Assessed value defined: what it means and why it drives your tax bill

Last updated 2026-07-09

What is assessed value, exactly?

Assessed value is the number your local government puts on your property to figure your property tax. That's the whole definition. Everything else (the ratios, the exemptions, the mill rates) is machinery bolted on top of that one figure.

Your assessor's office sets it, usually once a year or on a fixed reassessment cycle. They're not trying to guess what your house sells for tomorrow. They're applying one legally defined method across every parcel in the county so the tax burden gets split proportionally.

The confusion starts here. Assessed value is not the same as market value, and it's not the same as appraised value either. Those are three separate numbers that people mix up all the time, and the difference matters a lot when you're staring at a tax bill you think is too high.

How is assessed value different from market value and appraised value?

Market value is what a willing buyer pays a willing seller in an arm's-length deal. Appraised value is a licensed appraiser's opinion of that market value. Assessed value is whatever the government says it is, pulled from one of those estimates and then often adjusted by a legal ratio called the assessment ratio or assessment level.

The relationship is simple:

Assessed Value = Market Value × Assessment Ratio

If your state uses a 100% ratio, assessed value should equal market value. California's Proposition 13 caps assessed value at the purchase price plus a maximum 2% annual increase, so longtime owners often carry assessed values far below what their homes would sell for ^[1]. In Cook County, Illinois, residential property is assessed at 10% of market value under state law, so a $400,000 home shows an assessed value of $40,000 ^[2]. Neither number is wrong. They're playing by different local rules.

Appraised value shows up when you refinance or sell. A bank appraisal and a tax assessment usually differ because they use different data for different reasons. The bank appraiser protects a lender's collateral. The assessor splits a tax burden. Don't assume your tax assessment tracks your appraisal, and don't assume either one is "correct" in any universal sense.

Term	Who produces it	Purpose	Legal basis
Market value	Buyers and sellers collectively	Price discovery	None, it's a market outcome
Appraised value	Licensed appraiser	Lending, estate, insurance	State licensing law
Assessed value	County or local assessor	Property tax calculation	State statute
Taxable value	Assessor after exemptions	Actual tax base	State statute + exemption law

What is an assessment ratio and why does it vary by state?

The assessment ratio is the percentage of market value your assessor is supposed to use when setting assessed value. It exists because state legislatures decided, for a mix of political and policy reasons, that taxing 100% of market value is either a headache to administer or a hard sell to voters.

Every state sets its own ratio by statute or constitution. Some use one statewide ratio. Others let counties or towns pick their own. A handful apply different ratios to different property classes, so commercial real estate gets assessed at a higher ratio than a house down the block.

Here's the practical effect. Two identical houses on opposite sides of a state line can carry wildly different assessed values even if they'd sell for the same price. That's not a mistake. That's the system doing exactly what it was built to do.

The International Association of Assessing Officers (IAAO) recommends that assessed values for a given class of property stay within a coefficient of dispersion (COD) of 15% or less, meaning assessments should land reasonably close to the ratio on average ^[3]. When that uniformity slips, low-value homes in a neighborhood tend to get over-assessed relative to high-value ones, a pattern researchers have documented for decades.

A 2021 study in the Journal of Housing Economics found the lowest-value homes in Chicago were assessed at effective rates roughly 3.4 times higher than the highest-value homes, driven partly by how mass appraisal models handle data-sparse lower-value neighborhoods ^[4].

How do assessors actually calculate assessed value?

Most offices use mass appraisal. That means the assessor runs statistical models to value thousands of properties at once instead of walking through each one every year. The three main approaches are the same ones a fee appraiser uses, just run at scale.

The sales comparison approach looks at recent arm's-length sales of comparable properties (comps). The cost approach estimates what it would cost to rebuild the structure, knocks off depreciation for age and condition, then adds land value. The income approach applies to income-producing property and turns expected rent into a value estimate.

For single-family homes, sales comparison wins in most places. The model adjusts for square footage, bedroom count, lot size, age, condition, and location. If the model is well-calibrated and the market is steady, it works fine. If the market is moving fast (like it did from 2020 through 2022) or local sales are thin, errors pile up.

Some things the model simply can't see: deferred maintenance the owner knows about but never disclosed, a wet basement, a foundation crack, a busy road or a cell tower next door, and anything changed since the last physical inspection. Those blind spots are exactly where appeals win, because you hold evidence the model never had.

