How to check comparable home sales for a property tax appeal

Last updated 2026-07-09

Why comparable sales are the backbone of any property tax appeal

Your property tax bill starts with an assessed value. That value is supposed to reflect what your home would sell for on the open market, usually as of a specific "lien date" or "valuation date" set by state law. If the assessor got that number wrong, comparable sales are how you prove it.

Comparables, or comps, are the same tool appraisers and assessors use when they set your value in the first place. Mass appraisal systems used by county assessors apply automated models to thousands of sales at once ^[1]. Those models can misclassify a home's size, miss a functional problem, or use sales that don't reflect your specific neighborhood. When that happens, comps from the real market tell the real story.

Appraisal review boards and hearing officers are not swayed by how unfair your tax bill feels. They respond to evidence. A set of three to five recent, nearby sales priced below your assessed value is the clearest, most portable form of evidence you can bring. It's the same standard used in formal appraisal under the Uniform Standards of Professional Appraisal Practice (USPAP), and most state appeal statutes explicitly allow sales evidence ^[2].

This is not complicated work. You do not need a licensed appraiser to gather comps for an informal appeal, though a certified appraisal is stronger for formal hearings. What you need is the right sources, the right selection criteria, and a simple adjustment grid.

What makes a comparable sale actually comparable?

Not every nearby sale qualifies. Assessors and review boards apply selection criteria, and you should too, or your comps will get dismissed.

The standard criteria:

Factor	Preferred range	Why it matters
Sale date	Within 12 months of valuation date	Markets shift; stale sales lose weight
Distance	Within 0.5 to 1 mile (urban); up to 3 miles (rural)	Neighborhood conditions drive value
Gross living area (GLA)	Within 15-20% of subject	Size is the single biggest value driver
Year built	Within 10-15 years	Age affects condition, systems, and style
Style	Same or similar (ranch to ranch, colonial to colonial)	Story count affects livability and cost per sq ft
Condition	Similar, or adjusted for	A renovated comp makes your dated home look undervalued
Lot size	Within 25-30% (suburban); case-by-case (rural)	Acreage adds value in some markets
Sale type	Arms-length transactions only	Foreclosure, estate, or related-party sales skew data

Arms-length means a willing buyer and willing seller with no pressure or relationship. Most Multiple Listing Service (MLS) sales qualify. A bank foreclosure, a family transfer, or a sale marked "as-is" under duress usually does not ^[3].

Condition is the factor that trips up most DIY filers. If your three comps all have renovated kitchens and yours does not, you need to either note that your home's value should be lower for that reason, or find comps that actually match your condition. An honest comp set will include a note on any differences you cannot eliminate by selection alone.

Where to find comparable home sales in your area

You have more free sources than you probably realize.

Your county assessor's website. This is the first stop. Most county assessors publish a searchable database of sales. Search by subdivision, zip code, or map polygon. Filter to the past 12-24 months. Some counties (Cook County in Illinois, Los Angeles County in California, Maricopa County in Arizona) have detailed online portals that show sale price, sale date, and property characteristics side by side ^[4]. If you're appealing in one of those larger metro areas, see our guides on Los Angeles county property tax and Maricopa property tax for county-specific search instructions.

Zillow's sold listings. Go to Zillow, type your address, and click "Recently Sold" on the map. Filter by home type, beds, baths, and square footage. Zillow pulls data from MLS feeds and county records. The sale price and date shown are real, though the "Zestimate" is irrelevant for your purposes, so ignore it entirely.

Realtor.com and Redfin. Both show sold listings with photos, which matters. Photos let you assess condition without driving to every address. Redfin in particular shows price per square foot on its map view, which makes it fast to spot whether your neighborhood's going rate is above or below your assessed value.

Federal Housing Finance Agency (FHFA) House Price Index. The FHFA publishes a free public tool at fhfa.gov that shows price change trends by metro area and ZIP code going back to 1991 ^[5]. This is useful context, not a comp source, but it helps you argue that prices in your market fell or stagnated after the assessor's valuation date.

