How to find the comparable sales your assessor used to value your home

Last updated 2026-07-09

What are comparable sales and why does the assessor use them?

Comparable sales, called comps, are recent arm's-length sales of homes similar to yours. Most states require assessors to value residential property using the sales comparison approach. The assessor finds homes that sold near yours, adjusts for differences in size, age, condition, and location, and lands on a value for your home. ^[1]

The theory is sound. If three similar houses on your street sold for $280,000 last year, yours is probably worth around $280,000 too. The problem is that "similar" is doing a lot of work in that sentence. An assessor grinding through thousands of parcels may grab comps from a wider area than makes sense, or lean on sales from a period when the market ran hotter than it does now.

Figuring out which comps the assessor actually used, and whether they hold up, is the single most useful thing you can do before you file. Everything else you bring (photos, contractor estimates, a story about deferred maintenance) hits harder when it's tied to a direct rebuttal of the assessor's own comp set.

Where does the assessor publish the comps they used on your property?

Start with the assessment notice in your hand. Many counties, including Cook County in Illinois and most California counties, attach the sales they used or point you to a parcel number you can look up. ^[2] Plenty of notices are just a one-page form with a value and nothing else. That's normal, and you have other ways in.

The assessor's online property portal is usually the fastest. Search your parcel number or address, then look for tabs labeled "Sales History," "Comparable Sales," "Valuation Details," or "Mass Appraisal Data." Larger jurisdictions like Los Angeles County and Montgomery County, Maryland post detailed property cards online with the comp sales the system used. ^[3][12]

No comps on the portal? File a public records request. In every state, property valuation records are public. Under your state's open-records law (sometimes called a sunshine law or public records act), ask for the assessor's "property record card," "appraisal worksheet," or "CAMA data" for your parcel. CAMA stands for Computer-Assisted Mass Appraisal, and the CAMA record lists the comparable sales the system pulled. ^[4] Some offices answer in days. Some take weeks. Get this document before your appeal deadline either way.

For large urban counties, here's where to start:

• Cook County: the Assessor's property search at cookcountyassessor.com shows your mailed value and links to comparable properties used. Our guide to the cook county tax assessor tax bill walks through the whole thing.
• LA County: the Assessor's portal at assessor.lacounty.gov lets you search by AIN and pull the property characteristics behind your valuation. Our los angeles county property tax article covers the appeal timeline there.
• Bexar County: search bcad.org for your property and request the appraisal detail. The bexar county tax assessor article has step-by-step instructions.
• Gwinnett County: the Board of Assessors portal at gwinnettassessor.com includes property cards. See our gwinnett county tax assessor guide for the local rules.

How do I find the same sales data the assessor pulled, on my own?

Once you know which sales the assessor used, pull the underlying data yourself. You want to confirm each sale is what the assessor says it is, then hunt for sales the assessor missed or ignored.

Four free sources get you there:

County deed and transfer records. Every county records the deed when a property sells, and that document is public. Search your county recorder or register of deeds site by address. The deed gives you the grantor, grantee, date, and usually the price (though a handful of non-disclosure states don't require the price on the deed). ^[5]

County property portals. Many assessors put a "sales search" tool right on the site. Filter by neighborhood, date range, and property type. This is often the cleanest source, because the assessor's own system generated your assessment in the first place.

Zillow, Redfin, and Realtor.com sold listings. These aggregate MLS data and show sold prices with photos and square footage. Less authoritative than a deed, but fast, and the photos matter when you're arguing a comp had a remodeled kitchen your home doesn't.

Your state's real estate transfer tax database. States that collect a transfer tax, like New York and Pennsylvania, often publish a statewide transaction database searchable by county and date. ^[6] New York City's ACRIS system lets you search every recorded sale by borough, address, or block and lot.

