How to build a comparative sales report for your property tax appeal

Last updated 2026-07-09

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

A comparative sales report is a table that lines up recent sales of homes like yours and shows what buyers actually paid. Assessors call it a sales comparison grid. Appraisers call it the sales comparison approach. The idea behind every name is the same. If comparable homes sold for less than the value your assessor put on your property, your assessment is too high and you are overpaying.

Property tax assessments in every U.S. state are supposed to reflect market value, meaning the price a willing buyer would pay a willing seller with no pressure on either side ^[1]. A comp grid is the most direct way to prove the assessor missed. It speaks the assessor's own language, because the assessor used sales data to set your value in the first place.

This matters more than most homeowners think. Anecdotes about your neighborhood and a stack of renovation receipts rarely move a hearing officer. A clean comp grid almost always does. The Lincoln Institute of Land Policy has documented that residential assessment errors are common and that market-based evidence is the strongest way to rebut them ^[2].

A comp grid is more than useful evidence. In most jurisdictions, it is the only evidence that routinely wins.

How is a comparative sales report different from a full appraisal?

A full appraisal from a licensed appraiser costs $300 to $600 for a typical single-family home and follows the Uniform Standards of Professional Appraisal Practice (USPAP). It includes a physical inspection, a written narrative, and a signed certification ^[3]. A comparative sales report you build yourself follows the same logic but needs no license, no inspection of the comps, and no USPAP compliance.

At an informal review or a county Board of Equalization hearing, a self-prepared comp grid is acceptable evidence in most states. Some states go further and put the burden on the assessor once you produce evidence of value. Texas Tax Code Section 41.43 says the appraisal district must prove the assessment is correct once the taxpayer offers evidence of market value ^[4]. Your comp grid is that evidence.

Here is when a full appraisal earns its cost. Pay for one if your potential savings are large (roughly $1,000 or more per year), if you are headed to a formal appraisal district review board or a state tax court, or if the assessor's attorney shows up. For most homeowners at the informal or board level, a well-built DIY grid does the same job for free.

One more difference. An appraisal ties its value to a specific date. Your grid has to tie to the assessment date (sometimes called the lien date or appraisal date) for your jurisdiction. Sales from the wrong time window get your evidence tossed on a technicality. That mistake is common, and it is avoidable.

What sales qualify as good comps for a property tax appeal?

Not every sale counts. You need arm's-length transactions, meaning the buyer and seller were independent, neither was under pressure, and the price reflects real market conditions ^[1]. Here is what to exclude:

• Foreclosure auctions and bank REO sales (distressed prices)
• Sales between family members or related entities
• Sales where one party was a government body
• New construction sold by a builder (different cost basis)
• Sales outside your jurisdiction's qualifying time window

The qualifying window varies by state. Most states look at sales in the 12 months before the assessment date. Some reach back further, and a few look forward. California's base-year system works differently from all of them, so check local rules first if you are appealing in Los Angeles or San Diego. Here is a quick reference for several large jurisdictions:

Jurisdiction	Assessment date	Typical comp window	Notes
Texas (statewide)	Jan 1	Prior 12 months	Arm's length required per Tax Code §23.01
Illinois (Cook County)	Jan 1	Prior 18-24 months	Three-year reassessment cycle [5]
California (most counties)	Jan 1 lien date	Prior 12 months	Prop 13 caps growth; comps matter at purchase or appeal
Georgia (statewide)	Jan 1	Prior 18 months	Fair market value standard per OCGA §48-5-2 [11]
Arizona (Maricopa)	Jan 1	Prior 24 months	Two-year look-back allowed for limited comparable sales
Florida (statewide)	Jan 1	Prior 12 months	Just value standard per Art. VII Sec. 4, FL Constitution [12]

Comps should be geographically close. In a dense suburb, aim for within one mile if you can. In a rural area, the same school district or township may be the best you get. Closer is always better, and a hearing officer notices when you reach into a different neighborhood to prop up your case.

Be honest with yourself. If the comps genuinely support a lower value, you have a real case. If you have to stretch geography or time to find them, you may not.

How do you find comparable sales data without paying for MLS access?

You do not need a Realtor login to find good comps. Several free sources give you most of what you need.

County deed records and assessor portals are the best place to start. Most county assessors publish sales data online, and most county recorders publish deeds with sale prices. Check your county assessor's website first. Maricopa property tax records and Los Angeles County property tax records are both searchable online and show recent sale prices.

