Comparable sales report: how to build one that wins a property tax appeal

Last updated 2026-07-09

What is a comparable sales report and why does it matter for a tax appeal?

A comparable sales report is a structured document listing recent arm's-length sales of homes similar to yours, set against the value your assessor placed on your property. Sometimes it's called a comp grid or a sales comparison analysis. If those sale prices cluster below your assessed value, you have the spine of a winning appeal.

Assessors run the same logic when they set your value. The income approach and cost approach exist, but for single-family homes the sales comparison approach does most of the work. The Uniform Standards of Professional Appraisal Practice (USPAP), which most state assessment laws reference, describe an arm's-length transaction as one "between a willing buyer and a willing seller, each acting in their own best interest, with adequate exposure to the open market." ^[1] That sentence is your filter. Foreclosures, estate sales where the executor needed cash fast, and transfers between family members generally don't qualify.

Why do this yourself? Because review boards do not run on feelings. "My neighbor pays less" is not evidence unless you document it. A clean comp grid, printed and organized, tells the board you did the work. That alone puts you ahead of the homeowners who show up empty-handed.

How close do comparable sales need to be in time and distance?

Most county assessor offices prefer sales within 12 months of the assessment date, and within a half-mile to one mile for urban and suburban homes. Rural parcels sometimes need a five-mile or county-wide search because sales are simply sparse. ^[2] Those are preferences, not hard walls, but the further you stray the more you have to explain.

Time carries more weight than people expect. Say your county's assessment date is January 1, 2024. A sale from March 2022 only helps if you can show the market held steady between that sale and the assessment date. In a rising market, old comps undercut you. In a falling market, an older comp may show a higher price, which actually works in your favor.

Distance is trickier. Half a mile can cross a school district line, a flood zone boundary, or a busy arterial road, and any of those moves value. Don't just count miles. Check what the assessor calls the "neighborhood" in your record. Most county portals show the neighborhood code assigned to your parcel. Comps inside that same code carry more weight than comps from a different one. ^[3]

The table below shows the search windows most county assessor offices publish or follow in practice.

Market type	Preferred time window	Preferred distance
Dense urban (Chicago, LA, Houston)	6-12 months	0.25-0.5 miles
Suburban	12 months	0.5-1.0 miles
Small town / exurban	12-24 months	1-3 miles
Rural	Up to 36 months (with adjustment)	County-wide

When you have to go outside these windows, say so in your writeup and explain why. Boards reward that kind of transparency.

Where can you find comparable sales data for free?

You have more free sources than you probably expect, and none of them require a subscription.

Start with your county assessor's or auditor's website. Most counties now publish a searchable sales database you can filter by sale date, property class, and neighborhood. Pull every arm's-length sale in your neighborhood for the past 12 months and download or screenshot the results. ^[3]

Next is the county recorder or register of deeds, which records every deed transfer, usually with the sale price. Many counties post these online. Search for "[county name] deed search" or "[county name] real estate transfers."

Zillow, Redfin, and Realtor.com all show recent sold listings with square footage, bed and bath counts, lot size, and sale date. They pull from MLS feeds that sometimes carry errors, so treat them as a fast first draft. Cross-check every sale price against the county recorder's record before you rely on it.

The Federal Housing Finance Agency (FHFA) House Price Index gives you market-level trend data by metro area and state going back to 1991. ^[4] It won't hand you individual comps, but it tells you whether your local market rose or fell between the assessor's last valuation date and today. That's ammunition when you argue the assessment is stale.

Some states run a public Multiple Listing Service feed. Most don't. If you can't scrape together enough data online, a local agent will often pull a comp report for free in exchange for a conversation about a future listing. They're under no obligation, but many will. That MLS data is exactly what an appraiser would use.

What property characteristics must match for a comp to be valid?

The closer a comp matches your home's physical traits, the less you have to explain. Here's what carries the most weight, roughly in order.

Gross living area (GLA) drives value in most residential markets. Assessors and appraisers apply a dollars-per-square-foot adjustment for size gaps. A common range runs $30 to $100 per square foot, though high-cost metros like San Francisco or Manhattan push past $200. You don't need the exact number. Just flag any comp that's more than 15 to 20 percent larger or smaller than your home, because that gap weakens the comparison.

