How to prepare a comparable sales grid for an assessment appeal

Last updated 2026-07-11

What is a comparable sales grid and why does it matter for appeals?

A comparable sales grid, sometimes called a sales comparison grid or adjustment grid, is a table that turns recent home sales into an opinion of what your property is worth on the open market. Each row is one comparable sale. Each column is a feature: square footage, bedroom count, garage size, lot area. You enter the actual number for each comp and for your own house, then calculate dollar adjustments for every difference.

Here is why it carries so much weight. Most state statutes require assessors to value property at market value, defined by what a willing buyer would pay a willing seller in an arm's-length deal ^[1]. A grid built on real sales is the most direct proof your assessment misses that mark. Testimony, photos, even a formal appraisal all have to connect back to sales data at some point. The grid is that connection.

Appeal boards see grids all day. Residential appeals in Illinois, for one, are decided almost entirely on comparable sales evidence presented in grid form ^[2]. A legible grid with honest adjustments beats a stack of printouts or a vague claim that other houses sold for less.

You do not need to be a licensed appraiser to submit one. Many jurisdictions let homeowners present their own comparable sales evidence. What the board wants is numbers that trace back to documented, verifiable sales, not figures you guessed at.

How do I find comparable sales that appeal boards will actually accept?

Start with your county assessor's website or a public property records portal. Most counties keep a searchable database of recorded deeds and sale prices, usually tied to parcel maps. Your state may run a statewide sales file too. Illinois publishes its PTAX-203 transfer declaration data, and New York's Office of Real Property Tax Services publishes annual sales reports ^[3].

Three filters decide whether a sale belongs in your grid: recency, location, and physical similarity.

Recency. Most boards want sales that closed within 12 months of the assessment date. Some stretch to 24 months when the market is thin, but closer to the lien date is always better. Cook County's Board of Review generally requires sales within the 12-month period ending on the assessment date ^[2].

Location. Pull comps from the same neighborhood or subdivision when you can. If you can't, use the same school district or the same assessor-defined neighborhood code. Crossing a major boundary weakens your grid: a highway, a school district line, a flood zone edge.

Physical similarity. Aim for sales where the gross living area (GLA) sits within roughly 15 to 20 percent of your home's GLA. An 1,800-square-foot house pairs well with comps from about 1,500 to 2,150 square feet. Keep bedroom and bathroom counts close. Keep age within a decade or two unless the whole neighborhood is one vintage.

Now scrub the list. Cut foreclosure deeds, sheriff's sales, quitclaim transfers between relatives, and estate sales where the recorded price may not reflect the market. The International Association of Assessing Officers defines an arm's-length transaction as one where "both buyer and seller are typically motivated, well-informed, and neither is under undue pressure" ^[4]. Hold every sale up to that test.

Get at least three comps. Six is better. Three is the floor most boards take seriously.

What columns belong in a comparable sales grid?

Your grid has two halves: data fields and adjustment fields. Here is what a standard residential grid holds.

Data fields (the raw facts, no adjustments yet):

• Address
• Sale date
• Sale price
• Financing (conventional, cash, FHA, seller-financed)
• Condition at sale
• Above-grade GLA in square feet
• Bedroom count
• Full and half bath count
• Garage (attached, detached, none; number of cars)
• Basement (finished area in sq ft, unfinished area in sq ft)
• Lot size
• Year built
• Pool or other significant amenity

Adjustment fields sit next to each feature where your home differs from the comp. The rule runs one direction: where the comp is better than your house, subtract from its sale price; where the comp is worse, add. You're answering a single question. What would this comp have sold for if it were identical to my house?

The adjusted sale price is that comp's estimate of your home's market value. After you adjust all three to six comps, you reconcile them into one value, usually a weighted result or the midpoint of a tight cluster.

Formatting tip. A landscape spreadsheet reads best. Put the subject property in column B and each comp in columns C through H. Features run down the rows. Bold the adjustment rows so the board can scan them fast. Export to PDF before you file.

How do I calculate dollar adjustments for differences between properties?

This is where most DIY filers stall. Good news: you don't invent adjustment amounts out of thin air. Three reliable methods exist.

Paired sales analysis. Find two sales in your market that differ in exactly one feature. One house has a garage, an otherwise identical house doesn't. The price gap is your market-derived adjustment for a garage. This is what appraisers use and what IAAO recommends ^[4]. It takes time. It also holds up.