Zillow, Redfin, and Realtor.com show recent sold prices for homes that went through the MLS. They lag sometimes and miss off-market sales, but they are free and usually accurate enough for a grid. Redfin lets you filter by sold date, square footage range, bedroom count, and lot size, which speeds up comp selection a lot.

The FHFA House Price Index will not give you individual comps, but it tells you how much values in your metro moved year over year. That helps if you are arguing the assessor used stale data ^[6].

State and county open data portals sometimes publish every recorded sale as a downloadable file. Search your county name plus 'real estate sales data' or 'deed transfer data.' A few states make this mandatory. New York publishes arm's-length sales by municipality through its Real Property System.

Here is what you cannot get for free: full MLS history, including days on market, listing price changes, and seller concessions. If the assessor argues your comps had concessions that pumped up the apparent price, you may not be able to rebut that without MLS data. A cooperating agent can run comps for you in exchange for a future listing, or you can buy a flat-fee comp report for $50 to $100.

How do you select the right comparable properties?

Start with your own home's physical facts: living area square footage, lot size, year built, bedrooms and bathrooms, garage, pool, and condition. Your search filters should mirror these as closely as you can manage.

Square footage is the variable that matters most. Most appraisers try to stay within 10 to 20 percent of the subject's size. An 1,800 square foot house compared against a 2,500 square foot house is a weak comp unless you make a large, defensible adjustment.

Year built matters more than people expect. A 1960s ranch and a 1990s colonial can be the same size on the same street and still draw different buyers, because they carry different construction quality and different systems. Try to stay within 15 to 20 years of your home's age.

Condition is where DIY analysis gets tricky. You cannot walk through the comps. You can study listing photos if the sale was MLS-listed, and you can pull the assessor's property record card for each comp to see its condition grade. If a comp sold high because it was just renovated and yours was not, that comp hurts you unless you adjust it down.

Aim for 3 to 6 comps. Three is the floor most hearing officers want. Six looks thorough. More than six usually adds noise unless the sales are genuinely tight.

How do you make adjustments to comparable sales?

Adjustments are dollar or percentage additions and subtractions that account for the differences between each comp and your home. If a comp has a pool and yours does not, you subtract the estimated pool value from the comp's sale price. If a comp is 200 square feet smaller, you add the value of that space to the comp's sale price.

The direction has to be right. Ask yourself one question for each feature: if the comp matched my home, would it have sold for more or less? If more, add to the comp. If less, subtract from the comp. The result is the adjusted sale price, your estimate of what the comp would have fetched if it were your home.

Where do the dollar amounts come from? For a DIY grid, use paired sales analysis when you can find it. A paired sale is two homes that sold close in time and are identical except for one feature. If home A with a garage sold for $20,000 more than home B without one, you have a market-derived garage adjustment. Assessors use this exact method.

When paired sales are not available, published cost data holds up. The Marshall Valuation Service and the National Association of Home Builders publish cost figures for garages, pools, finished basements, and extra bathrooms. You probably will not have full Marshall Valuation access, but NAHB and some state extension services publish periodic cost guides you can cite in a hearing ^[7].

Keep adjustments conservative. Adjust every comp down hard and the hearing officer assumes you are cherry-picking. A useful self-check: if the net adjustment on a single comp exceeds 25 percent of the sale price, that comp is probably not comparable enough to use. Appraisers call this the 15/25 guideline (no single adjustment over 15 percent, net adjustments under 25 percent). It is not a legal standard, but it keeps you honest ^[3].

After adjusting, bracket the values. Bracketing means your comps straddle your argued value, some above and some below. If every adjusted comp lands right at your target, it looks engineered. If they bracket it naturally, it looks like the truth.

What does a comparative sales report actually look like on the page?

You do not need special software. A spreadsheet or a printed table works fine. Here is the structure hearing officers expect:

Field	Your property	Comp 1	Comp 2	Comp 3
Address	123 Main St	456 Oak Ave	789 Elm Dr	321 Pine Rd
Sale date	n/a (subject)	03/15/2024	07/22/2024	11/01/2023
Sale price	n/a	$310,000	$298,000	$325,000
Sq ft living	1,850	1,780	1,920	1,900
Sq ft adj	n/a	+$4,900	-$4,900	-$3,700
Garage	2-car	2-car	1-car	2-car
Garage adj	n/a	$0	+$8,000	$0
Pool	No	No	No	Yes
Pool adj	n/a	$0	$0	-$12,000
Year built	1988	1991	1986	1990
Year built adj	n/a	-$1,500	$0	-$1,000
Total net adj	n/a	+$3,400	+$3,100	-$16,700
Adjusted sale price	n/a	$313,400	$301,100	$308,300

From those three adjusted prices you would conclude a market value near $307,600 (the average), or you present the range ($301,100 to $313,400) and argue that your assessment of, say, $340,000 sits above the top of the market. That is a clean argument.

