Tax assessment vs. appraisal value: what's actually different and why it matters for your tax bill

Last updated 2026-07-09

What is the difference between a tax assessment and an appraisal?

A tax assessment is a government act. An appraisal is a private opinion. Your county or municipal assessor's office assigns your property a value, usually once a year or on a set cycle, and that number flows straight into your tax bill. An appraisal is a licensed professional's opinion of what your home would sell for if it hit the market today.

Those two numbers answer to different bosses. Assessed value exists to split the tax burden across every property in a jurisdiction. Appraised (or market) value exists to protect a buyer, seller, or lender in a deal. They can land close together. They can also sit tens of thousands of dollars apart, and that gap is rarely an accident.

The link between the two is a number called the assessment ratio (sometimes an assessment level or equalization rate). A ratio of 100% means the assessor is supposed to value your property at full market value. A ratio of 80% means 80% of market value. A ratio of 10%, which Alabama uses for residential property, means your assessed value is one-tenth of what you could sell for ^[1].

Here is the formula the whole system runs on:

Assessed Value = Market Value × Assessment Ratio

So a home worth $400,000 in a county with an 80% ratio should carry a $320,000 assessed value. The tax rate (millage) then applies to that $320,000, not the full $400,000. Every legitimate property tax appeal starts by understanding this chain.

How does the assessor determine your property's value?

Most residential valuations use one of three approaches, or a blend. Almost none of them involve a licensed appraiser walking through your living room.

The sales comparison approach lines your home up against recent sales of similar properties nearby. It's the same logic a real estate agent uses to price a listing, run in bulk across thousands of parcels. This is the main method for single-family homes.

The cost approach estimates what it would cost to rebuild your structure from scratch, subtracts depreciation, then adds land value. Assessors reach for it on new construction, unusual properties, or places where comparable sales are thin.

The income approach turns a property's net operating income into a value estimate. It applies to commercial and rental property, not your primary residence.

Mass appraisal models process entire counties at once using statistics, not inspections. The International Association of Assessing Officers publishes standards for how accurate those models should be: a median assessment-to-sale ratio between 90% and 110% of market value, with a coefficient of dispersion (a measure of how scattered the ratios are) of 15% or less for residential property ^[2]. Plenty of jurisdictions miss that target. That's exactly why appeals succeed.

A private appraisal is a different animal. A licensed appraiser inspects your home, picks three to five comparable sales, makes manual adjustments for the differences, and signs a report that carries professional liability. That report runs $300 to $600 for a standard residential property, more in high-cost markets ^[3]. It carries more weight per page than any mass model, and it's often the single strongest piece of evidence in a tax appeal.

How do assessment ratios vary by state?

There is no national standard, which is where most homeowners get lost. Every state writes its own rules, and some hand the decision down to individual counties.

State	Residential Assessment Ratio	Notes
California	100% of purchase price (then limited)	Prop 13 caps annual increases at 2% [4]
Texas	100% of market value	Homestead exemption and 10% cap on taxable value apply [5]
Alabama	10% of market value	One of the lowest ratios in the country [1]
New York	Varies by county	NYC uses 6% for Class 1 residential; upstate counties vary widely [6]
Illinois (Cook County)	10% of market value for residential	Other counties: 33.33% [7]
Colorado	6.95% of actual value (2023)	Legislature has changed this ratio several times recently
Maryland	100% (phased in over 3 years)	Increases capped at 10% per year for homestead properties [8]
Florida	100%	Save Our Homes cap limits increases to 3% or CPI, whichever is less [9]

A few patterns stand out. Southern states tend to use low ratios, which makes assessed values look small even when effective tax rates are moderate. California and Florida cap how fast assessed values can grow, so long-term owners often pay tax on a number far below current market value. New buyers in those states sometimes get a nasty surprise when the cap resets at purchase.

Own property in the DC suburbs? The Montgomery County property tax and Loudoun County property tax systems both assess at 100% of estimated fair market value. In theory your assessed value and market value should match. In a fast-moving market, they often don't.

Why is my assessed value higher (or lower) than what my home would sell for?

Both directions happen, and each means something different for your wallet.

Assessed value higher than market value means you're overpaying. This is the setup that calls for an appeal. It happens most when prices in your neighborhood have fallen since the last assessment cycle, or when the assessor's model got your property wrong: bad square footage, an extra bedroom that doesn't exist, a finished basement that's actually a dirt crawlspace.