One honest caveat. In non-disclosure states (as of 2025, roughly 12 of them, including Texas, Utah, and Wyoming), sale prices aren't public record and don't appear on the deed. ^[5] There you'll lean more on the assessor's own published sales data and on sites like Zillow, which get prices from MLS feeds rather than deeds.

What makes a comp truly comparable, and what disqualifies one?

This is where most DIY appeals fall apart. People find a cheap sale nearby and assume it wins the argument. It usually doesn't. Assessors are trained to throw out sales that aren't arm's-length, and appeal boards know the criteria cold.

A valid comp generally has to clear these tests:

Factor	Ideal range	Why it matters
Sale date	Within 12 months of assessment date	Markets shift; older sales may not reflect current value
Distance	Under 1 mile (less in dense urban areas)	Neighborhoods have micro-market differences
Gross living area (GLA)	Within 15-20% of your home's GLA	Size drives value; large gaps need large adjustments
Age of construction	Within 10-15 years	Older homes carry different maintenance profiles
Lot size	Similar, especially in suburban/rural areas	Lot premium can be big
Condition	Similar (good vs. fair vs. poor)	Often the strongest argument you have
Sale type	Arm's-length only	Exclude foreclosures, family transfers, estate sales

Sales that aren't arm's-length (buyer and seller were related, or one side was under duress) are supposed to be excluded. If an assessor comped your home against a foreclosure or a sale between relatives, that's a direct line of attack. Look for deeds where grantor and grantee share a last name, or where the price is oddly low. Both are telltale signs of a non-arm's-length transfer.

Condition is the factor homeowners can document most easily. A CAMA system assigns a rating like "Good," "Average," or "Fair" based on the last physical inspection, which in many counties happened years ago. Say your roof is shot, your HVAC is 25 years old, and the bathrooms haven't changed since 1987, but the CAMA record still reads "Good." That's a condition argument comps alone can't make. Pair your comp analysis with photos and contractor repair estimates.

How do I build my own comp grid to challenge the assessor's value?

A comp grid is a simple table that puts your home and each comparable sale side by side, lists their characteristics, and shows adjustments for the differences. Assessors and appraisers use the same format. Present yours this way and you signal you know what you're doing.

Here's the process:

1. List the assessor's comps in a spreadsheet. Pull the sale price, date, address, GLA, lot size, age, and condition rating for each. You get these from the assessor's property cards or CAMA data.

2. Find your own comps. Search the county's sales database for arm's-length sales of similar homes that closed within the last 12 months (or whatever period the assessor used; check the assessment date on your notice). Aim for 3 to 6. If the assessor's comps are all bigger or nicer than yours, finding smaller, less-updated sales is the whole point.

3. Make adjustments. For each difference between a comp and your home, apply a dollar or percentage adjustment. If a comp has an extra bathroom, you subtract value from the comp (your home would sell for less). If a comp is 200 square feet smaller, you add value to the comp. The Uniform Standards of Professional Appraisal Practice (USPAP) guide professional appraisers here, but for an appeal you can use the assessor's own adjustment schedule (some counties publish it) or derive adjustments from paired sales analysis: find two sales that differ only in the feature you're adjusting for. ^[7]

4. Reconcile to a value. Average or weight your adjusted comp values. If your reconciled number sits meaningfully below the assessor's, say 5% or more, you have a case. Below 5% is noise. Most boards won't move for that.

Want a template you don't have to build from scratch? The TaxFightBack DIY appeal kit includes a ready comp grid with adjustment guidelines tied to your state's appeal standards.

Markets have local wrinkles. In Hennepin County, Minnesota, the assessor's sales ratio studies are public and can show whether your property class is being over-assessed across the board. See our hennepin county property tax article for the details.

What time period should comparable sales come from?

This trips people up constantly. The right sales aren't always the most recent ones. They're the sales inside the assessor's valuation date window. ^[1]

Every assessment has a "valuation date" (sometimes called the "lien date" or "assessment date"), a fixed point in time. In most states it's January 1 of the tax year. Your assessor was supposed to value your home as of that date, using sales from the run-up to it, usually the prior 12 months, though some states stretch to 18 or 24 when sales are thin.

