How to find comparable sales comps for a property tax appeal

Last updated 2026-07-09

Why are comparable sales the strongest evidence in a property tax appeal?

Comparable sales win appeals because they speak the assessor's own language. Every U.S. state requires property to be valued at or near fair market value, and nearly every state statute defines that as the price a willing buyer would pay a willing seller in an arm's-length transaction. A recorded sale is exactly that. Show three or four genuine sales of houses almost identical to yours that closed below your assessed value, and you're not arguing. You're pointing at the county's own data.

Random appraisal error is normal. The International Association of Assessing Officers (IAAO), the body that sets mass appraisal standards, treats a coefficient of dispersion (COD) below 15 as acceptable for residential property in most markets ^[1]. Plain English: sale prices and assessed values can differ by about 15 percent on average before anyone flags a problem. Plenty of counties run higher than that. Which means a real share of homeowners sit over-assessed at any moment, and they never check.

Comps give a hearing officer something concrete to rule on. Opinion testimony is weak. Neighborhood complaints are weaker. A contractor's repair estimate barely moves the needle. A sale recorded in the county deed office is a fact. Build your case on facts and let the assessor be the one scrambling.

What time period should your comps cover?

Your comps have to bracket the assessment date, not your hearing date or the day you mail the appeal. Every state sets an "assessment date" or "lien date," the single day the assessor is supposed to estimate your value. Miss that anchor and even great sales get discounted.

Most states use January 1 of the tax year. California uses January 1 ^[2]. Texas assessors value property as of January 1 ^[4]. New York City runs a July 1 to June 30 fiscal year with a January 5 taxable status date ^[3]. Read your notice of appraised value. It names the date.

From that date, work backward 12 months as your default. Some appeal boards allow 18 to 24 months when the market was thin, and Illinois formally allows a 24-month look-back for residential property. Going too far back hurts you in a rising market and can get comps tossed in a falling one. Start with the 12-month window. Expand only when you have to.

Sales after the assessment date are tricky. They reflect a market that didn't exist yet on the valuation date. Many boards still accept them as corroboration, especially when prices were flat or falling. Don't lead with them. Keep them as backup.

Where can you actually find comparable sales data for free?

Five free sources do the job, and you should cross-check at least two of them before you cite a single number.

County assessor or auditor website. First stop. Most assessors run a public property search portal where you look up any parcel by address and see the sales history attached to it. Search by subdivision, street, or map/block/lot, then filter by sale date. Counties that publish this cleanly include Cook County, IL ^[5], Los Angeles County, CA ^[6], and Bexar County, TX ^[7]. If the portal exports a CSV, take it. Sorting in a spreadsheet beats clicking through parcels one at a time. Our guides to the cook county tax assessor tax bill and los angeles county property tax walk through those specific searches.

State deed or transfer tax records. Many states require the sale price on the deed or on a transfer tax form filed at closing, and those are public record. In Georgia, the PT-61 real estate transfer tax form goes with every deed and lists the price ^[8]. Pennsylvania files a similar realty transfer statement. Search your county recorder or register of deeds for "deed transfers" by date range.

Zillow, Redfin, and Realtor.com sold listings. These aggregate MLS data in states where disclosure is common. Filter to "sold," set the date range, draw a radius around your house, and export the results. The data holds up for suburban single-family homes. It lags or drops out for rural counties and dense urban condos. Verify every Zillow price against the county record before you cite it. Discrepancies happen more than you'd think.

Your state's real estate or property appraiser portal. Some states run a statewide sales database. Florida's county property appraiser sites pull straight from deed records and are close to complete ^[9].

FHFA House Price Index. This won't hand you individual comps, but it argues market direction when the assessor leaned on a stale base year. The Federal Housing Finance Agency publishes quarterly house price indexes by metro area ^[10]. If prices in your metro fell 8 percent between the assessment date and the hearing, that index is admissible context.

How similar does a comp have to be to be useful?

Appeal boards judge comparability on five factors, and the tighter your comps score across all five, the harder they are to wave off. Location, sale date, gross living area, lot size, and condition. Nail those and the assessor has little room to argue.