Attach a one-paragraph narrative that explains your method: what you searched for, what you excluded and why, and what the adjusted values point to. Keep it to half a page. Hearing officers review dozens of appeals a day. Brief and clear wins.

What if the assessor has their own comps that show a higher value?

This happens. The assessor may bring their own sales comparison to the hearing, or the burden-of-proof rules may require you to knock down their evidence rather than just present yours.

Read their comps carefully first. Assessors sometimes use sales from outside the neighborhood, lean on non-arm's-length transfers, or skip adjustments for real differences. Each of those is a fair rebuttal. If they used a foreclosure or a related-party transfer, say so directly and name the sale.

If their comps are genuinely better, that tells you something too. Maybe your assessment is fair and your energy belongs elsewhere. Honest self-assessment before the hearing saves you a wasted afternoon.

Texas Tax Code Section 41.43 puts the burden on the appraisal district once you show evidence of value ^[4]. Illinois shifts the burden under 35 ILCS 200/16-185 once the taxpayer makes a prima facie case ^[10]. Know your state's rule, because it changes how you frame the presentation. If the burden sits with the assessor from the start, your grid only needs to raise a genuine dispute. If it starts with you, your grid has to affirmatively prove the lower value.

For high-stakes disputes, have a property tax consultant or a licensed appraiser review the assessor's grid before the hearing. A single one-hour consult ($100 to $200) can surface flaws you would miss on your own.

How do time adjustments work when the market moved fast?

If home values in your area rose or fell a lot between your comp sale dates and the assessment date, you may need a time adjustment (also called a market conditions adjustment). Skipping it in a rising market actually helps you, because unadjusted older comps show lower values than the assessment date. In a falling market, you may need to adjust older comps downward to the assessment date.

The FHFA House Price Index is a free, citable source for quarterly price changes by metro area ^[6]. If the index shows values in your metro fell 4 percent between a comp's sale date and your assessment date, apply a negative 4 percent time adjustment to that comp's price.

Be careful. Time adjustments need defensible data and a plain explanation. Apply one you cannot explain at the hearing, and the assessor will pull the thread until it unravels. Only use a time adjustment when a published index or a local brokerage market report backs it up.

Does a comparative sales report work differently for condos, townhomes, or land?

The logic holds. The adjustment categories change.

For condos, floor level, view, and HOA fees turn into material adjustments. Two units in the same building on different floors with different views can carry very different values, and the assessor may not have caught it. Recent sales in the same building or complex are your strongest comps.

For townhomes, end unit versus interior unit is a real distinction in most markets, often worth $10,000 to $25,000 depending on size. Parking (attached versus detached) and HOA fees matter too.

For vacant land, comps have to account for size, frontage, topography, zoning, utilities, and access. The unit of comparison is price per square foot of land or price per acre, not price per square foot of living area. Land comps are harder to find and the adjustments get specialized. If your land value is large, a licensed appraiser is probably worth the cost.

For commercial property, the sales comparison approach is one of three methods (income and cost are the others), and the income approach often dominates. Commercial grids get complex fast. For anything above a few units, a DIY effort is usually the wrong tool.

How do you present your comparative sales report at the hearing?

Bring four copies: one for you, one for the hearing officer, one for the assessor's representative, and a spare. Some boards set submission deadlines days before the hearing, not the day of, so check your county's rules.

Many counties now take electronic submissions. If yours does, send a PDF with bookmarked sections: your comp grid, the property record cards for each comp (printed from the assessor's own website, which makes them hard to dispute), and the deed records showing sale prices.

Open with your conclusion. Say: 'The three comparable sales in my grid point to a market value near $307,600. The current assessment of $340,000 is about 10.5 percent above market.' Then walk through the grid. Hearing officers do not want an appraisal lecture. They want the math and the number you are asking for.

