How to determine your property's assessed value (and what to do if it's wrong)

Last updated 2026-07-09

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

Assessed value is the number your county assessor puts on your property to calculate your tax bill. Market value is what a willing buyer would pay a willing seller today. The two are related, but they're almost never the same figure.

Most states run market value through an assessment ratio to get assessed value. Say your home's market value is $400,000 and your state's residential ratio is 80%. Your assessed value is $320,000. The county then multiplies that by the local mill rate to produce your tax bill.

Some states don't chase market value every year. California under Proposition 13 caps annual increases at 2% until the property sells ^[1]. A neighbor who bought a decade ago might carry a far lower assessed value than you, even in an identical house on the same street.

Appraised value is a third number. A licensed appraiser sets it, either one you hire or one your lender orders. It estimates market value but has no direct effect on your tax bill unless you bring it to an appeal as evidence.

Here's the rule that matters. Your assessed value drives your tax bill. Your market value is the yardstick for checking whether that assessed value is fair. Your appraised value is optional ammunition you can carry into a hearing.

How do assessors actually calculate assessed value?

Assessors use one or more of three methods. Knowing which one applies to your property tells you where to hunt for errors.

The sales comparison approach is standard for most homes. The assessor pulls recent sales of comparable properties nearby, adjusts for size, age, condition, and features, and lands on an estimated market value. That number gets multiplied by the local assessment ratio ^[2]. If the comps are cherry-picked, stale, or drawn from a nicer neighborhood, your assessed value can be off by tens of thousands of dollars.

The cost approach estimates what it would cost to rebuild the structure today, subtracts depreciation, and adds land value. Assessors reach for it on newer homes, unusual properties, or places with thin sales data. The weakness is depreciation. It runs on schedules, not on reality. A house with a cracked foundation doesn't depreciate on paper the way it does in the ground.

The income approach is for income-producing property: apartments, commercial buildings, retail centers. The assessor estimates net operating income and capitalizes it at a market cap rate. Own a small rental? If the assessor assumed a vacancy rate or expense ratio that's wrong, your assessed value can be inflated. Our guides on los angeles county property tax and maricopa property tax show how big counties handle this in practice.

Most jurisdictions today run computer-assisted mass appraisal (CAMA) software that applies statistical models to thousands of parcels at once ^[3]. These models are accurate on average and wrong in individual cases all the time. Unusual homes, deferred maintenance, houses on busy roads the model doesn't penalize enough. That's where the money hides.

What is an assessment ratio, and how does it affect your tax bill?

The assessment ratio is the share of market value your jurisdiction officially uses as the taxable base. A 100% ratio means assessed value is supposed to equal full market value. A 10% ratio (like Cook County, Illinois uses for residential property) means the assessor targets 10% of market value, then applies a higher tax rate to make up the difference ^[4].

This is where homeowners get fooled. Say your state uses an 80% ratio and the assessor puts $450,000 on your $500,000 home. That feels high. It isn't. The correct assessed value is $400,000 (80% of $500,000), so $450,000 is actually too high, but only by $50,000, not the $450,000 sticker that scared you. You have to know your ratio before you can judge your number.

Here's how several large states structure residential assessment ratios:

State	Residential Assessment Ratio	Notes
California	~1% of purchase price (base)	Prop 13 caps annual increase at 2% [1]
Illinois (non-Cook)	33.33% of market value	Set in 35 ILCS 200/9-145 [4]
Cook County, IL	10% residential / 25% commercial	See cook county tax assessor tax bill
Texas	100% (appraised value)	Increases capped at 10%/yr for homestead [5]
Georgia	40% of fair market value	Set in O.C.G.A. § 48-5-7 [6]
New York	Varies by class and municipality	Class 1 (1-3 family) often 6% in NYC
Arizona	10% residential, 18% commercial	A.R.S. § 42-15001 [7]

Once you know your ratio, the math is short. Divide your assessed value by the ratio to get the market value the assessor is asserting. Then ask whether that number matches what your home would actually sell for.

Where can you find your current assessed value?

You have three reliable places to look, and they don't all show up at the same time.

