What time period should comparable sales come from for a property tax appeal?

Last updated 2026-07-11

Why does the comp sale date matter so much for an appeal?

An assessor's job is to estimate what your home would have sold for on one specific date: the assessment date (sometimes called the lien date or valuation date). That date is fixed by state law, and it anchors everything. Walk into a hearing with a sale from two years before that date and the board will tell you it reflects a different market, then set it aside.

This isn't bureaucratic gatekeeping. Property values genuinely shift over months. A sale from January 2022 tells you nothing reliable about value in January 2024 if the market moved 15 percent in between. The time-period rule exists so both sides argue from the same snapshot of the market.

Miss the window and you lose your strongest evidence. The assessor's appraiser, who does this every day, will name the date problem in the first minute. So before you pull a single comp, learn your state's allowed sale-date window.

What is the standard time window allowed for comparable sales?

The honest answer: it varies by state, and sometimes by county or appeal board inside a state. But the most common rule, followed by the majority of state property tax statutes and by the Uniform Standards of Professional Appraisal Practice (USPAP) guidance that most assessors follow, is sales within 12 months before the assessment date ^[1].

Some states allow a 24-month lookback when the market is thin and recent sales are scarce. A handful require something tighter. California's State Board of Equalization guidance, for example, generally points appraisers to a 90-day to 12-month window centered on the lien date of January 1 ^[2]. Illinois county boards of review tend to accept sales within 12 months of the assessment date, which in Cook County is January 1 of the tax year ^[3].

Post-assessment-date sales are trickier. Many states allow them as confirming evidence but won't let them override pre-assessment-date comps. A small number of states, including Georgia, permit post-date sales in the year following the assessment date as direct evidence of value on the appeal date ^[4].

The table below shows the window for several high-population states. Check the specific statute for your county before building your comp set.

State	Assessment Date	Sale Window (typical)	Authority
California	January 1	90 days to 12 months prior	Cal. Rev. & Tax. Code §401; SBE guidance
Illinois (Cook County)	January 1	12 months prior	35 ILCS 200/1-55
Texas	January 1	12 months prior (24 months if thin market)	Tex. Tax Code §23.013
Georgia	January 1	Within the appeal year (pre and post)	O.C.G.A. §48-5-299
New York (NYC)	January 5	12 months prior; post-date allowed as secondary	NYC Finance Dept. guidance
Minnesota	January 2	12 months prior	Minn. Stat. §273.11

How do I find out my state's exact allowed sale-date window?

Three sources get you there fast.

First, look up your state's property tax code. Search "[state name] property tax code valuation" or "[state name] ad valorem tax statute." You want the section on "market value" or "true cash value." Texas Tax Code §23.013, for instance, states the appraisal district "may use" sales from the preceding 24 months if sales in the preceding 12 months are insufficient, which sets a clear two-tier rule ^[5].

Second, download the instructions for your specific appeal board. County boards of review and state tax tribunals publish hearing rules that often spell out the comp window more plainly than the statute does. Cook County's Board of Review publishes filing instructions each appeal year that specify the acceptable sale-date range ^[3].

Third, call the county assessor's office and ask directly: "What sale-date range do you use for residential comparable sales?" The answer also tells you what the assessor's own appraiser will use against you at the hearing. You give away nothing by asking.

If your state allows a 24-month window but only when recent sales are thin, document that thinness. Keep a record of your MLS or public records search showing how few sales occurred in the neighborhood during the standard 12-month period. That record becomes part of your file.

Should I use sales before or after the assessment date?

Before the assessment date is almost always the primary answer. Every mass-assessment approach targets value as of a fixed historical date, so the market evidence logically comes from before that date.

Pre-assessment sales carry more weight because they reflect what buyers actually knew and paid in the market your assessor used. If the assessor set your 2023 value from January 2023 conditions, a sale from October 2022 is directly on point.