Factor	Ideal range	What weakens the comp
Location	Same subdivision or within 0.5 miles	Different school district, busy road, flood zone
Sale date	Within 12 months of assessment date	More than 24 months prior
Gross living area (GLA)	Within 10-15% of subject	More than 20% smaller or larger
Lot size	Within 20-25%	Dramatically larger corner lot, lake frontage
Condition/age	Similar condition, within 10 years of age	Major remodel on comp, distressed sale

A comp that differs on one factor still works if you own the difference and adjust for it. Say your house is 1,400 square feet and your best comp is 1,600. Note the comp's price per square foot, apply that rate to the size gap, and show the adjusted value still lands below your assessment. Boards respect honest math. Pretending a comp is identical when it isn't makes the whole packet look shaky.

Condition matters more than most homeowners expect. A comp that sold right after a full kitchen renovation, in a street of untouched homes, is not comparable to your untouched house. Pull the permit history on any comp you're weighing. Most counties post permits online. A $40,000 permitted addition in the last three years? Set that comp aside.

How many comps do you need?

Three is the practical floor. Five is comfortable. More than seven starts to read like you're papering over weak individual comps.

The assessor's office used at least three to five sales to set your value. Match that floor. Three comps all pointing the same way, all within half a mile, all recent, all showing a value meaningfully below your assessment, is a clean case. Add two more for margin against the assessor claiming one of your three isn't really comparable.

Condos and townhomes in bigger buildings are the easy mode. You can often find ten or more sales in your exact building inside the window. Use the building's own sales as your primary evidence. They're the tightest comps that exist. An assessor arguing that two units on the same floor of the same building aren't comparable has almost nothing to stand on.

Rural or unusual properties are the hard mode. Three comps may be impossible. Expand the radius to two or three miles, stretch the window to 18 months, and state plainly in your submission that you searched within half a mile and found no qualifying sales. Acknowledge the imperfect comparables and explain your adjustments. Boards know rural markets are thin, and they respect a documented search.

How do you calculate value from your comps once you have them?

Start with price per square foot. Take each comp's recorded sale price, divide by its gross living area, and note the per-square-foot rate. Multiply by your home's GLA. If your three comps average $185 per square foot and your home is 1,500 square feet, the indicated market value is $277,500. If your assessed value is $320,000, you have a clean gap to argue.

That's plenty for a basic appeal. A more rigorous version, the "sales comparison grid," is what licensed appraisers use. You list each comp's sale price, then add or subtract dollar adjustments for GLA, lot size, garage, bathrooms, and condition. The adjusted prices converge on an indicated value for your property. You don't need a license to build one for your own appeal. You need to be logical and consistent.

The IAAO Standard on Ratio Studies defines a sales ratio as assessed value divided by sale price ^[1]. When your comps land 10 to 20 percent below your assessment, you're showing your ratio sits above the median for your class of property. That's textbook grounds for relief in most states.

If math isn't your thing, TaxFightBack's appeal kit includes a pre-built comp grid spreadsheet that walks you through the adjustments, so you're not rebuilding it from scratch at midnight before the deadline.

What makes a comp invalid or unusable?

Not every recorded sale is an arm's-length transaction, and hearing officers throw out the ones that aren't. They're right to. A distressed price or a deal between relatives tells you nothing about what a house is worth on the open market.

Sales to strike from your list:

Foreclosure and REO sales. A bank unloading a repossessed property takes a below-market price to clear inventory. Many state statutes explicitly exclude sheriff's sales and bank REO sales from assessment comparisons.

Related-party sales. Parent to child, sibling to sibling, business partner to partner, estate to a family member. These almost never reflect full market value.

Sales with unusual financing. If the seller carried a large second mortgage at zero percent, or the buyer assumed a below-market loan, the nominal price doesn't match what the property fetched in a normal deal.

Partial interest sales. A sale of half a property, or the land only, isn't the whole property.

Tear-down sales. If a buyer clearly paid for the dirt and demolished the house, the price reflects land, not the improved property.

Your county's sales database usually flags these as "non-qualified" or "non-arms-length." Look for a field named "qualified sale," "valid sale," or "arms-length indicator," and filter to qualified sales only before you build your set. Slip a foreclosure into your evidence and let the assessor catch it, and your credibility drops even if the rest of your comps are solid.

How do you organize and present your comps at the hearing?

Presentation carries more weight than most DIY appellants expect. A hearing officer working through thirty cases in a morning has no time to decode a printout of raw numbers. Make your argument visible in thirty seconds or lose the room.