The assessor's own schedule. Your assessor may publish a depreciation or cost schedule that implies per-square-foot values for property components. Say the assessor values finished basement space at $25 per square foot and your comp has 400 more finished square feet than your home. A negative $10,000 adjustment is reasonable, and it comes straight from the assessor's own data. Turning the assessor's numbers against the assessment is a strong move.

Published market data. Real estate agents often publish adjustment ranges for a local market, and some state appraisal boards issue guidance. The Appraisal Foundation flags adjustments above 10 percent of sale price for any single line item, more than 25 percent net, or more than 35 percent gross as signs the comp is too dissimilar to trust ^[5].

Adjustment amounts swing wildly by market, so skip the national rules of thumb. A bathroom addition might add $8,000 in rural Georgia and $35,000 in San Francisco. Tie your adjustments to local evidence every time you can.

Honest caveat: nobody has clean data on adjustment amounts at the neighborhood level. When the board asks how you got a number, the answer should be "paired sales from the same market" or "the assessor's published schedule." Not "I found it online."

Show your math inline. A cell that reads "-$5,000" with no explanation draws skepticism. A cell that reads "-$5,000 (comp has 1-car garage vs. subject's 0-car garage; adjustment per paired sales analysis of [address] and [address])" is hard to wave away.

What does a completed grid actually look like? (sample layout)

Here is a simplified example. Real grids carry more rows, but this shows the logic.

Feature	Subject	Comp 1	Adj 1	Comp 2	Adj 2	Comp 3	Adj 3
Address	12 Oak St	88 Elm Ave		54 Maple Dr		7 Pine Ln
Sale date	n/a	3/15/2024		6/02/2024		9/18/2024
Sale price	--	$285,000		$295,000		$278,000
GLA (sq ft)	1,640	1,710	-$3,500	1,600	+$2,000	1,640	$0
Bedrooms	3	3	$0	3	$0	3	$0
Full baths	2	2	$0	2	$0	1	+$6,000
Garage	None	1-car	-$8,000	None	$0	None	$0
Basement fin.	0 sq ft	0 sq ft	$0	200 sq ft	-$4,000	0 sq ft	$0
Year built	1978	1979	$0	1975	+$1,500	1980	$0
Net adjustment			-$11,500		-$500		+$6,000
Adjusted price			$273,500		$294,500		$284,000

Indicated value of the subject: $273,500 to $294,500, midpoint around $284,000. If the assessed value is $310,000, the grid supports a reduction of roughly $26,000. At a 1.5 percent tax rate, that saves about $390 a year.

State a conservative reconciled value. Boards respond better to a modestly supported number than to the lowest adjusted sale. With adjusted prices of $273,500, $294,500, and $284,000, arguing for $274,000 looks aggressive. Arguing for $280,000 to $284,000 looks credible.

How do I reconcile multiple comps into one value conclusion?

Reconciliation is where you weigh your comps and land on the single number for your petition. It's more than averaging.

Give the most weight to comps that needed the fewest and smallest adjustments. A sale with a net adjustment of $500 on a $285,000 price is far more reliable than one with a net adjustment of $22,000. The IAAO's Standard on Ratio Studies frames the goal as selecting the sales that most closely mirror the subject property ^[4].

Say one comp sits in the same subdivision, closed two months ago, and needed only minor adjustments. Weight it heavily, maybe 60 percent of your conclusion. The other two split the remaining 40 percent.

Write two or three sentences of reconciliation under the grid. Something like: "Comp 3 is given primary weight because it matches the subject in bedroom and bath count, needs no garage adjustment, and closed within 90 days of the assessment date. Comps 1 and 2 corroborate the conclusion but required larger adjustments for garage and basement differences. The reconciled value is $282,000."

That short narrative tells the board you understand the analysis, more than that you ran a spreadsheet.

What are the most common mistakes that get comp grids rejected or ignored?

Using non-arm's-length sales is the fastest way to lose credibility. If the board pulls one of your comps and finds a foreclosure or a family transfer, the whole grid falls under suspicion. Pull the deed, check the transfer type, confirm the grantor and grantee are unrelated, then use the sale.

Using comps that are too different from your property is the second most common error. A 1,640-square-foot ranch does not compare to a 2,800-square-foot colonial, same street or not. The adjustments would blow past any reasonable threshold, and the board tosses the comp.

Undisclosed time adjustments are subtler. If prices in your market rose 6 percent between a comp's sale date and the assessment date, a comp from 18 months ago needs a downward time adjustment to reflect what it would fetch on the assessment date. Skip that adjustment when prices moved and your grid reads as inaccurate. Show it.