If your valuation date is January 1, 2025, the assessor's comps should be sales that closed roughly between January 1 and December 31, 2024. Sales from early 2025 or late 2023 can be used if the assessor can justify them, but you're entitled to know the exact window.

Why does this matter? If the market softened after the valuation date, recent sales look lower, but the assessor won't necessarily accept them because they postdate the valuation. Flip it: if the market was already cooling before the valuation date, the assessor should have caught it in the comp selection. Check the date on every comp the assessor used. Any that fall outside the proper window are arguable.

Some states spell out the sales window by statute. California is its own animal. Under Proposition 13, assessed value ties to acquisition value rather than annual market value, so the comp analysis works differently there. ^[8] For most other states, the International Association of Assessing Officers (IAAO) Standard on Ratio Studies recommends sales from a 12-month period centered on the valuation date. ^[9]

Can I get the assessor's full sales data file, more than just my property's comps?

Yes, and almost nobody does it. Many county assessors publish bulk data downloads of all property sales, often in CSV or Excel. That lets you run your own analysis across a whole neighborhood or property class.

Search the assessor's or county open data portal for "sales disclosure," "real property sales," "deed transfer data," or "assessment roll." Some counties publish monthly, some annually. Several states run statewide repositories. Indiana's Gateway portal publishes county assessment data across the state. ^[10]

With a full sales file you can do something powerful: calculate your own sales ratio. A sales ratio is assessed value divided by sale price. If your assessed value is $350,000 and a truly comparable house sold for $300,000, your ratio is 1.17, meaning you're assessed 17% above market. If the median ratio for your neighborhood is 1.02, your property is out of line, and that's the argument you take to the board.

IAAO research keeps finding that uneven assessment is a bigger problem than the overall level. The IAAO Standard on Ratio Studies sets a coefficient of dispersion (COD) above 15 in urban areas or 20 in rural areas as the mark of unacceptable variability. ^[9] Show your property's ratio sitting well above the neighborhood median and you strengthen your case even when the general level is about right.

For what this looks like in a big metro, our montgomery county property tax article walks through Maryland's data tools.

What if the assessor used no comps, or I can't find which ones they used?

This happens more than you'd think, especially in low-turnover markets and rural counties where few homes sell in a year. When the assessor can't find enough recent sales, they may switch to the income approach (rare for houses) or the cost approach, which estimates what it would cost to rebuild your home and subtracts depreciation.

Can't identify the comps after checking the notice, the portal, and filing a records request? Say so plainly in your appeal. You're entitled to know the basis for your assessment. Most state appeal statutes require the assessor to hand over supporting documentation. In many states, if the assessor can't produce a methodology, the board may cut the assessment or at least shift the burden of proof.

When comps are genuinely scarce, your own analysis carries more weight. Find the few sales that exist, even 18 to 24 months old, and document why they're the best available evidence. Pair that with a cost-approach analysis using Marshall & Swift cost data or a contractor's replacement-cost estimate, adjusted for your real depreciation. It's messier than a clean comp grid, but it's legitimate, and boards see it all the time.

Texas has a rule worth knowing. Sale prices aren't public there, but the appraisal district (the Texas version of an assessor) must, under Tax Code Section 41.461, give you a copy of its evidence at least 14 days before your hearing if you request it. ^[11] That evidence includes the comps they plan to use. Request it. Every time.

What red flags in the assessor's comps most often win appeals?

The same problems show up again and again as grounds for a successful challenge. Here are the common ones, in rough order of how often they move boards.

Square footage errors. The CAMA record may list the wrong gross living area. If it says 2,100 square feet and you measure 1,850, every comp is off. Measure your home and compare. This is one of the highest-return things you can do in 30 minutes.

