Appraisal vs. assessment: what the difference means for your appeal

Last updated 2026-07-11

What is the difference between an appraisal and an assessment?

An appraisal is one appraiser's opinion of what your specific house is worth. An assessment is the government's official value for taxing it. Those two numbers come from different people, different methods, and often different years. Knowing which one you're fighting is the whole ballgame.

The terms get swapped constantly at kitchen tables and in local Facebook groups. In a tax appeal they are not the same.

An appraisal is a professional opinion of market value produced by a licensed or certified real estate appraiser. It follows standardized methodology, usually the Uniform Standards of Professional Appraisal Practice (USPAP), and it results in a written report you can hand to a review board. ^[1]

An assessment is the value your county or municipality assigns your property for tax purposes. Most jurisdictions produce it through mass-appraisal: computer models that value hundreds of thousands of parcels at once using recent sales data, building permit records, neighborhood codes, and statistical adjustments. The International Association of Assessing Officers (IAAO) defines mass appraisal as "the process of valuing a universe of properties as of a given date using standard methods, employing common data, and allowing for statistical testing." ^[2]

The number on your tax notice is the assessment. It may or may not track the market value a licensed appraiser would reach for your specific property. That gap is what you exploit in an appeal.

One more wrinkle. Most states do not assess at 100% of market value. They apply an assessment ratio, sometimes called an "equalization rate" or "level of assessment." New York lets assessing units set their own ratios, some as low as 1% in certain municipalities. ^[3] California's Proposition 13 freezes assessed values at the 1975-76 base year value and caps annual increases at 2% until the property changes hands, which means assessed value can sit far below market. ^[4] Check your state's ratio before you decide your assessment is inflated.

Why does this distinction matter when you file an appeal?

You are not arguing that an appraiser made a mistake. You are arguing that the assessor's number is wrong for your property. The assessor built that number with a model. That's who you're up against, and the difference changes your whole strategy.

At a board of review you make one of three cases: the mass-appraisal model overvalued your specific property, a legitimate exemption never got applied, or comparable homes in your neighborhood carry lower assessments than yours (the equity argument).

Say you hire a private appraiser and the report comes back at $320,000 against an assessed value of $400,000. That appraisal is evidence. It is not automatically decisive. Many boards will ask whether the appraisal reflects value as of the assessment date (the "valuation date" or "lien date"), not the date you ordered it. An appraisal done six months after the tax year's valuation date can be challenged on relevance. ^[5]

The assessment, meanwhile, is presumed correct in most jurisdictions. The burden of proof sits with you. You can rebut that presumption with a credible appraisal, a strong set of comparable sales, or proof of factual errors in the assessor's property record card. ^[6]

So here's the practical version. You fight the assessment. You use an appraisal to fight it. You make the appraisal dates match the rules.

How does the assessor actually calculate your assessed value?

The assessor runs your house through a statistical model, not a walkthrough. Nobody visits. A computer estimates your value from data on file, then multiplies by the assessment ratio. Errors are common because the data is often stale or wrong.

Here is the basic process. The assessor's office collects recent arm's-length sales in your area and assigns your parcel to a "neighborhood code" or "stratum." A regression model estimates what your property would sell for based on square footage, lot size, age, condition, bedroom count, and similar traits. That becomes the assessor's market value estimate. The jurisdiction then multiplies by the assessment ratio to get the assessed value on your bill.

Trouble starts when the property record card has errors (wrong square footage is the classic), when your neighborhood code lumps dissimilar homes together, or when recent sales skew toward distressed or renovated properties that don't reflect typical condition.

The IAAO ratio study standards call for a median assessment-to-sale ratio between 90% and 110% of market value, and a coefficient of dispersion (a measure of uniformity) no higher than 15% for residential property. ^[2] Plenty of jurisdictions miss those marks. If your county's public ratio study shows a median ratio of 105%, your assessment may be systemically high before you even look at your individual parcel.

Your county assessor's website often publishes these ratio studies. Download one before you file anything.

What does a licensed appraiser do differently than the assessor?

A licensed appraiser shows up in person. The assessor's model does not. That single fact is why an appraisal can beat a mass-appraisal value: it captures the condition of your actual house on the actual day.

The appraiser photographs the property, measures it, notes condition problems the record card missed, and picks three to six genuinely comparable recent sales, then adjusts each one by hand for size, location, condition, and amenities. The result is a single-property opinion of value, as of a specific date, signed under penalty of professional license.