The assessor doesn't have to inspect your property in person every year. In a lot of counties, on-site inspections happen on a set cycle, sometimes every five to ten years, or when someone pulls a building permit. Between visits, the model revalues you off neighborhood sales data. That data may or may not reflect what's actually going on with your house ^[5].

How does assessed value actually turn into a tax bill?

The path from assessed value to tax bill runs through a few steps most homeowners never see.

First, exemptions come off. A homestead exemption might cut your assessed value by a flat dollar amount (say $25,000) or a percentage before any tax rate applies. Senior, disability, veteran, and agricultural exemptions work the same way. What's left is your taxable value.

Second, taxable value gets multiplied by the mill rate (also called the millage rate). One mill equals $1 of tax per $1,000 of taxable value. A mill rate of 20 on a $200,000 taxable value produces a $4,000 annual bill. Your local taxing bodies set those rates: the county, the school district, the town, and any special districts.

The full chain looks like this:

Market Value × Assessment Ratio = Assessed Value Assessed Value minus Exemptions = Taxable Value Taxable Value × Mill Rate / 1,000 = Annual Tax Bill

Here's why the fight matters even when the annual dollars look small. A $20,000 over-assessment at a combined mill rate of 25 costs you $500 a year. Leave it unchallenged for five years and that's $2,500 gone. The error multiplies through every step after it.

For a county-level look at how this lands on real bills, the Los Angeles County property tax and Maricopa property tax pages walk through each jurisdiction's rate structure and exemptions.

What is equalization and why should you care?

Equalization is a state agency's check on whether each county is actually assessing at the legally required ratio. Say County A assesses at 85% of market value and County B assesses at 95%. Owners in County B pay a higher effective rate even when the stated mill rates match exactly.

To close that gap, the state applies equalization factors (also called multipliers) to county-level assessed values, pulling them to the statutory level. In Illinois, the Department of Revenue publishes an equalization factor for each county every year, and the Cook County figure is prominent enough that people just call it the "state equalization factor" ^[2].

Why does this land on you? The factor gets applied to your assessed value before your tax rate runs. If your county has a multiplier above 1.0, your real tax base is higher than the notice suggests. If the factor sits below 1.0, you catch a break. Either way, your appeal should target the assessed value before the multiplier hits, which is the number your assessment notice shows.

For homeowners in Cook County, the equalization layer hits hard. Cook's multiplier has historically run from roughly 2.6 to 3.0, so any assessment error gets multiplied by that factor before the tax rate even starts.

Why might my assessed value be wrong?

Assessed values are wrong more often than most homeowners think. The reasons are mostly systemic, not sneaky.

Mass appraisal leans on recent comparable sales. When sales are thin (rural areas, odd property types) or when prices swing fast (a rapid run-up or a sudden drop), the models fall behind reality. Properties that changed condition since the last inspection, properties with unique negative features the model can't see, and properties in neighborhoods where the adjustment factors are poorly tuned all carry higher error risk.

The IAAO's standards say a well-run office should hit a median assessment level within 10% of the target ratio and a COD under 15% ^[3]. Plenty of jurisdictions miss those marks in a given year. And even a "good" COD of 12% means a lot of individual homes are meaningfully off.

Common reasons your assessed value runs too high:

• Recent sales of comparable properties support a lower market value
• Your property has physical problems (condition, functional obsolescence) the assessment ignores
• The assessor's data file has errors (wrong square footage, wrong bedroom count, wrong construction quality grade)
• You're in a neighborhood where values fell faster than the model updated
• A neighboring county sale got used as a comp but the market there differs materially

Start with the assessor's property card. Errors in the basic data (square footage, lot size, bathroom count) are surprisingly common, and they get fixed fast, often without a formal appeal.

How do assessment ratios compare across major states?

There's no federal standard for how states set assessment ratios, so the range is huge. The table below shows the nominal statutory ratios for residential property in a handful of states. Keep in mind that the effective ratio (what assessors actually hit on average) often differs from the statutory target.