Age and condition matter next. A 1960s ranch and a 2005 colonial in the same subdivision are not strong comps for each other. If you've never touched your kitchen or bathrooms, steer clear of comps with recent gut renovations. The assessor will spot the difference.

Lot size matters for single-family homes on large parcels, less so for row houses or condos where the land is shared. Garage type, basement finish, and a pool all move the number too.

Location still varies inside a single neighborhood. Corner lots, backing to a busy road, backing to a park, or a water view all create real spreads. If your home backs to a highway and your comp has a wooded yard, note that the comp likely sold for more than yours would, which supports a lower value for your property.

You don't have to calculate every adjustment for a DIY appeal. A table of five comps with a column noting where your home is better or worse than each one is often enough to make the board stop and think.

How many comps do you need and how do you pick the best ones?

Three is the floor most boards will find credible. Five is the sweet spot. Past six or seven you're adding noise, not signal, unless your market is so thin you need breadth to prove your point.

To pick the best ones, start with your full raw list and cut in a fixed order. First cut: keep only arm's-length sales. Drop foreclosures, REO sales, short sales, and anything the county database flags as a non-market transfer. Second cut: time. Keep the most recent sales you can find. Third cut: location. Favor comps in the same neighborhood code or subdivision. Fourth cut: physical match. Keep the homes closest to yours in size, age, and condition.

From whatever survives, pick the three to five most similar homes with the lowest sale prices. Yes, you're choosing comps that help your case. That's appropriate and expected. The assessor picked comps that backed their value. You're building the counter-argument. Just don't cherry-pick so hard that you rely on a distressed sale or an obvious outlier, because the board will catch it and stop trusting everything else you brought.

One honest gut check. If your comps all cluster well below your assessed value, you have a strong case. If they scatter all over the place, the evidence is weaker, and you may need to reset your target value or reach for a different argument, like a property characteristic error on the record card.

How do you format a comparable sales report that a review board will actually read?

Keep it to one page if you can, two at most for the grid itself. A cover sheet with your parcel number, assessment date, your claimed value, and the basis for it (the comps) takes 30 seconds to read. That matters when a board is grinding through 40 appeals in a morning.

The grid itself is a simple table. Rows are properties, with your home in the first row. Columns are address, sale date, sale price, GLA (sq ft), price per square foot, year built, and a free-text column for key adjustments. Add an exterior photo of each comp if you can grab one from the listing or Google Street View. Boards are human, and photos make the comps feel real.

Under the grid, write two or three sentences: "The five sales above are arm's-length transactions occurring between [date] and [date] within [distance] of my property. They range from $[X] to $[Y], implying a value of approximately $[Z] for my home. My current assessed value of $[A] exceeds this market evidence by $[B]."

That's the whole thing. Don't write a brief. Don't apologize. Don't staple on ten pages of MLS printouts unless the board's rules demand backup.

If you want a pre-formatted template and instructions for turning the grid into an actual appeal filing, the TaxFightBack DIY appeal kit packages the form with step-by-step directions and keeps 100 percent of any savings in your pocket.

What adjustments should you make when comps aren't a perfect match?

Adjustments scare most homeowners, but you don't need an appraiser's precision. You need directional credibility, meaning you can say which way each difference pushes the price.

The cleanest DIY method is to note whether each comp is better or worse than your home on each key trait, then say whether that means the comp likely sold for more or less than your home would. For example: "This comp has a finished basement; my home does not. It likely sold for more than my home would, so the $310,000 sale price overstates my home's value, supporting my claimed value of $280,000."

Want numbers? Paired sales analysis is the cleanest route. Find two sales that are identical except for the one feature you're adjusting. The price gap between them is your adjustment. County mass appraisal departments often publish their own adjustment schedules. In Texas, county appraisal districts must make their appraisal manuals available to property owners. ^[5] Pulling the assessor's own adjustment grid and using their numbers is a strong move, because they can't argue against their own figures.

For most single-family appeals, square footage is the only adjustment that changes the conclusion in a real way. If your home is 1,800 square feet and your best comp is 2,000, even a conservative $50 per square foot cut means the comp's sale price should drop by $10,000 to compare apples to apples. Show that math in the table.

Can the assessor use different comps to counter your evidence?

Yes, and you should count on it. The assessor's appraiser may walk into the hearing with their own comp set, and those comps will, no surprise, support the assessed value. That's the adversarial shape of the process.