That inspection matters. A failing roof, foundation movement, or an HVAC unit original to 1987 all become condition adjustments in a competent report. Mass-appraisal models almost never catch them.

A full USPAP-compliant appraisal report (Form 1004 for single-family homes) runs roughly $350 to $650 in most markets, though price varies with property complexity and region. ^[7] A "desk review" or retrospective appraisal done from records without a site visit costs less and carries less weight with some boards.

Not every appeal needs a full appraisal. If the record card has factual errors, or your own comps show the assessment is clearly off, you can win without spending $500. But when the gap between assessed value and your evidence runs past 10 to 15%, and the dollars matter, a licensed appraisal usually pays for itself.

What is an assessment ratio and how does it affect what you owe?

The assessment ratio is the percentage of market value your property is supposed to be assessed at. Sometimes it's called the equalization ratio or fractional assessment rate. It swings hard from state to state, and sometimes by property class within one state.

Here is a simplified comparison across several common states:

State	Residential Assessment Ratio	Notes
California	~1% of 1975-76 base value, +2%/yr max (Prop 13)	Resets to market on sale [4]
Illinois (Cook County)	10% of market value (residential)	Other classes differ [8]
New York	Varies by municipality, set locally	Some towns assess at 100% [3]
Texas	100% of market value	Property tax funds schools; no state income tax [9]
Florida	100% of just value	SOH cap limits annual increase to 3% or CPI [10]
Georgia	40% of fair market value	Statewide statutory rate [11]

The ratio matters for two reasons. First, you have to compare the right numbers. If Georgia assesses at 40%, a $200,000 home should carry an $80,000 assessed value. A $100,000 assessed value on that home implies a $250,000 market value estimate, which may be wrong. Second, when you gather comps, you work backward from market value through the ratio to the expected assessed value.

For counties with tangled local rules, like Cook County or Los Angeles County, pin down the ratio structure before you file. It saves a lot of confusion later.

Can you use a private appraisal as evidence in a property tax appeal?

Yes, in most jurisdictions, and it's often the strongest evidence you can bring. But it has to meet a few requirements or a board will discount it.

First, the appraisal must be retrospective. It has to opine on value as of the tax year's valuation date, not the date the appraiser walked through. Most states set that date somewhere between January 1 and April 1 of the tax year. ^[5] If you order an appraisal in September for a January 1 valuation date, a good appraiser uses sales that closed on or before January 1 and writes the report as a retrospective opinion.

Second, some boards require the appraiser to be licensed in the state where the property sits. Almost always true, but confirm it in your local rules.

Third, the appraiser's comps and any comps you gathered yourself should tell the same story. If your private appraisal pulls sales from a different neighborhood or a different time window than your own comps, the board may pick at the methodology.

Here's the money part. Some contingency-fee tax appeal firms hire appraisers as part of their service, then take 25 to 40% of your first-year savings. If you do this yourself, you keep the whole reduction. Tools like the TaxFightBack appeal kit walk you through building the evidence package on your own.

What is the difference between market value and assessed value on your tax bill?

Market value is what your home would sell for. Assessed value is that number multiplied by the assessment ratio, and it's the figure your tax rate actually hits. One is the sale price; the other is the taxable base.

Market value, precisely, is what a willing buyer would pay a willing seller in an arm's-length deal, neither side under pressure, both reasonably informed. Most state statutes require assessors to approximate it. ^[6]

Your bill works like this: Assessed Value x Mill Rate = Tax Before Exemptions.

If your assessed value is $300,000 and your mill rate is 20 mills (2%), your gross tax is $6,000. Knock the assessed value down to $250,000 and you save $1,000 a year, every year, until the next reassessment.

Some states print both numbers on the notice (California shows assessed value and the "base year value"). Others show only the assessed value and expect you to know the ratio. Georgia, at 40% of fair market value, shows a $120,000 assessed value on a home the assessor pegs at $300,000. If you think it's worth $250,000, your target assessed value is $100,000.

Texas has no ratio. Assessed value is supposed to equal market value, so any gap you demonstrate is a direct dollar-for-dollar argument. The Bexar County Tax Assessor page shows how the Bexar Appraisal District notice breaks out market value and taxable value separately.

What are the grounds for appealing an assessment, and which ones actually work?

There are four grounds for appeal, and they are not equally good. Factual errors and overvaluation win the most money. Equity arguments work in the right places. Exemption fixes are the fastest. Here's how each one plays out.