Condition mismatch. The assessor rated your home "Good" but the comps are genuinely updated. Photos of the aging roof, dated kitchen, and unfinished basement tell that story fast.

Comps outside your neighborhood. Assessors sometimes pull sales from a zip code that crosses a school district line, a highway, or a flood plain. Homes on the far side sell for more. Map the comps (even on Google Maps) and show they sit across a real boundary. That's a compelling visual.

Comps with bigger lots. In suburban and rural areas, a comp on a half-acre against your quarter-acre carries real value the assessor should have adjusted for. If they didn't, document it.

New construction used as a comp. New builds carry a builder premium. Comp a 1978 ranch against a 2023 new build and that premium makes your value look higher than it is.

Sale date outside the window. Comps that predate the correct sales window, especially from a peak year, are challengeable.

Any one of these, backed with data, is often enough. Two or three together make the assessor's position hard to defend.

How do I present my comp evidence at the appeal hearing?

Most residential appeal hearings are informal. You sit across a table from a hearing officer or a board panel, get 10 to 20 minutes, and make your case. Brevity wins.

Bring a one-page summary sheet showing your home's characteristics, the assessor's comps, your comps, your adjustments, and your concluded value. Behind it, attach supporting sheets: property cards for each comp, a map of their locations relative to your home, and photos of condition issues. Number every page and make three copies. One for you, one for the board, one for the assessor's rep.

Lead with the facts, not the frustration. "The assessor's three comps average 340 square feet larger than my home, and two have been fully renovated. My three comps, all within 0.4 miles and sold in the same 12-month period, average $247,000 after adjustments, against the assessed value of $295,000." That's the whole case in two sentences.

Hit a question you can't answer? Say so. "I don't have that data, but I'd be glad to submit it in writing" beats guessing. Boards respect an honest answer.

The TaxFightBack appeal kit includes a hearing-ready comp grid, a one-page summary sheet, and a checklist of what to bring, all formatted for the board's standard review. You keep 100% of any reduction you win.

For specific local boards, see our guides to the bibb county tax assessor and gwinnett county tax assessor processes in Georgia, where the format has some local requirements worth knowing before you walk in.

What free tools and databases let me pull comp data without paying for it?

You don't need a paid appraisal or a contingency firm to get good comp data. Here's the toolkit.

County assessor or recorder portals. Most counties run free searchable databases. Google "[county name] property search" or "[county name] recorder deeds search."

Zillow sold listings. Filter by "Sold" and set the date range. Zillow pulls from MLS feeds and shows photos, which matter for condition comparisons. Not a primary source, but fast for a first pass.

Redfin. Similar to Zillow with slightly more data fields shown. A Redfin sold listing usually includes days on market and original list price, both useful context.

ATTOM Data and CoreLogic. The professional data providers most appraisers use. They charge for access, though ATTOM offers some free tools on its public site. Appealing a high-value property? One month of a subscription may pay for itself.

Statewide assessment databases. Indiana, Minnesota, and several other states publish statewide parcel and sales data through open data portals. Search "[state name] open data parcels" or "[state name] property assessment data."

County GIS portals. Geographic information systems often include parcel maps with assessed values and sometimes sale prices overlaid. Handy for drawing a defensible boundary around your comp search.

One practical sequence. Start with the county assessor's sales search for the assessor's own data, cross-check on Zillow for photos and condition, then pull the actual deed from the recorder's site to confirm price and date. That three-source check catches most errors.

Frequently asked questions

How do I get the assessor to tell me exactly which sales they used to value my home?

Check your assessment notice first. If it doesn't list the comps, search the county assessor's online portal by parcel number and look for a "Comparable Sales" or "Valuation Details" tab. If that's empty, file a written public records request for your property's CAMA record or appraisal worksheet. Most assessors must respond within 5 to 30 business days depending on state law. In Texas, Tax Code 41.461 requires the appraisal district to give you its evidence at least 14 days before your hearing if you request it.