State	Statutory assessment ratio (residential)	Notes
California	Purchase price + max 2%/yr increase	Prop 13; no percentage of market value [1]
Illinois (Cook County)	10% of market value	Equalization multiplier applied on top [2]
Texas	100% of market value	Homestead cap limits annual increase to 10% [6]
New York	Varies by municipality	Some localities use 100%, others much lower [7]
Florida	100% (just value)	Save Our Homes cap limits assessed value increase to 3%/yr [8]
Georgia	40% of fair market value	County boards of equalization handle appeals [9]
Arizona	10% of full cash value (residential)	Different ratio for other classes [10]
Massachusetts	100% of fair cash value	Triennial review required [11]

For Georgia examples, the Gwinnett County tax assessor and Cherokee County tax assessor pages show how the 40% ratio plays out across metro Atlanta counties.

For Arizona, the Maricopa property tax page covers how the 10% limited property value system works in Maricopa County specifically.

Can I lower my assessed value, and what's the realistic way to do it?

Yes, and the numbers on your side are better than most people expect. Most assessors' offices report that 30% to 60% of formal appeals produce some reduction, depending on the jurisdiction and property type. Nobody has clean national data on this. The closest systematic evidence comes from individual county disclosure reports and academic studies of specific markets, so treat any single figure as a range, not gospel.

The realistic path has three steps.

Step one: get your property record card from the assessor's website or office and check every field. Square footage, year built, bedroom and bathroom count, lot size, and quality grade all feed the model. If any of it is wrong, you have a factual correction claim that usually clears at the informal review level, no hearing needed.

Step two: pull recent sales of comparable properties. Most county assessors post sales data online. You want arm's-length sales (not foreclosures, not estate sales, not deals between relatives) from the past six to twelve months, within a reasonable radius, with similar characteristics. If three comparable sales support a market value 10% or 15% below what the assessor used, you have a real sales-comparison argument.

Step three: file before the deadline. This is where most homeowners lose before they've started. Deadlines are hard and unforgiving, usually 30 to 90 days after the notice is mailed, though the exact window shifts by state and county. Miss it and you wait a full year.

If you want a structured way to gather comps, organize your evidence, and draft the actual appeal, TaxFightBack's DIY appeal kit walks the whole process without taking a cut of your savings.

For deadline and process detail by market, the Bexar County tax assessor, San Diego property tax, and Lake County property tax pages cover those places in depth.

What exemptions reduce assessed value (or taxable value) and how do I claim them?

Exemptions are where a lot of homeowners leave cash on the table, because most states don't apply every exemption you qualify for automatically. You often have to apply once, sometimes every year.

The homestead exemption is the common one. It cuts either assessed value or taxable value by a flat dollar amount or a percentage for your primary residence. Texas offers a $100,000 homestead exemption from school district taxes for most homeowners as of 2023 ^[6]. Florida's homestead exemption removes the first $25,000 of assessed value from all taxes and another $25,000 from non-school taxes ^[8].

Other big categories:

• Senior citizen exemptions (age and often income-tested)
• Disability exemptions (sometimes automatic for certain rated disabilities)
• Veteran and surviving spouse exemptions (they vary enormously by state and branch)
• Agricultural or greenbelt classifications (much lower assessed value for qualifying rural land)
• Homestead assessment caps (limits on annual increases, like Florida's Save Our Homes ^[8] or Texas's 10% homestead cap ^[6])

Missing an exemption you qualify for is just overpaying by another name. The fix is usually simple: file the application, provide documentation, and in most states the exemption applies going forward. Some states allow retroactive claims for a limited lookback period.

For states where the exemption system needs its own lookup, the Madison County tax assessor and Bibb County tax assessor pages include local exemption detail.

What should I do immediately after receiving an assessment notice?

Four things, in order.

Write down your appeal deadline first. Don't assume you have time to spare. In Texas, the deadline to protest is May 15 or 30 days after the notice is delivered, whichever is later ^[6]. In California, the window for a formal application to the Assessment Appeals Board runs July 2 through November 30 in most counties ^[1]. In Georgia, it's 45 days from the date on the notice ^[9]. These windows are statute, not suggestion.

Second, pull your property record card. It's usually online through your county assessor's site. Check the physical description against what you know is true. One wrong data point can inflate your assessed value by tens of thousands of dollars.

Third, check recent comparable sales. Look at what similar homes in your neighborhood actually sold for in the six to twelve months before January 1 of the tax year (most states use January 1 as the valuation date). Your county assessor's sales database is a solid starting point, and most are public.