Start with your annual assessment notice. Every jurisdiction mails one, usually between January and May, though timing varies by state. It states your assessed value, the assessment ratio, your exemptions, and your deadline to appeal. Read it the day it lands. That deadline is real and most states grant no extensions ^[2].

Next, your county assessor's website. Nearly every major county now runs a searchable parcel database. Enter your address and you get your current assessed value, prior years, and often the property record card showing what the assessor thinks your square footage, bedroom count, and condition rating are. That record card is gold. Factual errors on it are the easiest appeals to win.

For specific county portals, see our guides for bexar county tax assessor, gwinnett county tax assessor, san diego property tax, and lake county property tax.

Last, your tax bill. It arrives separately from the assessment notice, usually in the fall, and shows the assessed value used to calculate that year's tax. Here's the trap. By the time the bill reaches you, the appeal window for that cycle has often already closed. Don't wait for the bill to sound the alarm.

How do you calculate what your assessed value should be?

This is the heart of a DIY appeal. You're not guessing. You're running the same math the assessor ran, with better data about your specific house.

Step 1: Find your state's assessment ratio. Your county assessor's site lists it, or check your state department of revenue. Georgia is 40% ^[6]. Arizona residential is 10% ^[7]. Texas is 100% ^[5].

Step 2: Estimate your home's true market value. The most defensible route is the sales comparison approach using your own comps. Pull three to six sales of homes like yours in size, age, condition, and neighborhood, closed in the past six to twelve months. Zillow, Redfin, and your county's recorded deed database all carry this data. The assessor's own sales database is often on their portal and carries extra weight because it's their source.

Step 3: Adjust for differences. Your house has 1,800 square feet. A comp sold at $380,000 but has 2,000 square feet. Adjust that comp down. A common residential adjustment is $75 to $150 per square foot depending on your market, but check what recent local sales actually support before you commit to a number.

Step 4: Average your adjusted comps to get an indicated market value. Multiply that by your state's assessment ratio. The product is your calculated correct assessed value.

Step 5: Compare it to your current assessed value. If the assessor's number sits more than 10 to 15% above yours, you likely have a winnable appeal. Below that gap, the board may shrug.

Want a worksheet that walks every step without handing a contingency firm 25 to 40% of your savings? The TaxFightBack DIY Appeal Kit builds one in.

Step 6: Check your property record card for factual errors before you run a single comp. If it shows 3 bathrooms and you have 2, or 2,400 square feet when you have 1,950, that error alone can justify a reduction with no comps at all ^[3].

What errors in your assessed value are most common and easiest to fix?

Factual errors are the easiest wins. Assessors process thousands of parcels, and their records carry mistakes more often than homeowners expect.

Common ones: wrong square footage (often because an unfinished basement or garage got counted as finished space), incorrect bedroom or bathroom count, wrong lot size, a phantom pool or second garage on record, and condition ratings that ignore real deferred maintenance or damage ^[2]. Any of these is a clean, factual argument that doesn't require you to debate market value at all.

Valuation errors are subtler. They come from bad comp selection: sales that are too far away, too old, or from a higher market tier. They also come from a CAMA model that misses a real locational penalty, like a house backing to a highway, sitting under a flight path, or wedged next to commercial uses.

Equity errors are their own category. Your assessed value might match the assessor's opinion of market value just fine, yet your neighbors with similar homes carry a lower ratio than you. Many states have uniformity clauses that let you appeal on equity grounds even when your market value estimate is defensible ^[4]. The argument: you're assessed at a higher percentage of market value than comparable properties, which breaks the uniformity requirement.

Georgia's 40% ratio and uniformity rules under O.C.G.A. § 48-5-7 make equity appeals a real path there. Our cherokee county tax assessor, coweta county tax assessor, and madison county tax assessor guides walk the Georgia process at the local level.

How much can your assessed value increase each year?

It depends entirely on your state, and the spread is enormous.

California's Proposition 13 caps assessed value increases at 2% per year for the same owner, no matter what the market does ^[1]. The cap resets to market value on a sale.

Texas caps the appraised value increase for homestead properties at 10% per year under Texas Tax Code § 23.23, however far market values jump ^[5]. That cap doesn't cover non-homestead property.

Georgia lets assessors raise or lower assessed value as the market moves, but owners can pursue a temporary freeze through the arbitration process or appeal each cycle ^[6].