Assessed value lower than market value means you're getting a relative break, and you should probably keep quiet about it. This is common in states with assessment caps or long reassessment cycles. A California owner who bought in 1995 might carry a $200,000 assessed value on a home worth $1.2 million today, purely because Proposition 13 caps growth at 2% a year ^[4].

There's a third case worth knowing. Your assessed value can be roughly right relative to market value while your neighbors' assessments run systematically lower. That's an equity or uniformity argument, and it's a valid basis for appeal in most states even when your own number is defensible. The principle traces to the Fourteenth Amendment's equal protection clause, and every state tax code has its own version. You don't have to prove your value is wrong. You just have to prove you're assessed at a higher ratio than comparable homes.

The gap between assessed and market values is not random. A 2020 study by the University of Chicago's Harris School found assessment regressivity in nearly every major county it examined, meaning owners of cheaper homes are taxed at higher ratios than owners of expensive ones and carry more than their share of the burden ^[3].

For how this plays out in one big urban county, the DeKalb County tax assessor page walks through Georgia's 40% assessment ratio in practice.

Does a bank appraisal equal my tax-assessed value?

No, and they aren't supposed to. A mortgage appraisal is a licensed appraiser's opinion of market value at one point in time, usually during a purchase or refinance. A tax assessment is a government estimate, often lagged a year or more, sometimes applying a ratio below 100%, and built on mass modeling rather than an individual inspection.

In practice, bank appraisals often come in higher than assessed values, especially in rising markets where the assessor hasn't caught up. They can come in lower too, in declining markets or when the assessor's model has systematic errors.

Here's the part that matters: your bank appraisal is legitimate evidence in a tax appeal. If a licensed appraiser valued your home at $350,000 six months ago and your county just assessed it at $420,000, that appraisal is a concrete, professionally backed rebuttal. Many assessment offices accept it without making you commission a fresh one. Bring the full report, not the cover page.

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

Market value has a specific legal definition in most places. The Uniform Standards of Professional Appraisal Practice define it as "the most probable price a property should bring in a competitive and open market under all conditions requisite to a fair sale" ^[10]. Note the word "probable." Not maximum, not what someone once offered at a wine-fueled open house.

Assessed value starts from that same market value concept, then runs it through the assessment ratio and, in many states, caps and exemptions. The chain looks like this:

Market Value → × Assessment Ratio → Assessed Value → minus Exemptions → Taxable Value → × Tax Rate (Millage) → Tax Bill

Every step can help you or hurt you. A homestead exemption might strip $50,000 off your assessed value before the rate applies. A senior freeze might lock your taxable value at a prior year regardless of the market. None of that touches market value. It just changes how much of that value gets taxed.

So when someone asks what separates a tax assessment from market value, the honest answer is short: market value is an estimate of what your property would trade for, and assessed value is the number the government assigns for tax purposes, which may be a fraction of market value, subject to political caps, and lagged by time.

For how these numbers feed the final bill, see property tax explained: how it's set and how to appeal it.

How do I find my current assessed value and check if it's accurate?

Start with your local assessor's website. Almost every county now runs a public records portal where you look up your parcel by address. You'll usually find your assessed value, the assessment ratio if the county publishes it, comparable property data, and sometimes the field notes from your last physical inspection.

The property tax lookup tool helps you find the right county portal fast. Once you have your assessed value, run a quick sanity check:

1. Find three to five homes that sold within the last six months, within a half-mile of yours, similar in size, age, and condition. Your county's parcel search often shows recent sales. Zillow, Redfin, and the county recorder all work.

2. Reverse the ratio to see what market value the assessor is implying. If your assessed value is $240,000 and your county assesses at 80% of market value, the implied market value is $300,000. Does that match what similar homes actually sold for?

3. Check the property characteristics on your assessment record. Assessors often carry wrong data: square footage pulled from permits that were never updated, phantom bathrooms, finished space that's really a crawlspace. Data errors are among the easiest grounds for a win.

Texas works differently. The appraisal district, not a county assessor, handles valuations. The Bexar County property taxes and Denton County property tax pages explain how Texas protests run, including the May 15 deadline that applies in most counties ^[5].