Expect one or two challenges. Why did you exclude a particular sale? Why did you make a specific adjustment? Practice short, factual answers. 'I excluded 411 Maple Street because it transferred between a parent and subsidiary entity, which disqualifies it as arm's-length under [your state's] assessment law.' Specific and calm beats passionate and vague every time.

If you want a running start on all of this, the TaxFightBack appeal kit walks through the grid format step by step with state-specific deadlines.

For county procedural rules, read the assessor's own guidance. Cook County tax assessor tax bill and Bexar County tax assessor both publish detailed appeal instructions, including which evidence they accept.

What common mistakes cause comp grids to fail at hearings?

Using distressed sales as comps. A foreclosure or short sale used to argue your home is worth less is the most common and most easily dismissed mistake. The assessor's rep flags it on sight.

Using too few comps. One or two sales look cherry-picked even when they are perfectly valid. Three is the floor. Five is comfortable.

No adjustments at all. Present raw sale prices and you are implying the comps are identical to your home. If they are not, the hearing officer makes mental adjustments, and those may not go your way.

Over-adjusting. When net adjustments on a comp pass 20 to 25 percent, that comp arguably is not comparable. Drop it and find a better one.

Ignoring your home's advantages. If your home has a finished basement and none of the comps do, adjust the comps upward. Do not leave it blank. Hiding your own advantages torches your credibility more than it helps.

Wrong assessment date. Your comps have to reflect value as of the assessment date, not the hearing date. If values shifted between those dates, acknowledge it and address it.

Skipping the assessor's own property cards. When you pull comp data from the assessor's website and bring printouts, the assessor cannot argue with the underlying numbers. They are the assessor's numbers. That one step removes a whole line of attack.

Local quirks matter. Gwinnett County tax assessor, Cherokee County tax assessor, and Coweta County tax assessor in Georgia each run slightly different board procedures and submission windows that shape how you present your evidence.

When should you hire a professional instead of building the comp grid yourself?

Do it yourself when your property is residential, your potential annual savings are under $1,000, you are headed to an informal review or a first-level board hearing, and comparable sales are easy to find in your area.

Hire a licensed appraiser when your potential savings top $1,500 a year, when you are going to a formal hearing or state tax court, when your property is unusual (waterfront, historic, acreage), or when the assessor brings professional representation.

Hire a property tax consultant (licensed appraiser or not) when the contingency fee is low and you honestly lack the time. Know what you are trading away. Contingency firms typically take 30 to 50 percent of one year's savings ^[8]. On a $2,000 annual reduction, that is $600 to $1,000 out of your pocket for work you could finish in a few hours.

There is a middle path. Pay a flat-fee consultant to review your self-prepared grid before the hearing. Many pros offer this for $75 to $150. You keep the savings and you get a trained eye on your evidence.

For state-specific professional standards, the Madison County tax assessor and Lake County property tax pages both link to their state's assessment standards documentation.

Frequently asked questions

How many comparable sales do I need in my report?

Most hearing officers want at least three. Five or six is a stronger showing. If your neighborhood has few sales, two comps with very tight similarity to your home can work, but explain in your narrative why more were not available. Fewer than three invites the assessor to argue you cherry-picked the most favorable sales.

Can I use Zillow or Redfin sold prices in my comp grid?

Yes, as long as you confirm the price against the county deed record. Print the deed (free from your county recorder's website) and attach it to your grid. Zillow and Redfin work as finding tools, but the deed is the primary document because it is the official public record of the transaction price.

What is the difference between assessed value and market value?

Market value is what a buyer would pay in an open sale. Assessed value is what the assessor assigned for tax purposes. In many states these are meant to be equal, but some assess at a fraction of market value (for example, 25 percent in Tennessee or 10 percent for residential property in Illinois). Target the market value standard your state uses, not the fractional assessed value.

Do I need to adjust for the date of the comp sales?

Only if the market moved materially between the comp sale date and your assessment date. In a stable market, no adjustment is needed. In a market that rose or fell more than 3 to 5 percent, a time adjustment is defensible if you back it with a published index like the FHFA House Price Index. Without data, skip it rather than risk a challenge.

What if there are no comparable sales near my property?

Broaden your search step by step: same subdivision, then same school district, then same municipality. Acknowledge the distance in your narrative and explain why you had to look farther. You can also supplement with a cost approach (replacement cost minus depreciation) if sales are genuinely thin, but the cost approach is harder to present without professional help.

Can I use a comparative sales report to appeal in any state?