Post-assessment sales help when they confirm a downward trend. If your assessment date is January 1 and your hearing is in September, a sale of a genuinely comparable property in June can support your case that value was already declining. Georgia's statute is friendly here: O.C.G.A. §48-5-299 requires the board to consider evidence of value "as of the date of the appeal" in addition to the assessment date ^[4]. Most other states treat post-date sales as secondary.

One trap to avoid: if the market rose sharply after your assessment date, don't accidentally cite post-date sales that show higher values. The assessor will thank you for it.

What counts as a comparable sale besides the date?

Date is one dimension. A sale from the right period is useless if the property is nothing like yours. The standard appraisal framework looks at five things: location, physical characteristics, conditions of sale, financing, and market conditions (the time adjustment) ^[1].

Location means within your neighborhood first, then expanding outward to similar neighborhoods only if needed. Physical characteristics mean square footage, lot size, age, condition, and bedroom/bath count within roughly 15 to 25 percent of your home's specs. Conditions of sale means arm's-length transactions, not foreclosures, estate sales, or sales between relatives unless you adjust for those conditions.

Financing matters less now than it did in the 1980s, but seller-financed deals at below-market rates can inflate apparent sale prices and distort your comp set.

Market conditions is where the date issue loops back in. If your comp is from 10 months before the assessment date and the market moved 5 percent in that span, a properly prepared appraiser applies a time adjustment to that sale. You can do this too. The math is plain: divide the market movement percentage by 12 and multiply by the number of months between the sale and the assessment date. Just be honest about the direction of that adjustment. Don't pretend prices moved down if they moved up.

How many comparable sales do I need?

Three to five is the working standard for residential appeals, and that matches what appraisers actually use under USPAP guidance ^[1]. The idea is that any single sale might be a fluke. Three or more sales that cluster around a lower value are much harder to dismiss than one outlier.

For a typical single-family home appeal, bring five comps if you can: three that are tight matches on location and size, and two that slightly stretch the search (a little bigger, a little farther) but still support your position. If all five point to a value below your assessment, that's a pattern the board has to reckon with.

In a thin market (rural areas, unusual property types), the rule flexes. One or two very well-matched sales can beat five mediocre ones. Document your search, show the board you looked hard, and explain why the market doesn't produce more data.

Commercial appeals are different. You may need five to ten sales and will almost certainly also need income data and a capitalization rate analysis. Commercial appeals at boards like Cook County Tax Assessor or LA County Property Tax often require a full appraisal report, more than a comp sheet.

What if there are no sales in my neighborhood during the allowed window?

This happens, especially in rural counties and tight-knit subdivisions where turnover is low. You have a few options.

Expand geography. Move outward from your immediate neighborhood to similar subdivisions or rural areas with comparable land use and characteristics. Document why those sales are comparable despite the distance.

Use the full 24-month window if your state allows it. Texas explicitly permits this when the 12-month pool is insufficient ^[5]. California appraisers also widen the search window when nearby recent sales are rare.

Switch approaches. The sales comparison approach is not the only way to challenge an assessment. The cost approach (what it would cost to replace the structure minus depreciation, plus land value) and the income approach (for rental properties) are both valid. In many states, presenting any credible methodology that produces a lower value is enough to shift the burden of proof back to the assessor.

Pull a neighborhood sales report from your county assessor's public records. Many counties now publish recent sales online by neighborhood or subdivision. Montgomery County Property Tax records, for instance, are searchable online and let you filter by sale date and location. Use those records to show the board you did a thorough search.

Does the allowed sale window change if the market shifted dramatically?

This is a real and underappreciated issue. During the 2020 to 2022 run-up, assessors in many counties used sales from a fast-rising market to justify big increases. Homeowners who appealed with older, cheaper sales from 2019 often got told those sales were too stale.

The flip side matters now. In markets that cooled or declined through 2023 and 2024, sales from right before the assessment date may show lower prices than the assessor assumed. There, the recency of your comps works in your favor.

Some states responded to volatility by writing clearer rules. Minnesota's statute at Minn. Stat. §273.11 anchors value to January 2 of the assessment year, and the Minnesota Tax Court has consistently required that comp sales reflect conditions as of that date, not conditions from an earlier boom or bust ^[6].

