What is a property tax assessment?
A property tax assessment is your county government's official estimate of your home's market value. That number is used as the base for calculating how much you owe in property taxes each year. The formula looks like this:
The assessment ratio varies by state (some assess at 100% of market value; others at 40% or 70%). The millage rate is set by your local taxing authorities — city, county, school district — and changes annually based on budget needs.
The assessor's job is to estimate market value at scale. In a county with 500,000 parcels, no one is walking through your home. Assessors use mass appraisal models — automated formulas applied to broad data like square footage, year built, and recent sales in your zip code. These models are fast and cheap. They are also wrong for a staggering number of properties.
A 2020 University of Chicago study found that property tax systems are regressive — lower-value homes are systematically overassessed relative to higher-value homes in the same county. This isn't an accident. It's the predictable output of algorithms applied to a market where data quality degrades at the lower end. The county collects more from the people least able to fight back.
Every year you pay taxes based on an overassessed value, that money is gone. Counties do not proactively correct their own errors. You have to find the mistake and force the correction yourself. That process is called an appeal — and it's designed to seem harder than it is.
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How to know if you're overassessed
The single most reliable indicator of overassessment is a gap between your assessed value and what comparable homes in your area actually sold for. But there are several other signals worth checking before you dig into comparables.
Your assessed value exceeds recent market sales
Pull 3–5 recent sales of similar homes (same neighborhood, similar size and age). If they sold for less than your current assessed value, that gap is your case. County assessors use this same data — if they missed it, you can correct them.
Your neighbor's similar home is assessed lower
Property assessment data is public record. Your county posts every parcel's assessed value online. If the house next door is 200 sq ft larger and assessed $30,000 less than yours, that inconsistency alone is grounds for appeal under 'equalization' principles — you should be taxed uniformly relative to comparable properties.
Your assessment jumped far more than the market
If home values in your area rose 8% but your assessment went up 22%, that disproportion warrants investigation. Large reassessment years often contain errors because counties process thousands of updates simultaneously using outdated models.
Your property has significant damage or defects
Foundation issues, roof damage, outdated systems, flood zone restrictions, easements — physical or legal conditions that reduce market value are often invisible to mass appraisal models. If your home couldn't sell for its assessed value, that's a factual argument.
You bought your home below its assessed value
A recent arm's-length purchase price is among the strongest evidence you can present. If you paid $310,000 for a home assessed at $380,000, your own transaction establishes market value. The burden of proof flips: the county must explain why they think it's worth more than what a willing buyer actually paid.
The national overassessment rate is 40.5% — not a rounding error.
Lincoln Institute of Land Policy analysis of 39 million parcels found that the median effective tax rate on overassessed homes is more than twice the rate paid by similarly-valued underassessed homes in the same county. This is systematic, not occasional. If you haven't checked, the odds are meaningful that you're on the wrong side of it.
Step-by-step: the property tax appeal process
The appeal process has five stages, and every state follows a version of this same structure. The details — deadlines, filing fees, which board hears the case — vary by jurisdiction, but the logic is identical everywhere.
Get your current assessment and deadline
Your county mails a Notice of Assessment (or Notice of Value) once per year, typically in spring. This document states your assessed value and your deadline to appeal — which is almost always printed on the notice itself. Do not set it aside. Most counties give you 30–90 days from this mailing date. Missing the deadline means waiting an entire year. Go to your county assessor's website and pull your full property record: square footage, year built, bedroom/bath count, and any features that affect value. Errors in these records — an extra bathroom listed that doesn't exist, or 200 phantom square feet — are free points in your favor.
Research comparable sales
Comparable sales — 'comps' — are the backbone of every successful appeal. You need recent (within the last 6–12 months) sales of similar homes: same neighborhood, similar square footage (within 15–20%), similar age, similar condition. Pull these from Zillow, Redfin, Realtor.com, or your county's own property sales database (which is public record in every state). Look for 3–5 sales where the sold price was lower than your assessed value. Calculate: if your home is assessed at $400,000 and three similar homes sold for $330,000–$355,000, you have a clear argument. Document the addresses, sale dates, sale prices, and how they compare to your property.