What does CAMA mean and how do I get my CAMA record?

CAMA stands for Computer-Assisted Mass Appraisal. It's the software most assessors use to store property characteristics and calculate values at scale. Your CAMA record holds your home's recorded square footage, age, condition rating, and the comparable sales the system used. Request it by name in a public records request to your assessor's office. Some counties post CAMA data online through property portals or open data downloads.

How many comparable sales do I need to build a strong appeal?

Three to six is the standard range. Professional appraisers use three comps minimum, and appeal boards expect at least that. More than six gets unwieldy and can dilute a strong argument if some comps are weaker. Quality beats quantity. Three comps clearly similar to your home in size, age, condition, and location will outperform six comps with obvious problems.

Can I use Zillow sold prices as evidence in a property tax appeal?

You can submit them, but treat them as supporting evidence, not primary evidence. The primary source is the county deed record or the assessor's own sales database. Zillow is good for two things: a fast list of recent sales, and photos that document a comp's condition. Verify the sale price against the deed record before you cite a number. Some boards will ask where your data comes from, and "Zillow" alone may draw pushback.

What is a sales ratio and how does it help my appeal?

A sales ratio is your assessed value divided by the actual sale price of a comparable property. If a nearly identical house sold for $310,000 and your assessed value is $360,000, your implied ratio is 1.16, meaning you're assessed 16% above market. Show the neighborhood median ratio is around 1.00 and that gap becomes your argument. The IAAO Standard on Ratio Studies treats a coefficient of dispersion above 15 in urban areas as a sign of unacceptable variability.

What sales are considered non-arm's-length and should be excluded?

Non-arm's-length sales are transactions where buyer and seller aren't independent parties acting on market terms. Common examples: sales between family members, foreclosure or sheriff's sales, estate sales below market, sales involving a government entity, and $1 nominal transfers of ownership. If the assessor used any of these as comps, flag it. Most state assessment standards explicitly require excluding non-arm's-length sales from comp analysis.

Does it matter if the comparable sales are in a different neighborhood?

Yes, a lot. Comps should come from your neighborhood or a demonstrably similar one. If the assessor's comps sit across a school district boundary, a highway, or a flood plain line, and homes on that side consistently sell for more, that mismatch is a legitimate challenge. Map the assessor's comps against yours with Google Maps or a county GIS tool and bring the map to your hearing. Visual proof of location differences lands well with boards.

What time period should comparable sales come from for my appeal?

Use sales from the 12 months before your assessment's valuation date, which in most states is January 1 of the tax year. For a 2025 assessment, that's roughly January through December 2024. Some assessors use 18 or 24 months when sales are thin, which is fine. The sales should reflect market conditions as of the valuation date, not the day you file. Check your notice for the valuation date before picking comps.

My state is a non-disclosure state. How do I find sale prices?

About 12 states, including Texas, Utah, Wyoming, and Idaho, don't require sale prices on recorded deeds. Your options: the assessor's own published sales data (many appraisal districts post it), MLS-sourced sites like Zillow and Redfin that get prices from broker feeds, and county transfer tax records if your state collects a transfer tax. In Texas, the appraisal district must share its evidence with you before the ARB hearing if you request it under Tax Code 41.461.

How big a difference between my value and the comps do I need to win?

Most boards won't cut an assessment for a gap under 5%. At 10% or more you have a clear case worth pursuing. Run the tax math too. A 10% reduction on a $400,000 assessment is $40,000 in assessed value, and at a 1.2% effective rate that's $480 a year. Calculate your potential savings before you sink time in. For modest-value homes in low-tax areas, the effort may not pencil out.

Can I use a recent purchase price of my own home as evidence?