Your state's public records portal. Many states (Florida, Texas, Wisconsin, for example) require deed recording with sale price, and those records are public. Florida's county property appraiser sites are especially detailed. Texas counties like Bexar publish deed transfer prices and assessment records together, which you can cross-reference at the Bexar County tax assessor portal.

Neighborhood sales data from a local agent. You don't have to hire a buyer's agent to ask for a comp pull. Many agents will run a quick CMA (Comparative Market Analysis) as a courtesy, especially if you mention you're appealing a tax assessment. The CMA printout makes good exhibit material, though you should verify the underlying sales independently.

Nobody has a single perfect free database that covers every county. The closest to universal coverage is your county assessor's site, which is why it's always the first source.

How many comps do you need, and how recent is recent enough?

Three comps is the practical minimum for an informal appeal. Five to six is stronger. Beyond eight, you're adding noise more than weight, unless you're building a statistical argument with a larger dataset.

Recency rules vary by state. Most assessors use a valuation date (sometimes called the "assessment date" or "lien date") that is anywhere from six months to 18 months before you receive your notice. The key is matching your comps to that date, not to today.

Here's why that matters: if your valuation date is January 1, 2024, and the market ran up 8% between January 2024 and the day you file your appeal in May 2025, the assessor will argue your current-day comps don't reflect the market as of the valuation date. Stick to sales that bracket the valuation date, ideally three to six months before and three to six months after. If the market was falling, sales after the valuation date actually help your case.

A few states allow a longer lookback. In California, Proposition 13 limits annual increases to 2% except after a change in ownership or new construction, so comps are sometimes used to argue a base year value was set too high ^[6]. In Illinois, the assessment cycle runs three years in Cook County, and you may be appealing a value set on sales from a prior triennial ^[4]. Know your state's specific valuation date before you pull comps.

If you genuinely cannot find three arms-length comps within 12 months, expand the radius before you expand the time window. A sale two miles away from six months ago beats a sale one mile away from 30 months ago.

How do you adjust comparable sales for differences from your home?

Raw comp prices are a starting point, not a final answer. Every meaningful difference between a comp and your subject property requires an adjustment. This is where most DIY filers either skip the work and lose credibility, or overcomplicate it and confuse the board.

The goal is simple: what would each comp have sold for if it were identical to your home? You adjust upward if the comp is inferior to your home (it sold for less because it has something your home lacks), and you adjust downward if the comp is superior (it sold for more because it has something your home does not have).

Common line items:

• Gross living area: a widely used rule of thumb is $50 to $150 per square foot depending on your market. Find out what your local assessor uses by asking at the office or looking in the assessor's published mass appraisal model documentation, which many counties post publicly.
• Garage: in most Midwest and Sun Belt markets, an attached two-car garage adds $15,000 to $25,000. A detached garage adds less.
• Bathrooms: a full bath typically adds $5,000 to $15,000 in most markets. A half bath, less.
• Lot size: in urban areas, marginal lot size often contributes very little above a base. In suburban and rural markets, extra acreage can be significant.
• Condition: this is the hardest to quantify without a licensed appraisal. If you're appealing because your home has deferred maintenance or a defect, photograph it and describe it, rather than trying to put an exact number on the condition adjustment.

Your final adjusted values across the comps should cluster reasonably close together. If one adjusted comp lands at $280,000, one at $295,000, and one at $288,000, the indication of market value is in that range. If one lands at $220,000 and the other two at $290,000, the $220,000 comp probably has an issue with selection or adjustment, and a sharp hearing officer will ask about it.

A simple one-page grid showing your address at the top, each comp's address and sale price, the adjustments, and the adjusted value is enough for an informal appeal. Our DIY property tax appeal kit at TaxFightBack includes a pre-built grid template so you're not formatting a spreadsheet from scratch.

What is the difference between comparable home sales and the assessor's model?

The assessor almost certainly used sales data to build the assessed value you're fighting. So why do your comps sometimes point to a different number?