A one-page summary sheet. Put your subject property at the top: address, parcel number, assessed value, your estimated market value. Below it, list each comp in a plain table: address, sale date, sale price, GLA, price per square foot, and any material difference from your home. In the right column, show the adjusted value your property implies from that comp. At the bottom, show the average or median indicated value. Label it clearly.

One page of backup per comp. Print the county's own property record card for each comp, or a screenshot from the assessor's portal showing sale date, sale price, and details. This matters: you want every number traceable to the county's own records. If you're citing Zillow, print the county card for that same property so the numbers match on paper.

A photo page. A picture of your property beside your lowest-priced comp, with a short note on why they're genuinely similar, helps a hearing officer who's never seen your street.

Counties like Montgomery County, MD or Gwinnett County, GA that use in-person or phone hearings expect three paper copies: one for you, one for the officer, one for the assessor's rep. Digital submissions are more common every year, so check your county's instructions. If you're before a formal board of review, ask in advance whether you can file exhibits electronically. Our guides for montgomery county property tax and gwinnett county tax assessor cover the local steps.

Do you need a licensed appraiser to find or use comps?

No. Researching public records, pulling sale prices, and presenting that data at an informal hearing or an appeal board takes no license at all. Homeowners do it every day and win.

A licensed appraisal helps in three spots. First, if your property is unusual (historic, large acreage, mixed-use, or in a thin market), a professional can make adjustments you'd struggle to defend on your own. Second, if your case reaches tax court or a formal judicial review, most jurisdictions require appraisal testimony from a licensed appraiser to establish value. Third, if the dollar amount at stake is big, a $400 to $800 residential appraisal can pay for itself many times over.

For a typical residential appeal where the assessed value is $20,000 to $80,000 too high, clean DIY comps are usually enough. Most informal hearings wrap in 15 to 30 minutes. Officers have seen enough cases to recognize when three tight comps tell a straight story.

If you do hire someone, confirm they're licensed in your state (check the Association of Appraiser Regulatory Officials, AARO, or your state appraisal board) and tell them you need a "retrospective appraisal" with an effective date matching the assessment date, not today ^[11]. Skip that step and you've paid for the wrong document.

What if the assessor pushes back on your comps at the hearing?

The assessor will often bring their own comps showing higher sales. That's normal. Your job isn't to win every point. It's to show your comps are at least as valid as theirs.

Common pushbacks, and how to handle them:

"That sale is outside our standard search area." Ask what their standard area is. If your market genuinely lacks sales inside that radius, expand and explain why. If they're using an artificially tight radius to shut out your evidence, note that comparable means similar, not necessarily nearby, and that IAAO guidance supports widening the radius when local sales are scarce ^[1].

"That comp is in worse condition than your house." Ask how they know. If they never inspected your house, the condition assumption is a guess. If your house needs a roof or has deferred maintenance, say so and show photos.

"We used a different time period." Ask what assessment date they used and what sales window they drew from. If they leaned on a period when prices ran higher, point to the FHFA index or your state's market data showing the change ^[10].

"The sales you're citing are non-qualified." A fair objection. If you let a foreclosure or related-party sale slip in, concede it and fall back on your remaining comps. This is exactly why you brought five, not three.

Stay calm and factual. Getting adversarial with a hearing officer burns goodwill you can't spare.

Are there state-specific rules about what sales data you can use?

Yes, and the variations change your whole strategy.

California is its own animal. Under Proposition 13, assessed values are capped at 1 percent of the 1975-76 base year value plus up to 2 percent a year, and they reset to market value only on a change of ownership or new construction ^[2]. California appeals usually turn on whether current market value has dropped below the Prop 13 base, not on sales-ratio equity. Comps still matter, but the legal theory is different. The Santa Clara County Assessment Appeals Board is a good model for how these hearings run. Our santa clara property tax guide has the details.

New York City uses an income approach for most class 2 (rental) and class 4 (commercial) properties, so comps carry more weight for class 1 (small residential) appeals ^[3]. Appealing an NYC class 1 assessment? The NYC Department of Finance's ACRIS database is your source for deed-recorded sale prices ^[3].

Texas requires comps within the same appraisal district (usually the county) and uses a January 1 assessment date ^[4]. Texas Property Tax Code Section 41.43 governs the burden of proof at appraisal review board hearings and lets you establish value by showing the appraised value exceeds market value.