Your job is to guess which sales they'll reach for. Run a broader search before your hearing and hunt for recent sales near your home that exceed your assessed value. If any exist, work out why they don't apply to your property: different condition, larger lot, a recent renovation, a better location. Have the answer loaded before you sit down.

In most states the burden of proof at the first appeal level sits on you, the taxpayer, to show the assessment is wrong. ^[6] Some states shift that burden to the assessor at the appeals board level; others keep it on the taxpayer the whole way. Knowing your state's rule matters. In Illinois, the Cook County Board of Review runs a process where the taxpayer presents evidence first and the assessor responds. ^[7] In many states a presumption of correctness attaches to the assessment until you overcome it with substantial evidence.

The surest way to neutralize the assessor's comps is to attack their arm's-length validity. If their comp was a bank-owned property, a divorce sale, or a deal between related parties, say so with documentation. County recorder records often include affidavits of value or transfer disclosures that flag non-market sales.

What mistakes do most homeowners make when building a comp report?

Using distressed sales. A foreclosure or short sale that closed 30 percent below market makes your appeal look like you're gaming the system. The board will toss it and discount everything else you filed.

Ignoring the assessment date. Your county valued your home as of a specific date, often January 1 of the tax year. The relevant sales cluster around that date, not today's market. File six months into the year and pull comps from last month, and a falling market may help you, but a rising market means those newer comps could top your assessed value. Anchor your search to the lien date or assessment date on your notice, every time.

Submitting too many comps of uneven quality. Five strong comps beat fifteen mediocre ones. Boards give less credit to a pile of shaky evidence than to a short, clean, curated set.

Forgetting your own property's data. The grid needs your home in the first row. The board has to see what it's comparing against.

Using comps from a different market segment. Comps for your 1,100-square-foot townhouse should not include a 2,800-square-foot detached house two blocks away. Different product, different buyers, different math.

How does a comparable sales report differ from a full appraisal, and do you need one?

A full appraisal is a formal opinion of value from a licensed or certified appraiser. It includes an interior inspection, a reconciliation of multiple valuation approaches, a USPAP-compliant certification, and it typically costs $300 to $600 for a single-family home, more in high-cost markets. ^[8] A comparable sales report is a piece of that work, not the certified opinion.

Think of the comp report as the evidence document. In most residential tax appeals, a comp report you build yourself is enough at the informal and board-of-review levels. You don't need a full appraisal unless the stakes justify it or the state tribunal requires a certified opinion for a formal hearing.

Nobody has clean data on the win-rate gap between DIY comp reports and certified appraisals at board-of-review hearings. The closest published work is the Lincoln Institute of Land Policy's research on assessment appeals, which found that taxpayers with professional representation or formal appraisals tended to win larger reductions, while the presence of any credible evidence improved outcomes sharply compared to showing up with nothing. ^[9]

Here's the practical threshold. If the tax savings you're chasing tops about $1,000 per year, the math on a $400 appraisal starts to make sense. Below that, a solid DIY comp report is the right call. For large commercial properties or high-value residential estates, a certified appraisal is almost always worth it, because both the dollars at stake and the procedural complexity climb fast.

Do comparable sales rules differ by state?

They do, sometimes a lot. The core idea is universal, but the procedural details vary: which data sources count, how adjustments are treated, and what triggers a presumption of correctness.

In California, Proposition 13 caps assessed values at the 1975 base year plus 2 percent a year, so sales comparison evidence helps most either when you first buy (which resets the base) or when you argue current market value dropped below your base year value under Proposition 8. The relevant statute is Revenue and Taxation Code Section 51, which authorizes temporary reductions when current market value falls below the enrolled value. ^[10]

In Texas, county appraisal districts must appraise property at 100 percent of market value as of January 1 each year. Texas Tax Code Section 41.43 puts the burden on the appraisal district to prove value when its records don't support it. ^[5] Texas also runs informal hearings before the Appraisal Review Board, where a clean comp grid at the informal stage often settles the appeal without a formal hearing.

In Illinois, Cook County's process runs through the Cook County Assessor first, then the Board of Review. The Cook County Assessor publishes appeal guides noting that sales comparisons are the primary evidence type it accepts. ^[7]

In Georgia, counties like Gwinnett and Bexar County, Texas follow similar sales comparison frameworks with different deadlines and forms. Check the specific appeal procedures for your county before you submit. In Arizona, the Maricopa County assessor website publishes detailed guidance on comparable sales evidence requirements.