Nevada adds its own twist. The Clark County Assessor assesses at 35% of taxable value, which is itself already a depreciated figure, so the chain from market price to tax bill gets murky fast. The Clark County property tax guide breaks it down.

Can I use a home sale price as evidence that my assessed value is too high?

Yes, and it's often the cleanest evidence you can bring. If you bought recently at arm's length (not from a relative, not in foreclosure, not under duress), that sale price is the market's own verdict on value at that moment. Most state appeal boards treat a recent arm's-length sale as strong evidence.

The closer the sale sits to the assessment date, the more it counts. Most jurisdictions use a specific "valuation date" or "lien date," usually January 1 of the tax year. Sales within six months of that date carry real weight. Sales from two years back are weaker but still admissible as support.

The argument writes itself: "I paid $380,000 for this house on October 15, in an open market transaction with no relationship to the seller. The county assessed it at $430,000 as of January 1. The assessment exceeds my purchase price by $50,000 with no material improvement to the property."

Bring your Closing Disclosure or HUD-1 (the settlement statement from closing), more than the deed. The settlement statement shows the actual sale price and confirms it was a cash or mortgaged purchase at full value, which shuts down the "related party" objection assessors sometimes throw at you.

Philadelphia homeowners have their own quirks. The Philadelphia property tax system weighs recent sales differently in appeals before the Board of Revision of Taxes. Check the local rules before you file.

What's the assessed value ratio in my state, and how do I find it?

Your state department of revenue or taxation publishes it. Search terms that work: your state name plus "assessment ratio," or "equalization rate," or "assessment level."

Two free resources cover the whole country. The IAAO runs an annual survey of assessment administration, and the Lincoln Institute of Land Policy keeps a "Significant Features of the Property Tax" database with ratios and rates by state ^[11].

Many states use different ratios for different property classes. Commercial usually carries a higher ratio than residential. Farmland usually carries a lower one. Illinois takes it to an extreme: in Cook County, residential is assessed at 10%, commercial at 25%, and industrial at 25%, all as percentages of the same market value ^[7].

Once you know your ratio, you can benchmark yourself. If the state says residential should sit at 80% of market value and your implied ratio (assessed value divided by what similar homes sold for) is 95%, you've got a clean equity argument.

The values assessment and property assessment value pages go deeper on running that ratio math for specific states.

How does the difference between assessed and appraised value affect a property tax appeal?

The gap is the appeal. If assessed value equals market value, and market value is estimated correctly, there's nothing to fight. The opening exists because one of two things went wrong: the assessor overestimated market value, or the assessor applied the ratio unevenly.

When you appeal, you argue one or both. The two common shapes:

Market value argument: "The assessor says my home is worth $450,000. Here are three comparable sales from the last four months showing homes like mine sold between $370,000 and $395,000. My assessed value should be no more than $385,000."

Uniformity argument: "The assessor values my home at 105% of market value based on those same sales. The IAAO standard is 90 to 110%, but the median ratio in my neighborhood is 88%. I'm assessed higher than my neighbors, which violates my state's uniformity clause."

A private appraisal props up the first argument. Comparable assessment data from public records props up the second. Together they make a strong file.

Plenty of homeowners skip the appraisal and win using only comparable sales and the county's own parcel data. For a first shot at an informal hearing or a board of equalization review, that's often enough. Save the $400 appraisal for a formal hearing or small claims tax court if the informal review goes nowhere.

The TaxFightBack DIY appeal kit walks through building both arguments from public records, without handing a contingency firm 25 to 40% of your refund.

What are the deadlines to appeal a tax assessment?

Missing the deadline is the one unrecoverable mistake in a property tax appeal. Every other error can be fixed. A blown deadline kills your case for the entire year.

Deadlines swing wildly by state and sometimes by county. The range runs from 30 days after the notice is mailed (some California counties) to six months after the assessment date (some New York counties). A few states use calendar-year deadlines. Illinois boards of review, for example, tend to meet in the fall no matter when your notice arrived.

The anchor is almost always the assessment notice date, not the tax bill date. Your assessment notice and your tax bill are different documents. The notice is what starts the clock.

Some general patterns:

• Texas: May 15 or 30 days after the notice, whichever is later ^[5]
• California: September 15 in most counties, or 60 days from the notice, whichever is later ^[12]
• Florida: 25 days from the mailing of the notice of proposed property taxes ^[9]
• New York: Varies by assessing unit; typically filed in the spring for the following tax year ^[6]
• Illinois: Typically 30 days from the date your assessment was published ^[7]

The property tax records page helps you track down your notice date if you missed it or aren't sure when it went out.