If the market moved sharply during your allowed window, apply a time adjustment to bring every comp to the assessment date. Don't cherry-pick comps from the single cheapest month in the window. Boards see that tactic constantly, and it wrecks your credibility.

One clean, citable stat: the Federal Housing Finance Agency House Price Index showed U.S. home prices rose 28.6 percent from Q1 2020 to Q1 2022, then declined in many markets through Q3 2023 ^[7]. If your assessment was set mid-2022 using peak comps and you're appealing with post-peak 2023 data, that FHFA dataset is public evidence of the market shift.

How do I organize and present my comp evidence at the hearing?

Format matters. A board member reviewing 40 appeals in a day responds to a one-page grid, not a stack of MLS printouts.

Build a comp grid with these columns: address, sale date, sale price, square footage, price per square foot, number of bedrooms and bathrooms, lot size, and notes on any adjustments you made. Put your subject property in the first row. The visual message should read at a glance: here are four sales from within the allowed window, and their adjusted values sit below my assessed value.

Make sure every sale shows the recorded sale date, not the contract date or the listing date. Boards care about the recorded date because that's what shows up in the county's official records. If a sale closed December 20 but the county recorded it January 10, verify which date your board uses.

Attach the public records source for each sale. In most counties you can print or screenshot the deed recording from the county recorder's website or the assessor's online portal. That sourcing tells the board you're using verified data, not Zillow estimates.

If you're doing a DIY appeal, TaxFightBack's appeal kit walks through building this exact grid with state-specific sale-date windows pre-filled, so you don't have to decode each statute yourself.

For county-specific hearing procedures in large jurisdictions like Bexar County Tax Assessor or Gwinnett County Tax Assessor, check the assessor's website for any required submission forms, because some counties have specific comp submission templates.

Can the assessor reject my comps if they're from the right time period?

Yes. A valid sale date is necessary but not sufficient. The assessor or board can still argue your comps aren't truly comparable on physical characteristics, location, or conditions of sale.

Common objections to prepare for: the comp had a pool yours doesn't (or the reverse); the comp was a distressed sale; the comp sits in a different school district or tax district; the comp has substantially more or less square footage.

For each objection, you need either a counterargument or an adjustment. If your comp is 10 percent larger, acknowledge it and apply a downward adjustment to the sale price. A simple dollar-per-square-foot adjustment usually does the job for residential properties. Show your math.

The assessor's appraiser will bring their own comps, often from the same time window but picked to support the assessment. Don't be surprised. Study their comps in advance if you can get them (some counties release the assessor's evidence before the hearing). Look for weaknesses: are their comps farther away, bigger, or in better condition than yours? Flag those differences at the hearing.

Keep your tone factual. You're making an argument about market data, not accusing anyone of wrongdoing. Boards respond to calm analysis, not frustration.

What resources let me find sale dates and prices for free?

Most county recorder and assessor offices now post recent sales online, often searchable by date range, address, or subdivision. That's your first stop. Examples: the Los Angeles County Assessor portal at assessor.lacounty.gov lets you search recent sales by tract ^[8]. The New York City Department of Finance publishes the Rolling Sales files for all five boroughs, updated quarterly, with sale dates and prices for every arm's-length transaction ^[9].

For states where the county assessor lacks a strong portal, try the state's GIS property data portal. Many states keep a central repository of deed transfers.

Zillow, Redfin, and Realtor.com show recent sales, but their dates are sometimes the list date or contract date rather than the recorded sale date. Always cross-reference against the county's recorded deed data when you build an official comp set for a hearing.

The National Association of Realtors publishes median sale data at the metro level, useful for a market-trend argument but not for verifying individual comps ^[10]. The FHFA House Price Index, available at fhfa.gov, gives quarterly price-change data by metro area and census division, which can support a time-adjustment calculation ^[7].