1. Factual error. The record card says 2,400 square feet; you have 1,900. Or it lists a finished basement you don't have. These are the easiest wins because the assessor's own data is wrong. Pull your record card from the assessor's website and check every field.

2. Overvaluation. The assessor's market value estimate is higher than what your home would actually sell for, based on recent comparable sales. This is the most common ground and the one that takes the most evidence.

3. Inequity. Even if your assessment matches market value, nearby similar homes are assessed at a lower percentage of their actual value. This is a uniformity or equity argument. It's valid in most states, harder to document, and sometimes heard by a different board than value appeals.

4. Denial of exemption. Your homestead, senior, or veteran exemption never got applied or got applied wrong. This is more administrative than a value fight, and it's usually the quickest to fix.

The biggest dollar reductions come from factual error (one corrected data point can cut assessed value 20 to 30%) and overvaluation backed by a licensed appraisal. Equity arguments land regularly where assessment uniformity is poor, like some Illinois townships. The Gwinnett County Tax Assessor site in Georgia even offers an online equity search tool in its public data.

For commercial or larger residential properties in places like Montgomery County or Hennepin County, overvaluation cases often need an income-approach appraisal on top of the sales-comparison approach.

How do deadlines for property tax appeals work, and what happens if you miss them?

Miss the deadline and you're done for the year. No do-overs in most states. The window is set by statute, not assessor policy, and it's almost always short. File early.

Typical windows run 30 to 90 days from the date your assessment notice is mailed. A few examples:

• Texas: Protest deadline is May 15 or 30 days after the appraisal notice is mailed, whichever is later. ^[9]
• Illinois (Cook County): Depends on your township's open filing window, published annually by the Assessor. Residential windows are typically 30 days. ^[8]
• California: The Assessment Appeal application is filed between July 2 and November 30 for the regular roll in most counties. ^[4]
• Florida: The petition to the Value Adjustment Board is due within 25 days of the TRIM notice mailing. ^[10]
• New York: Grievance Day is typically the fourth Tuesday in May; some localities differ. ^[3]
• Georgia: The appeal must be filed within 45 days of the assessment notice date. ^[11]

Miss the window and your only remaining option in most states is to wait for the next assessment cycle, or file a complaint about procedural error, which is a much harder lift.

Boards don't grant extensions for "I didn't know." The notice states the deadline on its face. Read it the day it lands.

Do you need a licensed appraiser to win a property tax appeal, or can you use your own comps?

No, you don't always need an appraiser. Plenty of homeowners win informal hearings with a printed spreadsheet of five or six recent sales pulled from Zillow, Realtor.com, or the county recorder, plus photos of condition problems the assessor missed.

The informal hearing (sometimes an "informal conference" or "assessor review") is the first step in most appeal processes. Here the assessor's staff can settle. A clean set of comps showing your home is worth 10% less than assessed is often enough. If the informal round fails, you move to the formal board of review or equalization board, where the evidence bar rises.

Formal boards vary. Some accept homeowner comps on a simple grid. Others expect a formal appraisal or an appraiser to testify. Check your jurisdiction's rules before you spend money on a full appraisal.

Nobody has clean national data comparing win rates for self-represented versus appraiser-represented appellants at formal boards. The closest evidence comes from Lincoln Institute of Land Policy research showing the appeal process produces meaningful reductions across jurisdictions, but representation type isn't tracked systematically in public data. ^[12] Anecdotally, a credible private appraisal makes a board far more willing to reduce, especially when the reduction sought is large.

For NYC property tax appeals, the Tax Commission accepts income-approach evidence for co-ops and condos, which usually needs professional preparation.

What should you actually do first when you get your assessment notice?

Open it the day it arrives. The deadline clock starts on the mailing date, and most people let the envelope sit until it's too late.

Step one: find the valuation date and the appeal deadline. Both should be on the notice or the instructions. If not, look them up on the assessor's website or call the office.

Step two: pull your property record card. Every county assessor should have this online now. Check every field: square footage, bedroom count, bath count, basement finish status, garage type, year built, condition rating. Errors here are common and easy to fix.

Step three: gather comparable sales. Use your county's public sales data (often on the assessor or recorder site), Zillow, or Redfin. Look for homes that sold within 6 to 12 months of your valuation date, within half a mile if you can, similar in size and age. Adjust mentally for differences: if a comp has a remodeled kitchen and yours doesn't, drop the comp's sale price before comparing.

Step four: estimate what a licensed appraiser would conclude. If your comps cluster around a value 10% or more below your assessed value (after accounting for the ratio), you have a viable appeal.