Fourth, decide whether to file before the deadline. You don't have to be sure you'll win. Filing keeps your right alive. Not filing throws it away. A residential appeal costs zero or a modest flat fee in most places (often $15 to $50). Missing the deadline costs you another year of overpaying.

The TaxFightBack DIY appeal kit gives you a checklist for this exact sequence, plus comp-pull worksheets and a pre-filled appeal letter template. No contingency fee, so you keep every dollar of the reduction.

What does assessed value mean for refinancing, buying, or selling?

For taxes, assessed value is the only number that matters. For everything else, it barely registers.

Mortgage lenders don't use assessed value to decide how much to lend. They require a licensed appraisal. The appraisal can come in above or below the assessed value, and neither one controls the other.

When you're buying, a high assessed value relative to purchase price can mean two different things. It can signal you're paying below what the assessor thinks the property is worth (fine for you), or it can flag that the prior owner's assessment carried a protective cap that resets when you close. California's Prop 13 is the classic case: a house assessed at $200,000 because it was bought in 1985 gets reassessed to purchase price when it sells in 2025 for $1,200,000, which hands the new buyer a dramatically higher tax bill ^[1].

When you're selling, a low assessed value generally doesn't hurt you. Buyers and their agents look at market comps, not the tax card. A dramatically low number might just prompt a buyer to ask whether there's a catch.

Using assessed value as a rough stand-in for market value is risky. The gap between the two can be enormous depending on how long it's been since the last reassessment and whether the jurisdiction uses full-value assessment. In places with long reassessment cycles, assessed values can be decades behind market prices.

Frequently asked questions

Is assessed value the same as market value?

No. Market value is what your property would sell for between a willing buyer and seller. Assessed value is what the government assigns for tax purposes, which is often a percentage of market value set by state law, called the assessment ratio. In Illinois's Cook County, for example, residential assessed value is 10% of market value by statute. In Texas, assessed value is meant to equal 100% of market value.

What percentage of market value is assessed value?

It depends entirely on the state. Ratios range from 10% (Cook County, Illinois) to 100% (Texas, Massachusetts). Georgia assesses residential property at 40% of fair market value. Arizona uses 10% for residential. California uses purchase price plus a maximum 2% annual increase under Proposition 13. There is no national standard. Always check your state's specific statute.

How do I find my property's assessed value?

Your annual assessment notice is the primary source. Most county assessor offices also publish assessed values online through a searchable property database. Search your county name plus 'assessor property search' or 'parcel lookup.' You can also call or visit the assessor's office directly. The number you want is on the notice and in the online record, usually labeled 'assessed value' or 'assessed valuation.'

Can my assessed value go down?

Yes. If market values in your area decline and the assessor's model updates to reflect that, assessed values can fall. You can also trigger a reduction by filing a successful appeal. Some states have assessment caps that prevent increases but don't prevent decreases. Florida's Save Our Homes cap limits annual increases to 3% but has no floor, so assessed values can drop when market values fall.

What is taxable value versus assessed value?

Assessed value is the assessor's estimate of your property's value (at the applicable ratio). Taxable value is what's left after you subtract any exemptions you qualify for, like a homestead exemption or senior exemption. Your tax bill is calculated on taxable value, not assessed value. The two are equal only if you have no exemptions. Always check both numbers on your tax notice.

How often is assessed value updated?

It varies by jurisdiction. Some states reassess every year (Texas, California on purchase). Others reassess on a multi-year cycle: every three years in Massachusetts, every four years in some Georgia counties, or on irregular schedules elsewhere. Many offices use annual statistical updates between full reappraisals, adjusting values based on sales data without physically inspecting properties.

What happens to my assessed value when I buy a house?

In most states, a sale triggers a reassessment to the purchase price or close to it. In California, Prop 13 means your assessed value resets to your purchase price and can only increase up to 2% per year going forward. In Florida, the Save Our Homes cap (3% annual increase limit) resets at sale as well. In Texas, the assessed value is supposed to reflect market value regardless of sale.

Does a high assessed value mean I'm being overtaxed?

Not automatically, but it's a red flag worth investigating. High assessed value relative to what your home would actually sell for is the core condition for a successful appeal. Check recent sales of comparable homes. If three or four similar nearby properties sold for materially less than what your assessed value implies as market value (after adjusting for the assessment ratio), you likely have an over-assessment you can challenge.