Mass appraisal models apply broad neighborhood factors and regression coefficients across hundreds or thousands of properties at once ^[1]. They are statistically valid at the aggregate level. At the individual property level, they can be off by a lot because they rely on property characteristic data that may be wrong, outdated, or incomplete. Common errors include:

• Wrong square footage (if the assessor's field data from a prior decade doesn't match what was actually built)
• Missing or miscoded depreciation for age, condition, or functional obsolescence
• Misclassified quality grade (the assessor may have coded your home as "average plus" when it's truly "average")
• Neighborhood boundary misassignment (your home may be coded into a higher-value neighborhood cluster than it actually occupies)

Your comps don't need to explain why the model was wrong. They just need to show that the market says your home is worth less. The board's job is then to decide whether the assessor's model or the market evidence is more persuasive. Three well-selected, well-adjusted comps almost always carry weight even without an explanation of what went wrong in the model.

The International Association of Assessing Officers (IAAO), which sets the professional standard for mass appraisal, calls for a coefficient of dispersion (COD) of no more than 15% in residential areas, meaning no more than 15% average deviation between assessed and market values ^[7]. In many counties, actual performance is worse than that for individual properties, which is exactly why individual appeals succeed.

How to find comparable homes for sale versus sold, and why only sold matters

Active listings, homes currently for sale, are not comps. A listing price is an asking price. It tells you what a seller hopes to get. It does not tell you what a buyer paid.

Assessment law in every state ties value to actual transactions. The Uniform Standards of Professional Appraisal Practice says the same: "The sales comparison approach is based on data from actual sales" ^[2]. An assessor or hearing officer will not accept active listings as evidence of market value, and if you bring them, you'll lose credibility for the comps you do have.

That said, active listings in your neighborhood are useful for one specific purpose: they help you confirm that the market hasn't risen sharply after your valuation date in a way that would undercut your argument. If current listings are all priced at $400,000 and your assessed value is $320,000, that's actually a problem for your appeal. Your goal is to show the assessor's value is too high, so you want sold comps below the assessment, and you want to make sure the current market doesn't contradict that narrative.

Pending sales (under contract but not yet closed) are a gray area. They are evidence the market accepted a certain price, but the final number may differ from the contract price. Use them only if you have no better options, and note the status clearly.

Searching for "comparable homes for sale in my area" is how most homeowners start, and it's fine as a first look at neighborhood price ranges. Just make sure you pivot to sold data before you build your actual evidence package.

Can you use Zillow or Redfin data in a formal appeal?

Yes, with some preparation. Zillow and Redfin pull their sold data from county recorder feeds and MLS systems, which are the same sources a certified appraiser uses. The sale prices are real. The question is whether the hearing officer will treat a Zillow printout as credible documentation.

For informal appeals (the first level of most state appeal processes, usually a meeting with an assessor's staff or an informal review), Zillow printouts with sale date, address, price, and a photo of each comp work fine in most jurisdictions. Print the page that shows the sold date and price clearly. If the site shows the property's bed/bath/square footage, include that too.

For formal hearings before an appraisal review board or a Board of Equalization, the standard rises. You want documentation that can be tied back to public record. The cleanest approach is: 1. Find the comps on Zillow or Redfin to identify candidate sales. 2. Verify each sale in the county assessor's or recorder's public database. 3. Print the county's own record of the sale as your formal exhibit.

That way, your evidence cites the county's own data, which is hard to dispute.

For counties with less searchable systems, like some rural counties or smaller jurisdictions in the South and Midwest, you may need to pull actual deed transfer records from the county clerk. Many county clerks have online search portals now. If yours doesn't, a trip to the courthouse is worth it for a case involving thousands of dollars.

Cherokee County and Gwinnett County in Georgia, for example, both have searchable sales databases through their tax assessor portals. See our guides on the Cherokee County tax assessor and Gwinnett County tax assessor for the specific search tools available in each county.

What if there are no comparable sales near your home?

This happens in rural areas, in unusual housing markets, or for distinctive properties. It's genuinely harder to win a sales comparison argument without comps, but it's not hopeless.

Your options:

Expand the radius. If there are no comps within a mile, try two miles, then five. Rural appraisers do this routinely. Just be prepared to explain why the expanded comps are appropriate (similar market, similar land characteristics, comparable amenities).