For Santa Clara Property Tax or Hennepin County Property Tax appeals, each county runs its own searchable sales database. Linking directly from those county assessor sites gives you citable, official sale records a board can't dispute as a source.

What mistakes do homeowners most often make with comp sale dates?

The single most common mistake is using the listing date instead of the closing or recorded date. A home listed in October 2022 but closed in December 2022 has a recorded sale date of December 2022. If your window ends November 30, 2022, that sale is out.

Second most common: assuming Zillow's "sold" date is the recorded date. It often isn't. Always pull the deed from the county recorder.

Third: using sales from a neighboring city or zip code without explaining why they're comparable. Geographic proximity alone isn't enough. You have to show the neighborhoods share similar characteristics.

Fourth: picking the three cheapest sales in the window without regard to comparability. This is the easiest attack for an assessor's appraiser. Your comp set should hold up on all five dimensions, not price alone.

Fifth: not knowing whether your state allows post-assessment-date sales as primary evidence. If Georgia allows it and you're in Georgia, leaving post-date sales out of your packet is leaving ammunition on the table ^[4].

The TaxFightBack appeal kit includes a comp checklist that flags these errors before you submit, which helps most if this is your first appeal and you're working without an appraiser.

Frequently asked questions

How far back can comparable sales go for a property tax appeal?

In most states, 12 months before the assessment date is the standard cutoff. Texas and some other states extend to 24 months when the 12-month pool has too few sales. A handful of states, like Georgia, also allow sales from after the assessment date. Check your state's property tax code for the exact rule before pulling comps.

Can I use sales from after my assessment date as comparable evidence?

Sometimes. Georgia's statute explicitly allows post-assessment-date sales as primary evidence. Most other states treat them as secondary, confirming evidence only. If the market dropped after your assessment date, post-date sales are worth including, but lead with your pre-date comps and frame the post-date sales as further confirmation of value.

What if no homes in my neighborhood sold in the allowed time window?

Expand your search geographically to similar nearby neighborhoods and document your search so the board can see you tried. If your state allows a 24-month window when data is thin, invoke that. You can also switch to a cost approach or income approach instead of the sales comparison method. Either of these can be a valid basis for a lower assessed value.

Does the type of sale matter, or just the date?

Both matter. The date must fall in the allowed window, but the sale also needs to be an arm's-length transaction: a willing seller, a willing buyer, neither under pressure. Foreclosure sales, bank REO sales, estate sales, and sales between relatives are typically not arm's-length and need to be flagged or excluded. A valid date on a distressed sale still makes a weak comp.

How do I apply a time adjustment to a comp that's eight months old?

Find the percentage change in your local market over the period between the sale date and the assessment date, using a verifiable index like the FHFA House Price Index. Divide that percentage by 12 and multiply by 8 to get the eight-month adjustment. Apply that percentage to the sale price. If prices fell 6 percent annually, your time adjustment is minus 4 percent for eight months. Show the math in your comp grid.

Is there a minimum number of comparable sales required for an appeal?

No state statute sets a hard minimum for informal or formal board appeals. USPAP guidance used by appraisers recommends enough sales to support a credible value conclusion, typically three to five for residential property. Bringing fewer than three is risky because one atypical sale can be dismissed. Five well-matched comps that all point lower than your assessment is a strong package.

How does the assessment date differ from the appeal deadline?

The assessment date is the valuation date, the market snapshot your assessor used. It's typically January 1 of the tax year in most states. The appeal deadline is the cutoff to file your appeal, usually 30 to 90 days after you receive the assessment notice. Your comp sales must fall within the window before the assessment date, not before the appeal deadline, so these are two separate dates to track.

Can I use a sale of my own property as evidence in an appeal?

Yes, and it can be your strongest single piece of evidence if the timing works. If you bought your home in an arm's-length sale within the allowed window before the assessment date and paid less than the assessed value, that sale is direct market evidence of value. Bring the recorded deed and the closing disclosure. Boards generally give significant weight to a recent arm's-length purchase price.

What happens if my comparable sales are from a different school district?