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

The assessment ratio is the fraction of market value that the assessor is legally required to use when setting assessed value. It's set by state statute or constitutional provision. You can find it by searching your state's department of revenue or department of taxation website, or by looking up your state's property tax code. The IAAO also publishes a periodic summary of state assessment ratios.

Can I appeal my assessed value myself without a lawyer or contingency firm?

Yes, and in most jurisdictions the informal review or formal appeal process is designed to be accessible to homeowners without representation. You need your assessment notice, your property record card, and two to five comparable recent sales. The filing fee is typically zero to $50 for residential property. A contingency firm typically keeps 30% to 50% of the first year's tax savings as its fee, which you keep entirely if you file yourself.

How long does an assessed value appeal take?

An informal review with the assessor's office can resolve in a few weeks. A formal hearing before a board of equalization or review typically takes two to six months from filing, depending on the jurisdiction's backlog. In high-volume counties like Cook County, Illinois, formal appeals can take longer. Most decisions are issued within the same tax year if you file early in the appeal window.

What is the equalization factor and how does it affect my taxes?

An equalization factor (or multiplier) is a number applied by the state to a county's assessed values to bring them closer to the statutory assessment level. If a county is assessing below its required ratio, the state applies a factor above 1.0 to adjust upward. Illinois is the most well-known example: Cook County's state equalization factor is published annually and has historically been in the 2.6 to 3.0 range, multiplying the county's assessed values before tax rates are applied.

Does homestead exemption lower assessed value or taxable value?

It depends on the state. Some exemptions directly reduce assessed value before the tax rate is applied. Others reduce taxable value (assessed value minus exemptions). The practical effect is similar: your tax bill drops. In Texas, the homestead exemption reduces taxable value. In Georgia, the basic homestead exemption reduces assessed value by a flat $2,000 at the county level, with additional local options available.

Is assessed value public record?

Yes, in all 50 states. Property assessment records are public by law. You can look up the assessed value, property record card, ownership history, and often recent sales data through your county assessor's online portal. Some jurisdictions charge a small fee for printed records, but electronic access is free in the vast majority of counties. This public access is what makes DIY appeals feasible.

Sources

1. California State Board of Equalization, Proposition 13 overview: California's Prop 13 caps assessed value at the purchase price plus a maximum 2% annual increase and resets to purchase price at sale
2. Cook County Assessor's Office, assessment levels and equalization: Cook County residential property is assessed at 10% of market value and the state equalization factor is applied on top of that
3. International Association of Assessing Officers (IAAO), Standard on Ratio Studies: IAAO recommends a coefficient of dispersion (COD) no greater than 15% for residential assessments, indicating acceptable uniformity
4. Avenancio-León & Howard, 'The Assessment Gap: Racial Inequalities in Property Taxation,' Journal of Housing Economics (2021): A 2021 study found the lowest-value homes in Chicago were assessed at effective rates roughly 3.4 times higher than highest-value homes
5. Lincoln Institute of Land Policy, Significant Features of the Property Tax: Mass appraisal models update valuations between physical inspections using neighborhood sales data, creating gaps for properties with unique issues
6. Texas Comptroller of Public Accounts, Property Tax Exemptions: Texas offers a $100,000 homestead exemption from school district taxes for most homeowners (as of 2023) and caps annual homestead value increases at 10%; protest deadline is May 15 or 30 days after notice
7. New York State Department of Taxation and Finance, Property Tax Overview: New York assessment ratios vary by municipality, with some localities using 100% of market value and others using a fraction
8. Florida Department of Revenue, Property Tax Oversight, Save Our Homes and Homestead Exemption: Florida's homestead exemption removes the first $25,000 of assessed value from all taxes and another $25,000 from non-school taxes; Save Our Homes caps annual increases at 3% and resets at sale
9. Georgia Department of Revenue, Property Tax Overview: Georgia assesses residential property at 40% of fair market value; the appeal deadline is 45 days from the date of the assessment notice
10. Arizona Department of Revenue, Property Tax Overview: Arizona assesses residential property at 10% of full cash value; different ratios apply to other property classes
11. Massachusetts Department of Revenue, Division of Local Services, Property Tax Assessment: Massachusetts requires that property be assessed at 100% of fair cash value and mandates triennial full revaluation