Expand the time window carefully. If the market has been flat or declining, sales from 18 to 24 months ago may still be relevant. The risk is that the assessor argues the market rose after those sales. If you go beyond 12 months, include FHFA price index data to show the market was flat or declining during the intervening period ^[5].

Use the income or cost approach. For a single-family home with no good comps, the cost approach (land value plus depreciated replacement cost of improvements) is sometimes the only alternative. It's harder to build as a DIY filer, but county assessors are required in most states to consider all three approaches to value. If you can show the assessor's cost approach is internally inconsistent, that's an argument.

Request the assessor's own comps. In most states, you have a right to see the sales evidence the assessor used to value your property. Ask for it. If the assessor used comps from a different neighborhood or with significant unadjusted differences, that's your argument: their comps are worse than yours.

In Texas, for example, the property owner's right to inspect the appraisal district's evidence before the hearing is written into the Texas Tax Code, Section 41.461 ^[8]. Many other states have similar disclosure requirements. Knowing the assessor's comps going into the hearing is a real advantage.

How to organize and present your comps at a hearing

Organization signals credibility. A hearing officer or appraisal review board sees dozens of cases in a day. The filer who hands over a clean, one-to-two page summary with clearly labeled exhibits gets more serious consideration than the one who hands over a folder of browser printouts.

A workable format:

Cover page: Your property address, the assessed value you're contesting, the value you believe is correct, and the date.

Adjustment grid: A table with one column for your property (the subject) and one column per comp. Rows cover sale price, sale date, distance, GLA, lot size, beds, baths, garage, condition, each adjustment, and the adjusted value. The bottom row shows the adjusted comparable sale price for each comp.

Exhibits: One page per comp. Include the property address, a photo (even a Google Street View screenshot is fine for informal hearings), the sale date, the sale price, and the source (county record, Zillow sold, etc.).

Conclusion: One sentence stating the indicated value from your comps, and one sentence comparing that to the assessed value.

Keep everything to under 10 pages for an informal appeal. For a formal ARB (appraisal review board) hearing in Texas or a Board of Equalization hearing in California, you may go longer if the evidence warrants it, but a concise submission is almost always more effective.

Bring three copies: one for the board, one for the assessor's representative, and one for yourself to follow along. Some boards scan submissions electronically, but having physical copies avoids delays.

For specific county hearing procedures in larger metro areas, see our guides on San Diego property tax and Cook County tax assessor tax bill appeals, which have detailed local procedures.

Common mistakes that get comp-based appeals dismissed

The appeal with three good comps can still fail. Here's what actually sinks these cases.

Using active listings instead of sold sales. Covered above, but worth repeating because it's the most common mistake. Listings are hopes; sales are evidence.

Ignoring the valuation date. If your comps all sold after a market run-up that happened after the assessor's valuation date, the board may accept those sales but then say the value is supported. Know the exact valuation date in your state and select accordingly.

Cherry-picking the lowest sales without explaining differences. Boards are not naive. If all three of your comps are distressed sales or have significant features your home lacks, the assessor's representative will point that out. Your comp set should be explainable and honest.

Skipping adjustments. A comp that sold for $30,000 less because it's 400 square feet smaller does not mean your home is worth $30,000 less than assessed. It might mean the assessment is exactly right. You have to do the math.

Failing to verify the comp's actual characteristics. Zillow sometimes has incorrect square footage or bedroom counts due to data errors. If you base an adjustment on a wrong number, the assessor's representative may catch it and undermine your whole presentation. Always verify size and characteristics against the county assessor's own property record card.

Missing the deadline. None of the comp work matters if you filed late. Appeal deadlines range from 30 days to 90 days after your assessment notice, depending on state and county ^[9]. Miss the window and you wait another year.

Madison County and Bibb County in Georgia, for example, both have relatively tight informal appeal windows. Check the specific deadlines at the Madison County tax assessor and Bibb County tax assessor sites before you do any comp research.

Does a lower assessed value actually lower your tax bill by the same percentage?

Not necessarily, and understanding this prevents frustration after a successful appeal.

Your property tax bill is: (assessed value x assessment ratio x tax rate) minus any exemptions.