Step five: file. Even with incomplete evidence, file to preserve your right. You can strengthen the record before the hearing date. Missing the deadline ends the whole conversation.

For complex ownership structures or commercial uses, sites like Santa Clara property tax and LA County property tax publish appeal instructions built for their local rules.

How often do property tax appeals succeed, and how much can you save?

More often than most people expect. Success rates run wide by jurisdiction and hinge on how well you prepare, but the odds are good enough that filing is worth it in most cases.

The Lincoln Institute of Land Policy has documented that a large share of residential appellants who file achieve some reduction. ^[12] Cook County, Illinois has reported that in recent years roughly 60 to 70% of residential appeals that ran through the process got some reduction, though the average cut is modest for small single-family homes.

Texas data is more granular. The Texas Comptroller's property value study shows that Appraisal Review Board protests produce reductions for roughly 55 to 60% of residential protesters statewide in recent years, with average savings running from the hundreds into the low thousands per successful case depending on property value. ^[9]

The upside repeats. A $3,000 annual reduction compounds across a reassessment cycle. If your county reassesses every three years, one win is worth $9,000, and a lower assessed value also becomes the starting point for the next cycle.

A self-filed appeal usually costs nothing in filing fees (most residential appeals are free), plus whatever you spend on an appraisal if you go that way. Contingency firms take 25 to 40% of first-year savings. Do it yourself and you keep all of it.

Frequently asked questions

Is the assessed value the same as the market value of my home?

No. Assessed value comes from market value multiplied by your jurisdiction's assessment ratio, which ranges from about 10% (Cook County, Illinois residential) to 100% (Texas). Even states that nominally assess at 100% often produce assessed values that diverge from true market value, because mass-appraisal models rely on historical sales data and can't fully capture the condition of an individual property.

Can I appeal my property tax assessment without hiring anyone?

Yes. Nearly all informal hearings and many formal board hearings allow self-representation. You need a copy of your property record card, a spreadsheet of recent comparable sales, and photos if condition is an issue. Formal boards in some jurisdictions expect more structured evidence, but homeowners win routinely without attorneys or appraisers, especially at the informal stage.

What is a retrospective appraisal and do I need one for my appeal?

A retrospective appraisal values your property as of a past date, usually the tax year's valuation date (often January 1). Most states require appeal evidence to reflect value as of that date, not the current date. If you hire an appraiser mid-year, ask for a retrospective opinion. Without it, the board may discount the appraisal for using the wrong time period.

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

The assessment ratio is the fraction of market value your property is supposed to be assessed at. Your state's department of revenue or taxation publishes it, often in an annual equalization report or ratio study. Your county assessor's website may list it too. Georgia's is 40% by statute, California's is effectively very low for long-held homes under Proposition 13, and Texas is 100%.

How long does a property tax appeal typically take?

Informal hearings usually get scheduled within 30 to 60 days of filing and resolve fast, sometimes the same day. Formal board hearings can take 3 to 9 months depending on backlog. Large urban jurisdictions in Illinois and New York can stretch to a full year. You generally keep paying your current bill while the appeal is pending, then get a refund or credit if you win.

What happens if my property tax appeal is denied?

You can usually appeal to a higher tribunal: a state Board of Equalization, Tax Court, or Circuit Court depending on the state. Each level has its own filing deadline, often 30 to 90 days from the lower decision. State Tax Courts typically allow more formal discovery and full appraisal evidence. Beyond that, options include state appellate courts, where professional legal representation is generally necessary.

Does getting a home appraisal affect my property taxes?

A private appraisal you order for yourself does not automatically change your assessment. The assessor never sees it unless you submit it as evidence in an appeal. If you submit it and win, the lower assessed value typically carries forward until the next reassessment. A purchase appraisal sent to a lender is also not shared with the assessor, though a recorded sale price becomes public data that can influence future assessments.

What is the difference between an equalization rate and an assessment ratio?

They measure the same thing from different angles. The assessment ratio is the target percentage of market value the assessor aims to assess at. The equalization rate (used heavily in New York) is the actual measured ratio of assessed value to market value across a municipality, calculated by the state after comparing assessments to recent sales. If the equalization rate sits below the target, some properties may be over-assessed relative to others.

Can I use Zillow's estimate as evidence in my property tax appeal?