Illinois (Cook County specifically) allows a 24-month look-back for residential appeals and runs three-year reassessment cycles. The Cook County Assessor publishes comparable sales grids you can request or download, and matching their format when you submit your own evidence makes side-by-side comparison easy ^[5]. Our cook county tax assessor tax bill guide covers it.

Georgia's PT-61 transfer tax form means deed-based sale prices are reliably public ^[8]. The Gwinnett and Bibb County assessors both post sales data through their GIS portals. Our bibb county tax assessor guide shows how to pull those records.

Read your state's assessment appeal statute before you file. Find the sections on evidence standards, burden of proof, and which sale types are excluded.

What is the fastest way to pull comps if your deadline is in two weeks?

Two weeks is tight but doable. Here's the fastest path.

Day 1: Go to your county assessor's site, find the property search portal, and look up your own parcel. Note the assessment date, square footage, lot size, year built, and any special features. Then search for sales in your subdivision or zip code in the 12 months before the assessment date. Export to CSV if you can.

Day 2: Open Zillow or Redfin, filter to sold, set the date range, and search within 0.5 miles of your address. Screenshot or download the results. Cross-reference the top candidates against your county portal to verify prices.

Day 3: Cut your list to the five most similar properties. For each, pull the county property record card and note differences in size, bed/bath count, lot size, or condition.

Day 4: Build the one-page summary table described above. Calculate price per square foot for each comp. Compute your indicated value. Note the gap against your assessment.

Day 5 and beyond: Write a one-page cover letter, print your backup exhibits, assemble the packet, and file before the deadline.

The research phase runs three to five hours if your county has a good portal. If the portal is bad, budget another two to three hours on Zillow and deed-transfer records. Appeal filing deadlines vary widely, commonly 30 to 90 days from the date your assessment notice is mailed ^[12]. Miss it and you usually wait a full year for another shot. Don't.

Frequently asked questions

Can I use Zillow to find comps for a property tax appeal?

Yes, with a caveat. Zillow's sold-listings data is reliable for suburban single-family homes but has gaps for rural and urban condo markets. Verify every Zillow sale price against your county's public deed records before citing it. Presenting a comp with a wrong price wrecks your credibility. Use Zillow to find candidates, then confirm each one with the county record.

How far back can my comps be dated?

Twelve months before your assessment date is the standard window in most states. Illinois formally allows 24 months for residential appeals. Some boards accept 18-month-old sales when the market was thin. Go back further only when you have no closer sales, and explain why. Post-assessment-date sales are sometimes accepted as corroboration but shouldn't lead your case.

Do foreclosure sales count as comparable sales for a tax appeal?

Usually not. Foreclosure sales, REO (bank-owned) sales, and sheriff's sales are commonly excluded from arm's-length comparables under most state assessment statutes, because distress pricing doesn't reflect normal market value. Most county databases flag these as 'non-qualified' sales. Filter them out before building your set, or the assessor's rep will exclude them for you and weaken your case.

What if there are no comparable sales near my house in the past year?

Expand your radius to one or two miles, or stretch the window to 18 to 24 months, and state in your appeal why the standard window yielded no qualifying sales. Rural and unusual properties sometimes need a three-mile radius. Acknowledge each comp's limits and adjust for location or time. Hearing officers know thin markets are real. Document your search effort.

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

Three to five is the practical standard. Three clean, well-matched comps all pointing below your assessment is usually enough for an informal hearing. Bring five for margin in case the assessor challenges one. More than seven comps without strong individual quality reads like you're covering for weak evidence. Quality beats quantity every time.

Can I use a pending sale as a comp?

No. A pending or contingent sale hasn't closed, so no price is recorded and no deed has transferred. It isn't usable as a comparable. Only closed, recorded arm's-length transactions count. If a sale you know about closes before your hearing, you can add it then, but verify the recorded price through the county deed office first.

What is the difference between a comp and a CMA?

A CMA (comparative market analysis) is an informal value estimate agents prepare for buyers or sellers, built on recently sold comps. It isn't a licensed appraisal. For a tax appeal, you can use the underlying sales data from a CMA, but the CMA document itself carries no special evidentiary weight. The recorded sale prices are what matter, not the agent's packaging around them.

Does the assessor use the same comps I do?