File the appeal
Most counties allow you to file online now. Search '[your county] property tax appeal' or '[your county] board of equalization.' The initial filing is typically a one-page form asking for your parcel number, your estimated fair market value, and a brief reason for the appeal. You do not submit all your evidence at this stage — you're simply opening the case. Some counties charge a filing fee ($25–$75). Some require no fee for owner-occupied residential properties. Pay it if required. The cost is trivial relative to what you stand to recover.
Informal review (most counties)
Before a formal hearing, most counties offer an informal review with an assessor's staff member. This is your best opportunity to resolve the appeal quickly. Bring your comps, your property record printout, and any photos of issues. Present the case clearly: 'My home is assessed at $X. Here are three sales of comparable properties that closed within the last year at $Y–$Z. I'm requesting the assessment be reduced to [your estimate of fair value].' Many overassessments are corrected at this stage without going further. If the informal review doesn't produce a satisfactory result, you escalate to the formal hearing.
Formal hearing (if needed)
The formal hearing is held before a Board of Equalization, Board of Assessment Review, or similarly named panel — depending on your state. You present your evidence, the county presents theirs (usually the assessor's model output), and the board makes a binding decision. You don't need a lawyer. You do need to be organized: numbered exhibits, a clear narrative, and a specific number you're requesting. The board is not hostile — they're looking for evidence that the assessment is inconsistent with market value. If you have it, they will generally act on it. If the formal hearing doesn't go your way, you have the right to escalate to your state's tax court, though that level of escalation rarely makes sense for residential properties under $1M.
Before you start: see if your assessment is actually off.
We pull your county's assessment record and compare it against recent comps automatically. If there's a gap, we show you the number — and exactly how big it is.
Evidence that wins property tax appeals
Assessment boards are not impressed by frustration. They are moved by data. The strength of your case is almost entirely determined by how clearly your evidence shows the assessed value is inconsistent with market value. Here's what actually works — ranked by persuasive weight.
Comparable sales
Very High3–5 recent closed sales (within 6–12 months) of similar homes in your neighborhood or zip code, all with sale prices below your assessed value. This is the same methodology assessors are supposed to use — when you show better data, it's hard for them to argue with their own standard.
Pro tip
Use the county's own sales database if available. Public records sources carry more weight than Zillow alone. Organize comps in a table with address, sale date, sale price, sq footage, and price per sq foot.
Independent appraisal
Very HighA licensed appraiser's report setting your home's market value below the assessed value. This is the gold standard — a professional opinion that uses the same legal framework assessors use. It's also the most expensive option ($300–$600). Only worth it when the potential savings are large enough to justify the cost.
Pro tip
Tell the appraiser you need the report for a tax appeal, not a refinance or sale. This changes the effective date and scope of the analysis.
Your purchase price (if recent)
HighIf you bought the home within the last 1–2 years at arm's length, your purchase price establishes market value better than any model. Courts consistently hold that a recent sale price is the best evidence of market value because it reflects what an informed buyer actually paid.
Pro tip
Bring your HUD-1 settlement statement or closing disclosure. Make sure the sale was arm's-length (not a foreclosure, family transfer, or estate sale).
Property condition documentation
ModeratePhotographs, contractor estimates, and inspection reports documenting structural issues, deferred maintenance, or functional obsolescence that reduce market value. A flooded basement, aging HVAC, failing foundation, or fire damage that the assessment model doesn't know about.
Pro tip
Before your hearing, document everything with timestamped photos. Get written estimates from licensed contractors. Don't just describe problems — price them.