Gross adjustment problems come next. If a single comp needs gross adjustments over 35 percent of its sale price, most appraisal standards call it too dissimilar to use ^[5]. Drop it. Find a better one.

Sloppy presentation gets grids dismissed on looks alone. Illegible fonts, missing addresses, mismatched column labels: reviewers distrust the numbers underneath. Use a template. Print clean copies. Bring extras.

One more. Arguing for a value below your lowest adjusted comp backfires. If your three adjusted values are $276,000, $283,000, and $291,000, asking for $265,000 reads like gaming the process. Ask for a number your grid actually supports.

Do I need a licensed appraiser to prepare a comp grid, or can I do it myself?

In most jurisdictions, homeowners can present their own comparable sales evidence at an informal hearing or before a county board of review without a licensed appraiser. The rules vary by state.

The Illinois Property Tax Appeal Board accepts residential appeals from property owners with no requirement for professional representation ^[2]. The Cook County Board of Review likewise takes homeowner submissions that include sales evidence. Texas law gives owners the right to present evidence directly at the Appraisal Review Board hearing, comparable sales included ^[6].

Where you almost certainly need a licensed appraisal is at the state tax court level, if your informal and board appeals fail, or for commercial property in most states. A formal report prepared under USPAP (Uniform Standards of Professional Appraisal Practice) is required in many court proceedings.

At the administrative stages, a well-built DIY grid often beats a rushed professional one. The board judges the quality of the evidence, not the credential on the cover. A grid that's clean, sourced, and internally consistent stands on its own.

Want a template that walks through every column and adjustment line? TaxFightBack's appeal kit includes a pre-formatted comparable sales grid built for residential appeals at the board level.

One case where paying for an appraiser makes sense: when your projected tax savings over five years clear the appraisal fee (usually $400 to $700 for a residential appraisal) ^[7], or when you've already lost at the board level and plan to file in state tax court.

How does the assessor's own comparable sales analysis compare to mine?

Many assessors run mass appraisal systems, usually CAMA (computer-assisted mass appraisal) software, to value thousands of properties at once. These systems apply neighborhood-level regression models instead of property-by-property grids. The IAAO's Standard on Mass Appraisal of Real Property sets acceptable performance at a median assessment ratio between 0.90 and 1.10, with a coefficient of dispersion (COD) below 15 for residential properties in most markets ^[8].

Here's what that means for you. The assessor's model aims to be accurate on average, not accurate for any single house. Your property can be badly overvalued even when the county's overall ratio statistics look fine.

When you appeal, you can sometimes request the sales the assessor used to calibrate your neighborhood's model. If those sales skew toward higher-priced homes and leave out the modest ones, that's a real analytical flaw you can raise. Some assessors share their comparable sales on written request. Others require a formal records request under your state's open records law.

Comparing your grid against the assessor's model output is legitimate evidence. The assessor's system pegged your house at $310,000, but all six of your arm's-length comps adjust to a range of $275,000 to $290,000. That mismatch is the story you tell the board.

If you're in a county like Cook County or LA County, the assessor publishes neighborhood median ratios that help you argue your property is an outlier within the assessor's own statistics.

What evidence should I bring to the hearing alongside the grid?

The grid is your centerpiece. It works better surrounded by supporting documents.

Sale deeds or MLS data sheets for each comp. Print the public record showing the sale price, date, and parties. If you can get MLS data through a real estate agent, a listing printout with condition, features, and photos is better still. This lets the board see the sale was arm's-length and that the features you listed are accurate.

Photos of your property. Condition drives value. If your roof needs replacing, the furnace is original to 1978, or the basement took on water, photos document deferred maintenance that pushes your value down. Photos of superior comps help too, showing the board why those homes sold higher.

The assessor's property record card for your home. Request it before the hearing. These cards carry errors constantly: wrong square footage, wrong bedroom count, wrong year built. A documented error on the assessor's own record is powerful independent evidence.

Your notice of assessment. Bring the original showing your current assessed value and its effective date.

For markets like Montgomery County or Gwinnett County, local assessor offices publish appeal procedures that spell out which documents to bring. Read the local rules before you walk in.

Bring five copies of everything: one for you, one for each board member (most boards seat three), one for the assessor's representative. Organized evidence makes reviewers more receptive. Small logistics, real difference.

How do comparable sales grids work differently for condos and townhouses?

Condos and townhouses add wrinkles that single-family grids don't have.

