.

What is the assessment date and why does it matter?

The assessment date is the point in time the assessor uses to value your property. Most states use January 1 of the tax year. Your appeal must argue the property was overvalued as of that specific date, not as of today. If the housing market dropped after January 1 but before you got your notice, you're still assessed at the January 1 value. Comparable sales used as evidence should sit near that date.

What if my assessed value went up but I didn't make any improvements?

That's normal in states without annual caps. A countywide revaluation updates all values to current market conditions, so your assessment rises with neighborhood prices even if your home hasn't changed. You can still appeal if the assessor's market value estimate sits above what comparable homes actually sold for. The appeal rests on the estimated market value on the assessment date, not on the change itself.

How do I compare my assessed value to my neighbors' assessments?

Most county assessors post all parcel data online in a searchable database. Look up neighboring properties of similar size and age and note their assessed values. If your per-square-foot assessed value runs well above comparable neighboring parcels, that's a uniformity or equity argument you can raise in an appeal. The IAAO standard says assessments should fall within a 10% coefficient of dispersion of the median ratio.

Does a successful appeal permanently lower my assessed value?

For the tax year you appealed, yes. The reduction is locked in for that year. Whether it carries forward depends on your state. In most states, the assessor can revalue the property at the next cycle without being bound by your appeal settlement. Still, a lower base before the next revaluation means any percentage increase applies to a smaller starting number, which produces ongoing savings.

What is the difference between taxable value and assessed value?

Assessed value is market value multiplied by the assessment ratio. Taxable value is assessed value minus any exemptions you qualify for: homestead, senior citizen, veteran, disability, and others. Your tax bill is calculated on taxable value, not assessed value. The distinction matters because an exemption cuts your bill without changing the assessor's opinion of market value.

Sources

1. Illinois Department of Revenue — Property Tax: Equalizers by County: Cook County equalization factor (multiplier) for 2022 was 3.0027, applied to assessed values set at 33.33% of market value
2. National Association of Counties — County Assessors and Property Tax Administration: County assessors maintain parcel databases accessible to the public, typically including assessed value, ownership, and property characteristics
3. Alabama Department of Revenue — Property Tax Division: Assessment Ratios: Residential property in Alabama is assessed at 10% of market value under state law
4. California State Board of Equalization — Proposition 13 Overview: California's Proposition 13 limits annual increases in assessed value to 2% and bases assessments on purchase price
5. International Association of Assessing Officers (IAAO) — Standard on Mass Appraisal of Real Property: Comparable sales data is the primary method for challenging market value estimates in residential assessment appeals
6. International Association of Assessing Officers (IAAO) — Standard on Mass Appraisal of Real Property: Mass appraisal models use statistical analysis of sales data and property characteristics to estimate market value for large numbers of properties
7. International Association of Assessing Officers (IAAO) — Standard on Ratio Studies: IAAO standard requires residential assessments to fall within a coefficient of dispersion (COD) of 10% or less of the median assessment ratio
8. Georgia General Assembly — O.C.G.A. § 48-5-311, Property Tax Appeals: Georgia Code § 48-5-311 governs the property tax appeal process, including grounds of uniformity and fair market value for residential properties in all 159 counties
9. Lincoln Institute of Land Policy — 50-State Property Tax Comparison Study (2022 data): Average effective property tax rate on a median-valued owner-occupied home was 1.0% nationally, ranging from 0.27% in Hawaii to 2.08% in New Jersey
10. New York City Department of Finance — How We Assess Property: Class 1 properties (1-3 family residential) in New York City are assessed at 6% of market value under the city's property classification system
11. Texas Comptroller of Public Accounts — Property Tax Basics: Appraisal Caps: Texas law prohibits annual homestead appraised value increases of more than 10% over the prior year's appraised value
12. Florida Department of Revenue — Property Tax: Save Our Homes Assessment Limitation: Florida's Save Our Homes amendment caps annual assessment increases on homestead property at 3% or the CPI, whichever is lower