Assessment record errors
ModerateYour county's own records may list wrong square footage, extra bathrooms that don't exist, a garage that was demolished, or a pool that was filled in. These are pure fact errors — no market analysis required. When the county's model says your house is 2,400 sq ft and it's actually 1,850 sq ft, that discrepancy alone justifies a significant reduction.
Pro tip
Pull your county's full property record card before your hearing. Measure your home if needed. Errors in assessed square footage are more common than most homeowners realize.
Assessment inequity
ModerateIf comparable properties in your neighborhood are assessed significantly lower on a per-square-foot basis, that inconsistency violates the equity principle of assessment law — properties should be taxed uniformly. This argument supplements comparables but rarely stands alone.
Pro tip
Pull assessed values for 5–10 nearby similar properties from the county's public records. Create a per-sq-ft analysis showing you're assessed above the neighborhood median.
State-by-state appeal deadlines
Missing the deadline means waiting a full year to appeal. The window is short — typically 30–90 days from your notice of assessment. Check your county specifically; deadlines vary within states, especially in large states like New York, California, and Illinois.
File with county Board of Equalization
Appraisal Review Board hearing
Assessment Appeals Board
Value Adjustment Board
Assessment Review Commission
Board of Review; Cook County is separate
County Tax Board
Board of Assessment Appeals
County Board of Revision
March Board of Review for informal
County Board of Equalization
County Assessor; escalate to Board of Equalization
County Assessor or State Board of Equalization
Assessor's office first; then Appellate Tax Board
Board of Equalization
Deadlines change. Always verify with your specific county assessor's office or website. This table reflects general state patterns as of 2026.
Don't let the deadline catch you off guard.
We check your assessment the moment you enter your address — so you know immediately whether you have a case worth pursuing before the window closes.
Success rates and what to expect
The property tax appeal system is designed to discourage participation. The forms are confusing, the deadlines are short, the process is unfamiliar. The county counts on the vast majority of overassessed homeowners doing nothing. And for the most part, they're right — fewer than 5% of eligible homeowners file appeals in any given year.
For the 5% who do: the outcomes are good. Here's what the data shows.
When homeowners research and file their own appeal with decent comparable evidence, roughly half receive a reduction.
Professional services with access to MLS data and prior hearing experience consistently hit these rates on cases they accept.
ATTOM Data Solutions analysis of property tax appeals nationally. High-tax states (NJ, IL, NY) average 2–4x this figure.
The most important variable is not whether you hire help — it's whether you have evidence. An unrepresented homeowner with three solid comps beats a poorly prepared professional. Evidence is the product; representation is the delivery mechanism.
The risk of filing is nearly zero. In virtually all jurisdictions, filing an appeal cannot result in your taxes being raised. The board reviews whether the current assessment is accurate — they are not looking for reasons to increase it. The worst outcome is that the appeal is denied and your taxes stay the same. Most homeowners who don't appeal simply assume that's already the outcome. For 40% of them, they're wrong.
The savings compound. A $20,000 assessment reduction in a county with a 1.5% effective tax rate saves you $300 per year. Over 10 years — before the next major reassessment cycle — that's $3,000. In high-rate areas (New Jersey averages 2.2%, Illinois averages 2.1%), that same $20,000 reduction is worth over $4,000 over the same period.
The system is designed to overcharge you.
A 2021 ProPublica/Chicago Tribune investigation found that in Cook County alone, the assessment system produced "a wildly inaccurate, unfair picture of property values" that consistently burdened lower-value properties more than higher-value ones. The assessor's office argued the errors were random. The data showed they were systematic. Cook County is an extreme case — but the underlying dynamic (mass appraisal errors that disproportionately hit less expensive properties) exists in nearly every county in the country.
DIY vs. using a professional service
Property tax appeals are one of the few legal processes specifically designed for non-lawyers. The informal hearing is a 30-minute conversation. You don't need a law degree. You need organized evidence and a number you can defend. Whether to do it yourself or hire help comes down to a simple calculation.