Florida's Save Our Homes cap holds annual increases for homestead properties to 3% or the rate of inflation, whichever is lower, under Florida Statute § 193.155 ^[11].

Plenty of states cap nothing for non-homestead or commercial property. A hot market can drive a single-year assessed value jump of 30 to 50% with no ceiling at all.

What this means for you. If your state has a cap and you've owned for years, your assessed value may sit far below market, your taxes are low, and you probably don't need to appeal. If you bought recently, you likely got reassessed to full purchase price, so your number may be accurate even when it stings. The owners most likely to be overassessed are those in uncapped jurisdictions whose values have slipped since the last assessment, or anyone with real property damage the assessor never saw.

How do you read your assessment notice to spot errors fast?

Your assessment notice has a predictable anatomy. Check four things in the first five minutes.

First, confirm the property description. The notice lists what the assessor thinks you own: square footage, lot size, year built, bedroom and bathroom count, sometimes a condition or quality rating. Match every line against your purchase records, permit records, or a quick walkthrough. Any mismatch is an instant flag.

Second, note the assessment ratio on the notice. Divide your assessed value by it. That gives the assessor's implied market value. Ask the blunt question: could I sell this house for that price in 30 days? If not, that gap is your appeal.

Third, find the appeal deadline. Notices are legally required to state it ^[2]. It typically runs 30 to 90 days from the notice date, and most states offer no do-overs if you miss it.

Fourth, check your exemptions. If you qualify for a homestead, senior, or veteran's exemption and it isn't on the notice, you're overpaying even when the assessed value itself is right. Exemption fixes are often simpler than valuation disputes and don't always need a formal hearing.

Keep that notice. It's the legal starting point for everything that follows.

What is the difference between assessed value and taxable value?

Taxable value is what's left after exemptions come off assessed value. That's the number your tax rate actually hits.

Assessed value of $300,000 with a $50,000 homestead exemption gives you a taxable value of $250,000. The rate applies to $250,000, not $300,000.

Some states stack exemptions. Georgia has a statewide homestead exemption plus county-level and school-district exemptions that add on top of it ^[6]. Texas gives a $40,000 homestead exemption on school district taxes, plus extra exemptions for seniors and disabled veterans ^[5].

When an assessment notice hands you what looks like a brutal tax bill, check whether exemptions are applied before you panic. Homestead exemptions rarely transfer automatically when a home changes hands, so if you bought recently and the prior owner had exemptions, you may need to file for yours separately.

The Lincoln Institute of Land Policy keeps a 50-state database of effective tax rates and exemption structures that helps you see where your state sits nationally ^[8].

How do you know if your assessed value is worth appealing?

Run one quick test before you do anything else.

Take the assessor's implied market value (assessed value divided by your state's ratio) and set it against recent actual sales of similar homes within half a mile, closed in the last twelve months. If the implied value sits more than 10 to 15% above what you can document in those sales, the appeal is probably worth filing.

Then weigh the dollars. A $30,000 reduction in assessed value in a county with a 2% effective rate saves you $600 a year. That's real money, year after year. A $5,000 discrepancy saves about $100 a year. If you're going to spend a weekend pulling records and sitting through a hearing, a $5,000 gap usually isn't worth it, unless your county lets you file online in twenty minutes.

A 2022 analysis by the University of Chicago's Harris School of Public Policy found lower-value homes are overassessed relative to higher-value homes across a majority of studied jurisdictions, so higher-value owners sometimes catch relative relief while lower-value owners pay a higher effective rate ^[9]. Nobody has clean national data on how often appeals succeed. The Indiana Legislative Services Agency, in a 2019 analysis, found roughly 30 to 40% of appealed assessments in Indiana ended in a reduction ^[10]. Bring real evidence and appeals win at a meaningful rate.

For st. louis county personal property tax or bibb county tax assessor situations, local rules on what evidence a hearing will accept change your strategy, so read those jurisdiction guides before you file.

What evidence do you need to challenge your assessed value?

The strongest residential appeal package has three parts.