The assessment ratio is how much of the market value your state taxes. Some states tax 100% of market value. Others tax a fraction. Alabama, for example, assesses residential property at 10% of market value before applying the millage rate ^[10]. Texas assesses at 100% of market value but caps how much the assessed value can rise in a single year for homestead properties.

If your county uses a partial assessment ratio, a reduction in market value produces a proportional reduction in the assessed value portion, and then that smaller number gets multiplied by the tax rate. The result is a lower bill, but not necessarily by the dollar amount you'd calculate if you assumed 100% assessment.

Exemptions stack on top of the value reduction. If you have a homestead exemption of $25,000 and you get the assessed value reduced by $20,000, the net taxable value after exemption changes, but the math depends on the order of operations your state uses. Some states apply the exemption to the assessed value before multiplying by the ratio; others apply it after.

The short version: always verify your state's specific formula with the county assessor's office or your state's revenue department website before you estimate your savings. A $30,000 reduction in assessed value might save you $600 per year in one state and $1,200 in another, depending on the local tax rate and ratio.

Frequently asked questions

How far back can I use comparable sales for a property tax appeal?

Most appeal boards prefer sales within 12 months of your property's valuation date. Some states accept up to 24 months if few recent sales exist. Going beyond 12 months is acceptable only if you can show the market was stable during the gap, using a price index like the FHFA House Price Index. Expand your geographic radius before expanding the time window.

Can I use Zillow comps for a property tax appeal?

Yes, for informal appeals in most jurisdictions. Zillow's sold data comes from county recorder feeds and MLS systems, so the sale prices are real. For formal hearings, verify each Zillow comp against the county's own public database and use the county record as your primary exhibit. That way your evidence is the assessor's own data, which is difficult to dispute.

How many comparable sales do I need to win a property tax appeal?

Three well-selected, well-adjusted comps is the practical minimum. Five to six is stronger. More than eight adds diminishing returns for a residential appeal unless you're building a statistical argument. Each comp should be an arms-length sale of a similar home within a reasonable distance and time window from your property's valuation date.

What is the valuation date, and why does it matter for choosing comps?

The valuation date (also called assessment date or lien date) is the specific point in time your assessor used to estimate your home's value. It varies by state, often January 1 of the tax year. Your comps must reflect market conditions on that date, not today. If the market has risen since then, current comps may actually hurt your case.

Should I hire an appraiser to get comps, or can I do it myself?

For informal appeals, you can absolutely build your own comp grid from free public sources. A licensed appraisal costs $300 to $600 or more and is generally not worth the cost for an informal hearing. For a formal appraisal review board or state tax court hearing involving a large assessment difference, a certified appraisal carries more weight and may justify the expense.

What is an arms-length sale, and why do non-arms-length sales get rejected as comps?

An arms-length sale is a transaction between a willing, unrelated buyer and seller with no duress. Foreclosure sales, short sales, estate sales, and transactions between relatives are typically non-arms-length. They sell at prices that don't reflect normal market conditions. Hearing officers and boards will discount or reject non-arms-length comps because they don't represent what a typical buyer would pay.

How do I find the square footage of comparable homes to verify what Zillow shows?

Use your county assessor's property search. Every assessed property has a record card showing the gross living area (GLA), year built, bedroom and bathroom count, and sometimes a sketch of the floor plan. This is the data the assessor used to value the property. If Zillow's number and the county's number disagree, use the county's number and note the discrepancy in your adjustment grid.

My neighborhood has very few sales. Can I still use the sales comparison approach?

Yes, but you may need to expand your radius or time window. For rural areas, sales three to five miles away from a truly comparable neighborhood are acceptable. If you go beyond 12 months, use the FHFA House Price Index to document that prices were stable or falling during the gap. If no adequate comps exist, you can supplement with a cost-approach argument or challenge the assessor's own comps.

Does a successful appeal lower my property tax by exactly the same percentage as the value reduction?

Not always. Your bill depends on the assessed value, the assessment ratio (which varies by state), and the tax rate. Some states assess at less than 100% of market value. Exemptions also affect the final taxable value. A $25,000 reduction in market value produces different dollar savings depending on your local rate and ratio. Verify your state's specific formula with the county assessor's office.