Do it yourself
Cost: $0–$75 (filing fee only)Use a service
Cost: 25–40% of first-year savings (contingency)The contingency model: why it aligns incentives
Most professional tax appeal services work on contingency — you pay nothing unless they win, and then you pay a percentage (typically 25–40%) of your first-year savings. Year two onward, you keep everything. This model is important because it means the service only takes cases they believe they can win. If your evidence is weak, a good contingency firm won't take your case — which is itself a useful signal.
Be cautious of services that charge upfront fees regardless of outcome. The contingency model puts the service's incentive squarely on getting your assessment reduced, not just filing paperwork. Ask any service you consider: "What percentage of cases you accept result in a reduction?" A reputable service should answer above 80%.
The DIY guide: what you actually need
If you decide to handle it yourself, here is exactly what to bring to an informal hearing:
See your number first — then decide how to handle it.
We show you the full picture: your assessed value, what comparable homes sold for, and how much you're likely overpaying. Then you choose: DIY with our free guide, or let us handle it for you on contingency.
Frequently asked questions
Straight answers. No hedging.
How long does a property tax appeal take?
Most counties resolve appeals in 3 to 9 months. Some take longer — Cook County, Illinois averages 12–18 months. Georgia counties typically resolve in 3–6 months. Filing early in your county's window gives you the most time to gather evidence.
What are the chances of winning a property tax appeal?
Nationally, roughly 40–60% of appeals result in a reduction when filed by homeowners who do their own research. With professional representation and a data-backed case, success rates reach 80–90%. The key variable is whether you have solid comparable sales evidence — without it, counties have little reason to lower your assessment.
What evidence do I need to appeal my property taxes?
The strongest evidence is comparable sales — recent sales of similar homes in your area assessed or sold for less than your assessed value. You also need your county's assessment record for your property (free from the county assessor website), photos of any damage or disrepair, and, if available, a recent independent appraisal. Sales comps carry the most weight.
Can I appeal my property taxes if I just bought my home?
Yes — and buying at a price below the assessed value is actually strong evidence of overassessment. Your purchase price is an arm's-length transaction that establishes market value. If you paid $320,000 and your assessment is $375,000, that gap is your evidence.
What happens if I lose my property tax appeal?
Nothing happens. Your taxes stay the same as the current assessment. You are not penalized for filing, and in most counties your taxes cannot be increased because you appealed. The only cost is your time — or your representative's fee if you hired one.
Can the county raise my taxes if I appeal?
In a small number of states, a review board can theoretically raise your assessment during an appeal. However, this is rare and typically requires evidence that you are significantly underassessed. Most counties simply review whether your current assessment is accurate — they are not looking for reasons to charge you more.
What is the deadline to appeal my property taxes?
Deadlines vary by state and county, typically ranging from 30 to 90 days after your annual notice of assessment is mailed. The most common deadline windows are April through June. Missing the deadline by even one day means waiting a full year to appeal. Check your specific county assessor's website immediately after receiving your notice.
Do I need a lawyer or professional to appeal?
No — most informal hearings are designed for homeowners to represent themselves. You need organized evidence and a clear argument, not legal training. Professional services become valuable when the potential savings are large (several thousand dollars per year), the evidence is complex, or you simply don't have time to prepare the case yourself.
How do I find my property's assessed value?
Your county assessor publishes this on their website. Search '[your county] property assessor' or '[your county] property tax records.' You can also find it on your annual tax bill. The assessed value may be different from the appraised value or market value — make sure you are looking at the number used to calculate your tax.
How much can I save by appealing my property taxes?
The average successful appeal reduces the assessment by $15,000–$50,000, translating to $300–$1,500 per year in tax savings depending on your local millage rate. In high-tax areas like New Jersey, New York, and Illinois, savings from a successful appeal can exceed $3,000 per year. These reductions compound — you save that amount every year until your next reassessment.
Your county is counting on you not checking.
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