Comparable sales come first. Three to six closed sales of homes like yours in size, age, condition, style, and location, sold within the last year, ideally within half a mile. Make each comp as close to your home as you can, and note your adjustments for the differences. Pull from the same databases the assessor uses when possible: your county's recorded deed data or the assessor's own comp lookup.

Your property record card comes second, with errors marked. Print it from the assessor's portal, flag every factual mistake in red, and attach proof: your mortgage survey for square footage, permits showing what was or wasn't built, photos of condition problems.

A recent appraisal comes third, if the gap is big. A licensed residential appraisal runs $350 to $600 in most markets and carries real weight at a hearing because a credentialed professional produced it ^[3]. For a discrepancy under $30,000 to $40,000 in assessed value, the cost may not pencil out. For larger gaps, it often does.

What you don't need: an attorney, a contingency-fee firm, or any professional at all for most residential appeals. The TaxFightBack DIY Appeal Kit hands you the same evidence templates and calculation worksheets the paid services run, so you keep 100% of what you save.

Skip what boards ignore. Zillow Zestimates, your purchase price from a different market several years ago, and national inflation statistics that say nothing about your specific house all get waved off.

Frequently asked questions

Is assessed value the same as the price I paid for my home?

No. Assessed value is set by the county assessor using mass appraisal methods and is independent of your purchase price, though many states reset assessed value to purchase price when a sale occurs. In California, Proposition 13 sets assessed value at purchase price and then caps increases at 2% annually. In other states the assessor reassesses on a cycle regardless of sales.

How often is assessed value updated?

It depends on your state. Some states reassess annually, some every two years, some every four to six years. North Carolina reassesses every four to eight years depending on county. Illinois reassesses every four years in most counties, every three years in Cook County. Your assessment notice will identify the tax year; check your assessor's website for the reassessment cycle schedule.

Can my assessed value go down?

Yes, in most states without a strict floor. If market values in your area have declined since the last assessment, you can argue for a lower assessed value in your appeal. States with assessment caps (California, Texas homestead, Florida homestead) typically prevent assessed value from rising past the cap but also allow reductions when market value falls below the capped assessed value.

What is the assessment ratio in my state?

Assessment ratios range from 10% to 100% of market value. Common examples: Texas 100%, Georgia 40% (O.C.G.A. § 48-5-7), Arizona residential 10% (A.R.S. § 42-15001), Illinois non-Cook 33.33% (35 ILCS 200/9-145), California effectively the purchase price under Proposition 13. Your state's department of revenue website publishes the official ratio.

How do I find my property record card?

Visit your county assessor's website and search by address or parcel number. Most counties display a property record card or property detail page showing the assessor's data: square footage, bedroom and bathroom count, year built, lot size, and condition rating. Some smaller counties require a public records request. The record card is your first check for factual errors before you run comps.

What happens to my assessed value when I sell my home?

In most states, a sale triggers a reassessment to the sale price or to fair market value as evidenced by the sale. California resets to purchase price under Proposition 13. Texas reassesses to market value. Georgia reassesses annually regardless of sale. The new assessed value is then subject to whatever exemptions the new owner qualifies for, which must be filed separately in most jurisdictions.

Can I appeal my assessed value every year?

In most states, yes, you can file an appeal every assessment cycle. Texas allows annual protests. Georgia allows annual appeals. Illinois allows annual appeals during the open window in each township's assessment year. The practical question is whether your assessed value changes enough year to year to make filing worthwhile. Some jurisdictions freeze your value during a pending appeal or after a prior settlement.

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

Not automatically. If your local tax rate (mill rate) decreases while your assessed value rises, your bill could stay flat or even fall. Conversely, a stable assessed value combined with a levy increase raises your bill. Your tax bill equals assessed value minus exemptions, times the tax rate. Focus on both the assessed value and the levy when analyzing your bill.

What is the difference between assessed value and appraised value for tax purposes?

Assessed value is the official number the county uses to calculate taxes. Appraised value is an independent estimate of market value produced by a licensed appraiser. For tax purposes, a private appraisal has no automatic legal effect but can serve as powerful evidence in an appeal hearing. An appraisal that documents a lower market value than the assessor's implied value is one of the strongest single pieces of evidence you can submit.

What is the assessment ratio test and how do I use it?