For condos, GLA is measured interior wall to interior wall, and common areas don't count. The features shift: floor level, view, parking (deeded vs. undeeded, interior vs. surface), storage unit, HOA fees, building amenities. HOA fee gaps sometimes get adjusted directly. If your comp carries a $150-a-month higher fee, some appraisers capitalize that at a market rate and subtract it from the comp's price.

The main rule for condo comps: use sales from the same project or building first. Sales from a different building, even next door, drag in location and building-quality variables that are hard to isolate. If you have to go outside the project, note that no same-project sales closed in the relevant window and explain why.

Townhouses sit between condos and detached homes. If yours has its own lot, even a small one, treat GLA and lot size as adjustment items. If it's a fee-simple townhouse in a planned community, handle the HOA fees and common amenities the way you would for a condo.

In dense urban markets like New York City, the analysis for a co-op or condo unit turns technical fast. The NYC property tax system adds a layer because residential co-ops and condos are assessed with an income approach, not comparable sales directly. There, your strategy may look nothing like the grid approach that works elsewhere.

What deadlines apply to filing an appeal with a comp grid?

Deadlines are statutory and almost never waivable. Miss the filing date and you wait another full year, no matter how strong your grid is.

State law sets these dates, and they vary a lot. A few examples from publicly available state statutes:

State	Informal/Board appeal deadline	Governing statute
Illinois	30 days from assessment notice mailing	35 ILCS 200/16-55
Texas	May 15 or 30 days from notice, whichever is later	Tex. Tax Code § 41.44 [6]
California	September 15 (most counties) or November 30 in some	Cal. Rev. & Tax Code § 1603
New York	Varies by jurisdiction; often 3rd Tuesday in June	RPTL § 524 [3]
Georgia	45 days from assessment notice	O.C.G.A. § 48-5-311

The assessment date (the "lien date" or "valuation date") also governs which sales count for your grid. California's lien date is January 1 ^[9]. Texas uses January 1 too ^[6]. Your comps should bracket that date.

Some counties let you file a grid with your initial petition, then update or supplement it before the hearing. Others demand all evidence at filing. Check your local board's rules of procedure. The Bexar County appraisal review board, for example, requires you to exchange evidence with the appraisal district at least 14 days before the hearing ^[6].

Set a calendar reminder 60 days out. You need time to pull sales, build the grid, gather documents, and file.

Frequently asked questions

How many comparable sales do I need for a property tax appeal grid?

Three is the practical minimum most boards consider. Six is better because it shows the pattern isn't driven by one odd sale. If your neighborhood is small and recent sales are scarce, two can work, but you'll need to explain the thin market in writing. Appraisal standards and IAAO guidance consistently favor three to six comps for residential properties.

Can I use Zillow or Redfin sales data in my comp grid?

Use Zillow or Redfin to spot candidate comps, but verify each sale against the county recorder's deed records before you cite it. Public deed records are authoritative; Zillow's reported prices sometimes carry errors or reflect non-arm's-length transfers. The board wants a source it can check, and the county recorder's database is that source.

What if no comparable sales exist close enough to my property?

Expand your search radius gradually and document why you had to go further. Note the shortage of closer sales in your grid narrative. You can also use older sales with explicit time adjustments, or sales from an adjacent neighborhood with a brief note on why it's economically similar. Boards understand thin markets. What they won't accept is no explanation for why comps are dissimilar.

How do I adjust for age and condition differences between my home and a comp?

Age adjustments stay modest unless a renovation is involved. Condition adjustments run larger. Use the assessor's rating scale if they publish one: many CAMA systems rate condition (poor, fair, average, good, excellent) and imply a percentage premium per step. If your home is average and the comp sold in good condition, a downward adjustment of 5 to 10 percent of sale price is commonly supported in appraisal literature.

Should I include the assessor's own sales in my grid to use against them?

Yes, and it's one of the most effective tactics you have. If the assessor used sales to calibrate your neighborhood and those sales support a lower value than your assessment, putting their own data in your grid is internally consistent and hard for the board to brush off. Request the assessor's comparable sales data before the hearing through a public records request if it isn't already online.

What is a gross adjustment and why does it matter for comp selection?

Gross adjustment is the total of all individual adjustments regardless of sign: you add the positive and negative adjustments together without letting them cancel out. The Appraisal Foundation's guidelines suggest gross adjustments above 35 percent of a comp's sale price, or net adjustments above 25 percent, signal the comp is too dissimilar to trust. If your grid needs a 40 percent gross adjustment to make a comp work, find a different comp.