The assessor may argue they're not comparable because different school districts can affect buyer behavior and prices. You can counter this if you show the neighborhoods are otherwise similar and the school districts have comparable ratings. Ideally, keep comps within the same school district. If the market is thin and you must cross district lines, acknowledge it and explain your reasoning.

Do online estimates like Zillow count as comparable sales evidence?

No. Zillow's Zestimate and similar algorithmic estimates are not sales. They're models, and boards know it. What Zillow does offer is a list of recent sold properties with dates, which you can then cross-reference against county recorder data. Use Zillow to find candidates, but source every comp you actually submit from the county's official deed or sales records.

Does the 12-month rule apply to commercial property appeals too?

Yes, the same general framework applies, but commercial appraisers also weight income capitalization heavily. A commercial board hearing will want comps within 12 months of the assessment date for the sales comparison approach, but the income approach using current rent rolls and cap rates often carries more weight than comps alone for income-producing properties. Check the specific rules for your jurisdiction.

What's the difference between the assessment date and the lien date?

In most states these are the same thing or very close. California explicitly calls January 1 the lien date, and it also functions as the valuation date. Texas uses January 1 as the assessment date. A few states assess at different times of year, like New York City's January 5 taxable status date. Check your state's statute; the valuation date anchors your comp window regardless of what it's called.

Can I hire a licensed appraiser to select comps for me, or do I need to do it myself?

You can always hire a licensed appraiser to produce a full appraisal report, which includes comp selection. For most residential appeals under $50,000 in assessed value, that cost ($400 to $800 for a full appraisal) may outweigh the tax savings. DIY comp research using county records, organized into a clear grid, is accepted at most residential board hearings without requiring a licensed appraiser's signature.

Sources

1. Appraisal Foundation, USPAP 2024 Edition (Standards Rule 1-4): USPAP requires appraisers to analyze comparable market data and make adjustments for differences; the sales comparison approach relies on arm's-length transactions from the relevant market period.
2. California State Board of Equalization, Assessors' Handbook Section 501 (Basic Appraisal): California SBE guidance directs assessors to use sales data centered on the January 1 lien date, generally within a 90-day to 12-month window, expanding when the market is thin.
3. Cook County Board of Review, Appeal Filing Instructions: Cook County Board of Review publishes annual filing instructions specifying the acceptable sale-date range for comparable sales submitted in residential appeals.
4. Georgia General Assembly, O.C.G.A. §48-5-299: O.C.G.A. §48-5-299 requires boards of equalization to consider evidence of value as of the appeal date, permitting post-assessment-date sales as primary evidence in Georgia appeals.
5. Texas Legislature, Texas Tax Code §23.013: Texas Tax Code §23.013 states that the appraisal district may use sales from the preceding 24 months if sales in the preceding 12 months are insufficient to determine market value.
6. Minnesota Legislature, Minn. Stat. §273.11: Minnesota Stat. §273.11 anchors property value to January 2 of the assessment year; Minnesota Tax Court requires comp sales to reflect market conditions as of that date.
7. Federal Housing Finance Agency, FHFA House Price Index: FHFA HPI data showed U.S. home prices rose 28.6 percent from Q1 2020 to Q1 2022 before declining in many markets through 2023, providing a publicly citable basis for time adjustments.
8. Los Angeles County Assessor, Property Search Portal: The LA County Assessor's portal allows users to search recent sales by tract and sale date, providing official recorded sale data for comp research.
9. New York City Department of Finance, Rolling Sales Data: The NYC Department of Finance publishes quarterly Rolling Sales files for all five boroughs, listing recorded sale dates and prices for arm's-length transactions.
10. National Association of Realtors, Research and Statistics: NAR publishes median sale price data at the metro level, useful for demonstrating market trends in an appeal but not a substitute for individual recorded sale data.
11. Illinois Compiled Statutes, 35 ILCS 200/1-55: 35 ILCS 200/1-55 establishes assessment standards in Illinois; Cook County assessments are anchored to January 1 with a standard 12-month sale-date window for comparable evidence.