Divide your assessed value by your state's official assessment ratio. The result is the market value the assessor is implying. Compare that to actual recent sales of similar homes. If the implied market value exceeds comparable sales by more than 10 to 15%, you have the basis for a valuation appeal. This ratio test is the same check that state equalization boards use when auditing assessor accuracy.

Can renovations increase my assessed value even if I didn't sell?

Yes. Permitted improvements are reported to the assessor through building permits and trigger a reassessment of the improved value. Adding a bedroom, finishing a basement, or building an addition almost always raises assessed value. Cosmetic upgrades that don't require permits typically do not. Unpermitted work is a gray area: if the assessor discovers it during a field review, they can assess it retroactively in some states.

What if I think my entire neighborhood is overassessed?

You still appeal your own parcel individually; there's no class-action mechanism for most residential appeals. However, if you can show that the median assessment ratio in your neighborhood (assessed value divided by sale price) is systematically higher than the county-wide ratio, that's an equity argument under most state uniformity statutes. Some advocacy organizations have organized neighborhood-wide appeal campaigns where each owner files individually but uses shared comp data.

Do I need a lawyer or appraiser to appeal my assessed value?

For most residential appeals under $50,000 in disputed assessed value, no. The informal hearing process at the assessor's office or local board of review is designed to be accessible to homeowners without professional representation. You need solid comparable sales data, your property record card, and a clear explanation of the discrepancy. A licensed appraisal strengthens the case but costs $350 to $600 and is only cost-effective when the potential annual savings justify it.

What is a mill rate and how does it turn my assessed value into a tax bill?

A mill rate is the tax charged per $1,000 of taxable value. One mill equals $1 per $1,000. If your taxable value is $250,000 and your combined mill rate is 20 mills, your bill is $5,000 (250 times 20). Local governments set the rate each year based on their budget, so the same assessed value can produce different bills in different years or districts.

Sources

1. California State Board of Equalization, Proposition 13 Overview: California's Proposition 13 caps annual assessed value increases at 2% and resets to market value on sale
2. International Association of Assessing Officers (IAAO), Standard on Mass Appraisal of Real Property: Assessment notices must state the assessed value, the basis for assessment, and the appeal deadline; sales comparison, cost, and income approaches are the three accepted valuation methods
3. Appraisal Institute, The Appraisal of Real Estate (14th ed.) overview: Computer-assisted mass appraisal (CAMA) applies statistical models across large property populations; a residential appraisal typically costs $350 to $600
4. Illinois General Assembly, 35 ILCS 200/9-145, Assessment Levels: Illinois sets the residential assessment level at 33.33% of fair market value for non-Cook County properties; uniformity clauses allow equity-based appeals
5. Texas Comptroller of Public Accounts, Texas Tax Code § 23.23 and Homestead Exemption: Texas appraises at 100% of market value; Texas Tax Code § 23.23 caps homestead appraised value increases at 10% per year; homestead exemption is $40,000 on school district taxes
6. Georgia Department of Revenue, Property Tax Division, O.C.G.A. § 48-5-7: Georgia assesses residential property at 40% of fair market value under O.C.G.A. § 48-5-7
7. Arizona Department of Revenue, A.R.S. § 42-15001, Property Classification and Assessment Ratios: Arizona sets the residential assessment ratio at 10% and the commercial ratio at 18% under A.R.S. § 42-15001
8. Lincoln Institute of Land Policy, Significant Features of the Property Tax (50-state database): The Lincoln Institute maintains a 50-state database of effective property tax rates, assessment ratios, and exemption structures
9. University of Chicago Harris School of Public Policy, 'The Regressivity of the Property Tax Assessment Process' (2022): A 2022 University of Chicago Harris School analysis found residential properties in lower-value tiers are overassessed relative to higher-value homes in a majority of studied jurisdictions
10. Indiana Legislative Services Agency, property tax appeals analysis (2019): A 2019 Indiana Legislative Services Agency analysis found roughly 30 to 40% of appealed assessments in Indiana resulted in a reduction
11. Florida Department of Revenue, Florida Statute § 193.155 (Save Our Homes): Florida's Save Our Homes cap limits annual assessed value increases for homestead properties to 3% or the rate of inflation, whichever is lower