Do I need to adjust for market conditions (time adjustments) in my comp grid?

Yes, if prices moved materially between the comp's sale date and the assessment date. In a market where prices rose 8 percent over 12 months, a sale from 12 months before the assessment date needs a downward adjustment of roughly 8 percent to reflect what it would fetch on the valuation date. Support the rate with a local price index, the assessor's published market statistics, or paired sales across time.

What happens at the hearing if the assessor challenges one of my comps?

Stay calm and be ready to explain why you picked each comp and how you derived each adjustment. If the assessor shows a comp was a non-arm's-length sale, acknowledge it and explain that your remaining comps still support your conclusion. Six comps instead of three gives you room to lose one or two without losing the argument. Know your backup answer for every comp before you walk in.

Can I use foreclosure sales or REO sales as comps?

Generally no. Foreclosure sales, REO (real estate owned) sales, and bank sales count as non-arm's-length transactions because the seller is under duress and lacks full market motivation. IAAO standards explicitly exclude these from arm's-length sales databases used in ratio studies. Putting them in your grid will draw an immediate challenge from the assessor's representative.

How do I present a comp grid if the hearing is remote or online?

File your grid with the board in advance, which most jurisdictions require anyway. For a video hearing, keep the PDF open and be ready to share your screen. Walk the board through each comp row by row, same as in person. Sending a clean PDF at least 48 hours ahead lets board members review it before the session, which usually makes for a faster, better hearing.

What if my assessed value is already close to market value but I think the neighboring assessment is lower?

That's an equity argument, not a market value argument. Some states let you appeal on grounds of unequal appraisal: your property is assessed at a higher ratio of market value than comparable properties. Texas Tax Code § 41.43 explicitly allows equity-based appeals. You'd need the assessed values and estimated market values of neighboring properties to build an equalization grid, a different document from a comparable sales grid.

Is there a standard template I can use, or do I have to build the grid from scratch?

No template is universally required, but many county boards publish suggested formats. The Fannie Mae Form 1004 residential appraisal report holds the industry-standard comparable sales grid layout and is freely available online. Copying that structure, even without the full form, gives your grid instant credibility because board members and assessors recognize the format on sight.

How long does it take to prepare a comp grid for an appeal?

Expect four to eight hours for a first-time filer on a residential property. Pulling and verifying sales runs one to two hours. Building and formatting the grid runs one to two hours. Gathering supporting documents, photos, and the assessor's property record card adds another hour or two. If you've done it before or use a pre-built template, you can roughly halve that time.

Sources

1. International Association of Assessing Officers, Standard on the Valuation of Real Property: Most state statutes require assessors to value property at market value, consistent with IAAO's definition of arm's-length market transactions.
2. New York State Department of Taxation and Finance, Office of Real Property Tax Services: New York ORPTS publishes annual sales reports used as public data for comparable sales analysis; RPTL § 524 governs appeal deadlines.
3. International Association of Assessing Officers, Standard on Ratio Studies: IAAO defines arm's-length as a transaction where both buyer and seller are typically motivated, well-informed, and neither is under undue pressure; paired sales analysis is recommended for deriving market-based adjustments.
4. The Appraisal Foundation, Uniform Standards of Professional Appraisal Practice (USPAP): Adjustments above 10 percent of sale price for any single line item, more than 25 percent net, or more than 35 percent gross are red flags indicating a comp is too dissimilar to use reliably.
5. Texas Comptroller of Public Accounts, Property Tax Code § 41.44 and § 41.43: Texas Tax Code § 41.44 sets the appeal deadline as May 15 or 30 days from notice; § 41.43 allows equity-based appeals; Bexar County ARB requires evidence exchange at least 14 days before hearing.
6. National Association of Realtors: Residential appraisal fees typically range from $400 to $700, according to industry practitioner references.
7. International Association of Assessing Officers, Standard on Mass Appraisal of Real Property: IAAO defines acceptable mass appraisal performance as a median assessment ratio between 0.90 and 1.10, with a coefficient of dispersion (COD) below 15 for residential properties in most markets.
8. California State Board of Equalization, Property Tax Rules and Publications: California's property tax lien date (valuation date) is January 1 under the California Revenue and Taxation Code; the standard appeal deadline for most counties is September 15.
9. Illinois General Assembly, 35 ILCS 200/16-55: Illinois statute 35 ILCS 200/16-55 sets the appeal deadline at 30 days from the mailing of the assessment notice.