What should your final comparable sales report package include?

Here's the practical checklist. Assemble these before your hearing or before you mail the appeal.

A one-page cover sheet with your name, parcel number, property address, current assessed value, and your claimed value.

Your comp grid: a table with five to seven rows covering your property and four to six comps. Columns for address, sale date, recorded sale price, source (county recorder or MLS), GLA, year built, and an adjustment or notes column.

Photocopies or printouts of the county recorder entries for each comp confirming the sale price. This authenticates that the prices are real.

A street map or screenshot showing your property and each comp location, with distances labeled. One page.

A short explanation paragraph, two to four sentences, stating what the comps show and what value you're requesting. Not a legal brief.

If your property has condition issues, add a deferred maintenance page with three to five photos. Condition is a legitimate adjustment, and photos make it concrete.

Filing deadline documentation: a completed copy of your appeal form, the mailing address or submission portal, and the deadline date pulled straight from your county assessor or board of equalization website. Missing the deadline is the one mistake no amount of good evidence can fix. Illinois counties often run a strict 30-day window from the date of the assessment notice. ^[7] California's base deadline runs through November 30 of the assessment year for most counties, though the county clerk of the board sets the exact window. ^[10] Confirm yours before anything else moves.

Frequently asked questions

Can I use Zillow or Redfin sold listings as comps in my appeal?

Yes, with a caveat. Zillow and Redfin data come from MLS feeds that occasionally carry errors. Always cross-reference each sale price against your county recorder's deed records before you rely on a portal figure. Boards in most jurisdictions accept MLS data as supporting evidence; some formally require the county deed record as the authenticated source. Bring both to be safe.

What if there aren't enough recent sales near my home to build a comp report?

Expand two ways: stretch the time window to 24 months and widen the radius. Document why. Something like 'Only two arm's-length sales occurred within one mile in the past 12 months, so I expanded to a 3-mile radius and 24-month window.' For rural properties, some state statutes explicitly permit broader geographic and time searches. Check your state's assessment code or the assessor's appraisal manual.

Do I have to use comps that sold for less than my assessed value?

You should select comps that support your position, yes. Choosing favorable comps is standard practice for taxpayers and assessors alike; it's not dishonest. The rule is that your comps must be arm's-length sales of genuinely comparable homes. Don't use distressed sales or outliers just because they're low. A board that spots a cherry-picked foreclosure will discount your entire presentation.

How do I find out what the assessor's lien date or assessment date is for my county?

It's usually on your assessment notice or the county assessor's website. Most states set a statutory date: California is January 1, Texas is January 1, Illinois varies by county but is often January 1. Your state's department of revenue or property tax division publishes the calendar. Confirm the exact date, because your comps need to bracket that date, not today's.

Is a comparable sales report the same thing as a broker price opinion?

No. A broker price opinion (BPO) is an informal value estimate prepared by a licensed broker or agent, usually one to two pages. A comparable sales report is the evidence document that supports any value opinion, including a BPO or a formal appraisal. For a tax appeal you can submit a BPO as supporting evidence in many jurisdictions, but the underlying comp grid is what the board scrutinizes.

How does a tax assessor decide which sales are 'arm's length' when building their own comps?

Most assessors run a sales ratio study process that screens out non-arm's-length transactions. Common exclusions: sales between family members, nominal prices (under $1,000), REO or foreclosure, relocation company sales, and sales the grantor or grantee flagged as non-market. Many counties publish their exclusion criteria in annual ratio study documentation. Ask your assessor's office for the most recent ratio study to see what they excluded.

What is a sales ratio study and how does it relate to my appeal?

A sales ratio study compares assessed values to actual sale prices across a set of properties to measure assessment accuracy. The International Association of Assessing Officers (IAAO) sets the standard: median ratios should fall between 0.90 and 1.10, meaning assessments should land within 10 percent of market value. If your county's published ratio study shows a median above 1.0, assessments tend to run high, and that data supports your argument that yours is inflated too.

Can I appeal using only price-per-square-foot data without a full comp grid?

Some boards accept a straightforward price-per-square-foot argument when the neighborhood data is clear. You show that recent sales average $X per square foot, your home is Y square feet, so market value is roughly $X times Y, which is less than your assessed value. It works as a quick argument but runs weaker than a full grid because it hides the individual sales and skips property differences. Use it as a summary, not a substitute.