Can I use the assessor's own comparable sales against them?

Yes, and this is often highly effective. In most states, including Texas under Tax Code Section 41.461, you have the right to inspect the appraisal district's evidence before your hearing. If the assessor used comps from a different neighborhood, comps with significant unadjusted differences, or sales that were not arms-length, pointing that out is a powerful argument. Request the assessor's evidence package as soon as possible after filing your appeal.

How do I adjust for condition differences when my home is in worse condition than the comps?

Condition adjustments are the hardest to quantify without a license. The most credible approach for a DIY appeal is to document the condition issue with photographs and a written description, then argue that the adjusted value of your comps should be reduced accordingly. If you have a repair estimate, that number provides a concrete basis for the adjustment. Alternatively, find comps in similar condition to your home so no condition adjustment is needed.

What is the IAAO standard, and why does it matter for my appeal?

The International Association of Assessing Officers sets professional standards for mass appraisal. Their standard calls for a coefficient of dispersion (COD) of no more than 15% in residential areas, meaning the average deviation between assessed and market values should not exceed 15%. If your county's assessments consistently overshoot market value by more than that, individual appeals become easier to win. Some states require assessors to meet IAAO standards by statute.

How do I find comparable home sales in my area for free?

Start with your county assessor's public sales database, which most counties post online. Then check Zillow and Redfin's sold listing filters, which pull from MLS and county recorder feeds. The FHFA's public House Price Index tool provides market trend data by ZIP code. For deed-level records, most county clerk websites now have searchable transfer databases. All of these are free.

What happens if the assessor disputes my comps at the hearing?

The assessor's representative may argue your comps are too far away, too old, or have unadjusted differences. Be prepared to explain your selection criteria and your adjustments. If they counter with their own comps, compare the two sets on the selection criteria: recency, distance, similarity of GLA and age. Boards generally find for the party with the more consistent, better-documented evidence package, not necessarily the party with the lower-priced comps.

Sources

1. International Association of Assessing Officers, Standard on Mass Appraisal of Real Property: County assessors use mass appraisal models that apply statistical regression to large numbers of sales simultaneously to produce assessed values
2. Appraisal Foundation, Uniform Standards of Professional Appraisal Practice (USPAP): USPAP states that the sales comparison approach is based on data from actual sales, not listing prices or asking prices
3. Fannie Mae, Single Family Selling Guide, B4-1.3-09: Comparable Sales: Arms-length sales exclude foreclosures, estate sales, and related-party transactions because they do not reflect normal market conditions
4. Cook County Assessor's Office, Property Search and Appeals: Cook County operates a triennial reassessment cycle and publishes a searchable database of sales and property characteristics
5. Federal Housing Finance Agency, House Price Index Datasets: The FHFA publishes public House Price Index data by metro area and ZIP code going back to 1991, usable to document market trends
6. California State Board of Equalization, Property Tax Rules, Rule 2 (Proposition 13): Under Proposition 13, California limits annual assessment increases to 2% except after change in ownership or new construction, making base-year value the key contested figure
7. International Association of Assessing Officers, Standard on Ratio Studies: The IAAO standard calls for a coefficient of dispersion of no more than 15% in residential areas, meaning no more than 15% average deviation between assessed and market values
8. Texas Comptroller of Public Accounts, Texas Tax Code Section 41.461: Texas Tax Code Section 41.461 gives property owners the right to inspect the appraisal district's evidence before the ARB hearing
9. National Taxpayers Union Foundation, Property Tax Appeal Deadlines by State: Property tax appeal deadlines range from 30 to 90 days after assessment notice depending on state and county
10. Alabama Department of Revenue, Property Tax Division: Alabama assesses residential property at 10% of market value before applying the millage rate
11. Los Angeles County Assessor, Property Search Portal: Los Angeles County Assessor publishes a public portal with sale price, sale date, and property characteristics available by address search
12. Maricopa County Assessor, Property Search: Maricopa County Assessor provides a searchable property and sales database for comparable sales research