You can submit it, but boards give it little weight. Zillow's Zestimate is an automated value estimate with a published median error rate of roughly 2 to 3% for on-market homes and higher for off-market ones. Boards prefer actual closed sales with specific addresses, dates, and prices. Use Zillow to spot candidate comparable sales, then verify each one through your county recorder's public records.

What is a property record card and why does it matter for my appeal?

The property record card is the assessor's internal data file for your parcel. It lists every characteristic the mass-appraisal model uses: square footage, lot size, construction quality grade, condition rating, bathroom count, garage type, and any improvements. Errors on this card directly inflate your assessed value. Reviewing it is the first thing every homeowner should do before deciding whether to appeal.

How do I find comparable sales to support my property tax appeal?

Start with your county assessor or recorder's public sales database, which is free and shows recorded deed prices. Filter for residential sales within 6 to 12 months of your valuation date, within half a mile, similar in size (plus or minus 20%) and age. Aim for at least five comps. Note differences in condition, lot size, or features, and be ready to explain why those differences support a lower value for your property.

Do property tax appeal deadlines differ from appraisal notice dates?

Yes, and the gap can be short. The appraisal (assessment) notice arrives first. Your appeal deadline is typically 30 to 90 days after that mailing date, set by state statute, not by when you open the envelope. Texas gives 30 days from notice or until May 15. Florida gives 25 days. New York uses a fixed Grievance Day. Missing this window almost always means waiting a full year for the next cycle.

Can commercial property owners use the same appeal process as homeowners?

The same boards hear both, but commercial appeals need more sophisticated evidence. Income-producing properties should be supported by an income-approach appraisal using actual rent rolls, vacancy rates, and capitalization rates rather than sales comps alone. Many jurisdictions apply different assessment ratios to commercial property. Cook County, for example, assesses commercial property at 25% of market value versus 10% for residential.

What is the difference between an informal hearing and a formal appeal board hearing?

An informal hearing is a meeting with assessor's staff where both sides discuss value without formal rules of evidence. Many reductions happen here. A formal board hearing is a quasi-judicial proceeding where you present evidence, sometimes under oath, and the board issues a written decision. Evidence standards are higher at the formal level, and an appraisal carries much more weight there than a printout of Zillow listings.

Sources

1. Appraisal Foundation, USPAP (Uniform Standards of Professional Appraisal Practice): USPAP sets the standards for professional appraisal practice in the United States, governing licensed appraisers' methodology and report content
2. International Association of Assessing Officers (IAAO), Standard on Ratio Studies: IAAO defines mass appraisal as 'the process of valuing a universe of properties as of a given date using standard methods, employing common data, and allowing for statistical testing,' and sets residential COD standards at 15% or below
3. New York State Department of Taxation and Finance, Property Tax and Assessment: New York allows assessing units to set their own assessment ratios, and Grievance Day is typically the fourth Tuesday in May
4. California State Board of Equalization, Proposition 13 Overview: Proposition 13 limits assessed value increases to 2% per year and resets to market value on sale; assessment appeal window runs July 2 to November 30 for the regular roll
5. Appraisal Institute, Guide Note 10: Reviewing Appraisals: Appeal evidence appraisals should reflect value as of the jurisdiction's valuation date (the lien date or assessment date), not the date of the inspection
6. International Association of Assessing Officers (IAAO), Property Assessment Administration: In most jurisdictions the assessment is presumed correct and the burden of proof rests with the appellant to rebut that presumption with credible evidence
7. HomeAdvisor / Angi, Cost to Get a Home Appraisal: Full residential appraisal costs typically range from $350 to $650 for standard single-family homes depending on market and property complexity
8. Cook County Assessor's Office, Appeals: Cook County residential properties are assessed at 10% of market value; residential appeal windows are approximately 30 days per township, published annually
9. Texas Comptroller of Public Accounts, Property Tax: Texas assesses at 100% of market value; protest deadline is May 15 or 30 days from notice; roughly 55-60% of residential protesters achieve reductions annually
10. Florida Department of Revenue, Property Tax Oversight: Florida assesses at 100% of just value; TRIM notice petition deadline is 25 days from notice mailing; Save Our Homes cap limits annual increases to 3% or CPI whichever is lower
11. Georgia Department of Revenue, Property Tax: Georgia assesses residential property at 40% of fair market value by statute; appeals must be filed within 45 days of the assessment notice date
12. Lincoln Institute of Land Policy, Property Tax Assessment Appeals: Lincoln Institute research documents that a significant share of residential appellants who file achieve reductions, though win rates vary substantially by jurisdiction