The assessor uses mass appraisal, which calibrates assessed values across thousands of properties at once with sales ratios and regression models, not individual comp grids. You can often request the sales ratio study or the sales used for your neighborhood, and in many states that's public record. Seeing the assessor's data shows which comps they relied on and whether any were non-qualified sales or outliers.

Is a licensed appraisal required to appeal a property tax assessment?

For informal hearings and most state board-of-review appeals, no license is required. You can present your own comps. A licensed appraisal is typically required only if your case reaches tax court or a formal judicial proceeding. Since most residential appeals settle at the informal or board level, a full appraisal is optional and worth the cost mainly when the stakes are large or the property is unusual.

How do I adjust for differences between my property and a comp?

Calculate each comp's price per square foot, then apply dollar adjustments for size, lot, condition, and features. If a 1,600-square-foot comp sold at $200 per square foot and your home is 1,400 square feet with no garage (the comp had one), subtract a garage adjustment and multiply the per-square-foot rate by your GLA. Logical, documented adjustments make your case stronger. Unexplained assumptions make it weaker.

What if the assessor brings different comps to the hearing that show a higher value?

Examine their comps on the spot. Check whether the sale dates fall in the valid window, whether the properties are genuinely similar in size and condition, and whether any are non-arm's-length transactions. Point out any differences plainly. The hearing officer weighs both sets. Your goal is to show your comps are at least as credible as theirs, not that theirs are fraudulent.

Can renters use comparable sales to appeal a property tax assessment?

Renters generally cannot file a property tax appeal because they aren't the owner of record. The right to appeal belongs to the owner. If you rent in a jurisdiction where your lease ties rent reductions to tax changes, your landlord's appeal outcome could affect your rent indirectly, but you cannot file the appeal yourself.

Where can I find the sales data the assessor used to value my neighborhood?

File a public records request (sometimes called a FOIA or open records request) for the sales ratio study, assessment roll, or comparable sales grid used in your neighborhood's last revaluation. Most states require assessors to keep these and make them available. Your county assessor's website may also post annual sales ratio reports. This data shows exactly what market evidence the assessor relied on.

How do I find comps for a condo in a large building?

Search your county's sales records filtered to your building's address or parcel number range. Sales of other units in the same building are your best comps because they erase location and structure differences. Filter for similar floors, square footage, and condition. Ten or more sales in a large building over 24 months is often achievable in urban markets, giving you evidence the assessor can't easily dismiss.

Sources

1. International Association of Assessing Officers (IAAO), Standard on Ratio Studies: IAAO treats a coefficient of dispersion (COD) below 15 as acceptable for residential property, and defines the sales ratio as assessed value divided by sale price.
2. California State Board of Equalization, Proposition 13 Overview: California's Proposition 13 caps assessed values at 1 percent of base year value plus up to 2 percent annual increase, resetting at sale or new construction; assessment date is January 1.
3. Texas Comptroller of Public Accounts, Property Tax Code Section 41.43: Texas Property Tax Code Section 41.43 governs burden of proof at appraisal review board hearings; assessment date is January 1.
4. Cook County Assessor's Office, Property Search Portal: Cook County Assessor publishes comparable sales grids and allows a 24-month look-back window for residential appeals under Illinois law.
5. Los Angeles County Assessor, Public Records Search: Los Angeles County Assessor maintains a public property search portal with sales history for all parcels.
6. Bexar County Appraisal District, Property Search: Bexar County Appraisal District publishes property records and sales data online for public lookup.
7. Georgia Department of Revenue, PT-61 Real Estate Transfer Tax Form: Georgia requires a PT-61 real estate transfer tax form filed with every deed, disclosing the sale price as public record.
8. Florida Department of Revenue, Property Tax Oversight Program: Florida county property appraiser sites pull deed-recorded sale prices directly, providing near-complete public sales data for comparable sales research.
9. Federal Housing Finance Agency (FHFA), House Price Index: FHFA publishes quarterly house price indexes by metropolitan area, usable as market direction evidence in property tax appeals.
10. Association of Appraiser Regulatory Officials (AARO), State Appraisal Board Directory: AARO maintains a directory of state appraisal licensing boards for verifying appraiser credentials; retrospective appraisals must use an effective date matching the assessment date.
11. Lincoln Institute of Land Policy, 50-State Property Tax Data: Property tax appeal deadlines vary by state, commonly ranging from 30 to 90 days from the date the assessment notice is mailed.