Yes, and it's often your strongest piece. If you bought your home in an arm's-length deal within the past 12 to 24 months for less than the assessed value, that sale is direct market evidence of what your home is worth. Bring your closing disclosure or HUD-1 to the hearing. Most states treat a recent arm's-length purchase price as very persuasive, and some create a presumption in your favor that the assessor has to rebut.

What if the assessor's comps are accurate but my home is in worse condition than those comps?

That's a condition argument, not a comp-selection argument, and it can be just as effective. Document the gap with photos, inspection reports, and contractor repair estimates. If your CAMA record rates the home "Good" but reality is worn flooring, an aging roof, original 1970s windows, and a deferred HVAC replacement, ask the assessor to update the condition rating. Even a one-grade drop, Good to Average, can cut assessed value 5 to 15% depending on the county's depreciation schedule.

Should I hire an appraiser to find comps for me, or can I do this myself?

For most residential appeals, do it yourself. A licensed appraiser costs $400 to $800 and produces a formal report, which carries weight but often overshoots what an informal hearing needs. DIY works well when the comp story is clear: the assessor's comps are plainly larger, newer, or nicer than yours. Hire an appraiser when the money at stake is high (over $100,000 in overassessment), when you're headed to a formal court-level appeal, or when the comp picture is genuinely murky.

How do I find comparable sales in a rural area where few homes sell?

Thin markets are harder. Widen the geographic search and stretch the time window to 18 to 24 months, noting you're doing so because of limited sales. Look at the county's full sales file for the past two years and filter for similar property types. When you can't find enough true comps, the cost approach matters more: what would it cost to replace your home, minus realistic depreciation? Document depreciation with specifics like roof age, deferred maintenance, and functional obsolescence. Rural boards see this all the time.

Sources

1. International Association of Assessing Officers (IAAO), Standard on Mass Appraisal of Real Property: Most states require assessors to value residential property using the sales comparison approach, finding recent arm's-length sales of similar homes.
2. Cook County Assessor's Office, Property Search Portal: Cook County publishes comparable sales information through its online property search system linked to each parcel.
3. Los Angeles County Assessor Portal, Property Search: LA County's assessor portal lets homeowners search by AIN and pull property characteristics used in valuation.
4. International Association of Assessing Officers (IAAO), Glossary for Property Appraisal and Assessment: CAMA (Computer-Assisted Mass Appraisal) is the standard system assessors use to store property characteristics and calculate values at scale; the CAMA record lists comparable sales used.
5. National Association of Realtors, Non-Disclosure States Overview: Approximately 12 states are non-disclosure states where sale prices are not required on recorded deeds, including Texas, Utah, and Wyoming.
6. New York City Department of Finance, ACRIS (Automated City Register Information System): New York's ACRIS system lets users search all recorded sales in New York City by borough, address, or block and lot.
7. The Appraisal Foundation, Uniform Standards of Professional Appraisal Practice (USPAP): USPAP guides professional appraisers in making adjustments for differences between comparable sales and the subject property in the sales comparison approach.
8. California State Board of Equalization, Proposition 13 Overview: In California, Proposition 13 ties assessed value to acquisition value rather than annual market value, making the comparable sales analysis work differently than in most states.
9. International Association of Assessing Officers (IAAO), Standard on Ratio Studies: The IAAO Standard on Ratio Studies recommends using sales from a 12-month period centered on the valuation date; a coefficient of dispersion above 15 in urban areas or 20 in rural areas signals unacceptable assessment variability.
10. Indiana Gateway for Government Units, Local Government Property Tax Data: Indiana's Gateway portal publishes county assessment data statewide, including property sales and assessed values.
11. Texas Property Tax Code, Section 41.461, Evidence at Hearing: Texas Tax Code Section 41.461 requires the appraisal district to provide its evidence to the property owner at least 14 days before the ARB hearing upon request.
12. Montgomery County, Maryland Department of Assessment and Taxation, Property Search: Montgomery County, Maryland publishes detailed property cards online that include comparable sales used in mass appraisal.