Yes. Every U.S. state accepts the sales comparison approach as at least one method of establishing market value for residential property. The submission procedures vary by state and county, but the legal standard is market value, and a comp grid speaks directly to that standard. Check your state's assessment law for the exact definition of value used.

What happens if the assessor's comps are better than mine?

You have options. Challenge their comps on arm's-length grounds, geographic distance, or missing adjustments. Supplement with additional comps that were in neither analysis. Or honestly reconsider whether your assessment is correct. Withdrawing a weak appeal before the hearing protects your credibility and saves the time cost of a losing argument.

How do I find the property record cards for comparable homes?

Most county assessors publish property record cards online. Search your county assessor's website for the comp's address. The card shows square footage, bedroom and bathroom count, year built, condition grade, and the features the assessor used to value the property. Print one for every comp. They let you make precise adjustments, and they come from the assessor's own data, which makes them hard to dispute.

Is a comparative sales report the same as a broker price opinion (BPO)?

Not exactly. A broker price opinion is prepared by a real estate broker and has a specific legal definition under many state licensing laws. A comparative sales report for a tax appeal follows the same method as a BPO but is not a licensed document. In most jurisdictions a BPO is acceptable evidence at an informal tax review. Check your county's evidence rules.

Do appeal success rates differ by how many comps I use?

Nobody has good public data on comp count versus success rate specifically. The closest evidence comes from IAAO (International Association of Assessing Officers) standards, which call for a minimum of three sales in a grid and prefer five or more for a credible conclusion. Meeting that standard gives your evidence the same weight the assessor's evidence carries ^[9].

What if my home sold recently for less than my assessment?

That is your single strongest comp. A recent arm's-length sale of the subject property is the best possible evidence of market value in most jurisdictions. Attach the settlement statement or deed, confirm the sale was arm's-length, and note the sale date against your assessment date. Many assessors adjust the value at the informal review stage, no hearing needed, once they see a recent sale price.

How long does it take to build a comp grid for a typical home?

Plan on 2 to 4 hours the first time, including finding sales data, pulling property cards, making adjustments, and writing the narrative. Once you have done it once, later years take about an hour. That time pays for itself before you hand a contingency firm 30 to 50 percent of your savings.

Sources

1. International Association of Assessing Officers (IAAO), Standard on Mass Appraisal of Real Property: Property tax assessments are supposed to reflect market value, defined as the price a willing buyer would pay a willing seller with no pressure on either side.
2. Lincoln Institute of Land Policy, research on inequality in property tax assessments: Residential assessment errors are common and presenting market-based evidence is the most effective rebuttal strategy.
3. The Appraisal Foundation, Uniform Standards of Professional Appraisal Practice (USPAP): A full licensed appraisal requires a physical inspection, detailed narrative, and signed certification under USPAP; the 15/25 guideline for adjustments is a widely recognized appraisal practice standard.
4. Texas Statutes, Texas Tax Code Section 41.43: Texas Tax Code Section 41.43 places the burden on the appraisal district to prove the assessment is correct once the taxpayer produces evidence of market value.
5. Cook County Assessor's Office, assessment process overview: Cook County operates on a three-year reassessment cycle with a typical comp window of 18 to 24 months prior to the assessment date.
6. Federal Housing Finance Agency, House Price Index (FHFA HPI): The FHFA House Price Index provides quarterly price changes by metropolitan area and can be used to support time adjustments in a comp grid.
7. National Association of Home Builders, housing cost data: NAHB publishes periodic cost data for housing features such as garages, pools, and finished basements usable as adjustment support in tax appeal evidence.
8. National Taxpayers Union Foundation, property tax relief guidance: Contingency-fee property tax firms typically charge 30 to 50 percent of one year's tax savings.
9. International Association of Assessing Officers, valuation standards: IAAO standards call for a minimum of three sales in a comparable sales grid and prefer five or more for a credible value conclusion.
10. Illinois General Assembly, 35 ILCS 200/16-185, Property Tax Code: Illinois law shifts the burden of proof to the assessor once the taxpayer produces a prima facie case of over-assessment.
11. Georgia General Assembly, Official Code of Georgia Annotated Section 48-5-2: Georgia uses a fair market value standard for property tax assessments and a typical comp window of the prior 18 months.
12. Florida Department of Revenue, Property Tax Oversight, just value standard: Florida uses a just value standard under Article VII Section 4 of the Florida Constitution with a 12-month comp window.