One honest hedge: these deadlines shift when legislatures act, and some counties run local rules that break from the state baseline. Verify against your county assessor's website or your state department of revenue's current guidance before filing.

Is a higher appraised value always bad for you as a homeowner?

For taxes, usually yes. For your net worth, your equity, and your ability to borrow, a higher market value is good news. The tension only exists because your tax bill rides on assessed value, which tracks market value.

A few situations flip it. If you're refinancing and your lender needs the appraisal above a certain number to hit the loan-to-value ratio, a strong market value is what you want. If you're selling, a higher market value is more money in your pocket. No mystery there.

The catch is that assessed value and market value don't move at the same speed. In a fast-rising market, assessed values sometimes trail market values by a year or two, handing owners a temporary tax break. When prices fall, many assessors are slow to drop assessed values, leaving homeowners overpaying through the downturn.

Orange County, California shows the pattern well. OC property tax assessments can lag rapidly rising prices, then linger too long after a correction. California's Proposition 8 allows a temporary reduction when market value drops below assessed value, but you have to ask. It does not happen on its own ^[4].

So celebrate a high appraisal on the day you sell. But if market values have dropped and your assessment hasn't followed, filing for a reduction is both legal and reasonable. That's the whole point of the appeal process.

Frequently asked questions

Is assessed value the same as market value?

No. Market value is what your home would sell for in an open transaction. Assessed value is the number your local government assigns for tax purposes, often a percentage of market value set by a state assessment ratio. In Alabama, assessed value is only 10% of market value. In Texas and most Virginia counties, assessed value is meant to equal 100% of market value, though in practice it often doesn't.

Why is my assessed value so much lower than what my home is worth?

Two main reasons. Your state may use an assessment ratio below 100%, so the law deliberately sets assessed values at a fraction of market value. Or you live in a state with an assessment cap (like California's Proposition 13) that limits how fast assessed values can rise. Both cut your tax bill relative to market value, so this is usually a good spot to be in, unless the market has since dropped and your assessment now looks high by comparison.

Can my assessed value be higher than my home's market value?

Yes, and this is the scenario that justifies an appeal. It happens most when prices have fallen since the last assessment cycle, or when the assessor's model got your property's characteristics wrong. If you can show with recent comparable sales that the assessor's implied market value beats what similar homes actually sold for, you have a strong case for a reduction.

Does a bank appraisal affect my property taxes?

Not automatically. Your mortgage lender's appraisal isn't reported to the tax assessor and doesn't trigger a reassessment. But you can use a recent bank appraisal as evidence in a tax appeal if it shows a market value below the assessor's implied value. Bring the full appraisal report to the hearing, not the summary page.

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

An assessment ratio is the percentage of market value at which your county is supposed to assess property. Ratios run from 10% in some states to 100% in others. Find yours on your state department of revenue's website, or search your state name plus "assessment ratio" or "equalization rate." The Lincoln Institute of Land Policy's property tax database also covers all 50 states.

How do I know if my property tax assessment is accurate?

Pull your assessment record from the county assessor's website and check the property characteristics listed: square footage, bedroom count, finished area. Errors are common and easy to prove. Then compare the assessor's implied market value (assessed value divided by your state's ratio) against recent sales of similar homes nearby. If the implied value runs more than 5 to 10% above comparable sales, you probably have grounds to appeal.

What evidence do I need to lower my assessed value?

The strongest evidence is a recent, arm's-length sale of your own home. If you don't have that, gather three to five comparable sales from the last six months of similar homes within a half-mile. A licensed appraisal report is stronger still and costs $300 to $600, but many homeowners win informal appeals using only public comparable sales and assessor records. A property record error, like wrong square footage, can be enough on its own.

Does a higher home sale price in my neighborhood raise my assessed value?

Possibly, but not right away in most states. Assessors update on cycles that range from annual to every few years. In California, your assessed value only rises when your property sells or you add improvements, regardless of what neighbors' homes fetch, thanks to Proposition 13. In most other states, rising neighborhood sales eventually push your assessed value up at the next reassessment.

Is the Zillow estimate (Zestimate) useful for a property tax appeal?