How do I handle a comp that sold higher than my assessed value?

Either exclude it (you're curating your strongest evidence) or include it and explain why it isn't comparable. A common reason: the comp had a finished basement, a recent kitchen renovation, or a much larger lot. Address it honestly in your notes column and the board sees you weighed the full picture. Ignoring an obvious high sale the assessor's appraiser will certainly cite looks worse than meeting it head on.

Does my appeal have a better chance if I hire an appraiser instead of using my own comp report?

A certified appraisal carries more formal weight, especially at state tax tribunal hearings where rules of evidence apply more strictly. At the informal and board-of-review levels, a well-prepared DIY comp report often lands similar percentage reductions at zero cost. The Lincoln Institute of Land Policy's appeals research suggests credible evidence matters more than who prepared it at the administrative stage. Spend the appraisal fee only when potential annual savings top roughly $1,000.

Can I look at comparable sales reports for commercial property appeals?

Commercial appeals lean on income capitalization more than sales comparison in most markets, because buyers of income-producing property price off net operating income rather than a per-square-foot basis. Sales comparison still applies to smaller commercial properties like strip retail or small office buildings, but the adjustments get more complex. For high-value commercial appeals, a certified appraisal with an income approach analysis is almost always necessary.

What if the assessor refuses to give me the sales data they used?

Most states require assessors to make their data available. Texas Tax Code Section 41.461 requires the appraisal district to provide the data, schedules, and formulas it relied on at least 14 days before a formal ARB hearing. In many other states, the public records law covers assessment records and the underlying sales data. File a formal public records request if the assessor's website has no searchable sales data. Keep a copy of the request and the response.

Sources

1. Appraisal Foundation, USPAP 2024 Edition (Definitions section): USPAP definition of arm's-length sale as a transaction between a willing buyer and seller each acting in their own best interest with adequate market exposure
2. International Association of Assessing Officers (IAAO), Standard on Mass Appraisal of Real Property: Preferred time and distance parameters for comparable sales selection in mass appraisal; rural properties may require broader geographic searches
3. Illinois Department of Revenue, Property Tax Assessment Practices Guide: County assessors assign neighborhood codes to parcels; comps within the same neighborhood code carry more weight than cross-neighborhood comparisons
4. Federal Housing Finance Agency, FHFA House Price Index datasets: FHFA House Price Index provides metro-level and state-level market trend data going back to 1991, useful for establishing market movement between valuation dates
5. Texas Comptroller of Public Accounts, Texas Property Tax Code Section 41.43: Texas Tax Code Section 41.43 shifts burden to appraisal district if records don't support the value; appraisal districts required to make appraisal manuals available to property owners
6. International Association of Assessing Officers (IAAO), Property Assessment Appeals Guide: At the initial appeal level in most states the burden of proof rests on the taxpayer to show the assessment is incorrect; presumption of correctness attaches to the assessment
7. Cook County Board of Review, Appeal Instructions and Evidence Requirements: Cook County Board of Review follows a process where the taxpayer presents evidence first; sales comparisons are the primary evidence type accepted for residential appeals; strict appeal windows apply from notice date
8. Appraisal Institute, Residential Appraisal Fee Survey (2023): A full certified appraisal for a single-family home typically costs $300 to $600, and more in high-cost markets
9. Lincoln Institute of Land Policy, Property Tax Assessment Appeals Research: Taxpayers with professional representation or formal appraisals tended to win larger reductions; presence of any credible evidence improved outcomes significantly compared to no evidence
10. California State Board of Equalization, California Revenue and Taxation Code Section 51: California R&TC Section 51 authorizes temporary reductions (Proposition 8) when current market value falls below the enrolled Proposition 13 base year value; appeal deadlines run through November 30 for most counties
11. IAAO, Standard on Ratio Studies (2013, reaffirmed 2023): IAAO standard requires median assessment ratios between 0.90 and 1.10, meaning assessments should be within 10 percent of market value for a jurisdiction to be considered uniformly assessed
12. Texas Comptroller of Public Accounts, Texas Property Tax Code Section 41.461: Texas Tax Code Section 41.461 requires appraisal districts to provide the data, schedules, and formulas used in valuation at least 14 days before a formal ARB hearing upon taxpayer request