Only as a rough sanity check. Zillow's Zestimate is an automated valuation model with a national median error rate around 2 to 3% for on-market homes and higher for off-market ones. Assessment boards don't accept it as evidence and most will wave it off if you raise it. Use actual recorded sale prices from comparable properties, or a licensed appraisal report. The county's own parcel search often shows recent sales free.

How often do property tax assessments change?

It depends on your state. Annual reassessments happen in Texas, California (on sale), and many others. Biennial cycles are common in Maryland and parts of the Midwest. Indiana and Kentucky use four-year cycles, and some rural jurisdictions run longer. Your assessment can also change mid-cycle if you pull a permit for major construction or the assessor's office flags your property for an interim review.

What is the difference between taxable value and assessed value?

Assessed value is what the assessor assigns. Taxable value is what's left after exemptions come off. A homestead exemption might strip $25,000 to $50,000 off your assessed value before the rate applies. Some states also cap how much taxable value can climb year over year, regardless of assessed value. Your tax bill is calculated on taxable value, not assessed value, so both numbers matter.

Can I appeal my property taxes without hiring a lawyer or a contingency firm?

Yes, and many homeowners do it and win. Informal reviews and equalization board hearings are built for property owners to represent themselves. You gather comparable sales, document any property record errors, and file before the deadline. Contingency firms usually take 25 to 40% of any refund or savings. Doing it yourself means you keep all of it. The process is procedural, not legal, in most jurisdictions.

Does getting a home improvement permit affect my assessed value?

Often yes. Pulling a permit for an addition, finished basement, or ADU signals to the assessor that you've added taxable value. The assessor may inspect after the permit closes and update your assessment. Cosmetic work like new paint or appliances generally doesn't trigger reassessment. The exact impact depends on your state's rules, but a significant structural addition almost always raises assessed value.

If I successfully appeal and reduce my assessed value, does it stay low permanently?

Not necessarily. A successful appeal lowers your assessed value for the current tax year and often carries into the next few. But assessors still reassess on their normal cycle, and if the market has risen, your value will likely climb again at the next reassessment. You may need to appeal again in future years if the new number lands above market value.

Sources

1. Alabama Department of Revenue, Property Tax Division: Alabama residential property is assessed at 10% of market value
2. International Association of Assessing Officers (IAAO), Standard on Ratio Studies: IAAO standards call for a median assessment-to-sale ratio of 90-110% and a coefficient of dispersion of 15% or less for residential property
3. University of Chicago Harris School of Public Policy, "The Regressivity of Property Taxation in American Cities" (2020): Assessment regressivity found in nearly every major county studied; lower-value homes assessed at higher ratios than high-value homes; private appraisal cost range cited
4. California State Board of Equalization, Proposition 13 Overview and Proposition 8 Information: Proposition 13 caps annual assessment increases at 2%; Proposition 8 allows temporary reduction when market value falls below assessed value
5. Texas Comptroller of Public Accounts, Property Tax Code Reference: Texas assesses at 100% of market value; protest deadline is May 15 or 30 days after the notice, whichever is later
6. New York State Department of Taxation and Finance, Understanding Property Tax: New York City uses 6% assessment ratio for Class 1 residential; assessment rules vary by county; typical appeal filing is in spring
7. Illinois Department of Revenue, Property Tax Assessment and Appeals: Cook County residential assessed at 10% of market value; other Illinois counties at 33.33%; boards of review typically meet in fall; appeal deadline typically 30 days from publication
8. Maryland Department of Assessments and Taxation: Maryland assesses at 100% of market value, phased in over three years; homestead properties capped at 10% annual increase
9. Florida Department of Revenue, Property Tax Overview: Florida assesses at 100% of market value; Save Our Homes limits increases to 3% or CPI, whichever is less; appeal deadline is 25 days from notice mailing
10. Appraisal Foundation, Uniform Standards of Professional Appraisal Practice (USPAP): USPAP defines market value as 'the most probable price a property should bring in a competitive and open market under all conditions requisite to a fair sale'
11. Lincoln Institute of Land Policy, Significant Features of the Property Tax: Lincoln Institute maintains a public database of assessment ratios and property tax rates across all 50 states
12. California State Board of Equalization, Assessment Appeals Guide: California appeal deadline is September 15 in most counties, or 60 days from the notice date, whichever is later