Rob Hartley

Founder, AppealDesk · February 16, 2026

How to Find Comparable Sales for Your Property Tax Appeal

Updated February 2026 · 12 min read

Why Comparable Sales Win Property Tax Appeals

County assessors determine your property’s value using mass appraisal — algorithms that estimate thousands of properties at once. These algorithms look at the same data you’re going to find: recent sales of similar homes. The difference is that mass appraisal can’t account for every property’s unique characteristics. When you find comparable sales that sold for less than your assessed value, you’re showing the review board that real market transactions don’t support their number.

According to the IAAO Standard on Mass Appraisal, the sales comparison approach is the primary method for residential property valuation. Review boards expect comparable sales evidence because it mirrors their own methodology. Arguments based on opinion, tax burden, or affordability — while understandable — don’t meet the evidentiary standard.

Comparable sales are just one of three types of evidence review boards accept. For the complete picture—including property condition documentation and assessment errors—see our guide on what evidence you need for a property tax appeal.

What Makes a Strong Comparable Sale

Not all sales are equally useful. Here’s what county review boards look for in a credible comparable:

Where to Find Comparable Sales: 6 Sources

1. Your County Assessor’s Website (Free)

Most county assessors publish recent sales data online, often in a searchable property database. Look for “recent sales,” “sales search,” or “property transfer records.” This is the most authoritative source because it’s the same data your assessor used. The downside: interfaces are often clunky, data may lag 2-3 months behind actual closings, and not every county publishes sale prices (some non-disclosure states like Texas don’t require it).

2. Zillow Sold Listings (Free)

Use Zillow’s map view and filter to “Sold” listings within the last 6-12 months. You’ll see sale prices, square footage, bedroom/bathroom counts, and lot sizes. Important: Use the sold prices, not the Zestimate. Zestimates are algorithmic guesses and are not accepted as evidence by any review board. The actual recorded sale price is what matters.

3. Redfin Sold Data (Free)

Redfin often has more detailed listing data than Zillow, including original listing price, days on market, and price reductions. The “Sold” filter on their map view is intuitive. Redfin also provides a downloadable CSV of recent sales in some markets — useful if you want to do your own analysis in a spreadsheet.

4. Realtor.com and Public Records (Free)

Realtor.com pulls from MLS data and includes recently sold properties with photos, price history, and property details. Some counties also maintain separate deed recording or transfer tax databases accessible through the county clerk or recorder of deeds office.

5. Ask a Real Estate Agent (Free, Sometimes)

Licensed agents have access to the local MLS (Multiple Listing Service), which contains the most comprehensive and accurate sales data available. If you have a relationship with an agent — your buyer’s agent from when you purchased, for example — they can often pull comparable sales as a favor. MLS data includes details not found on public sites: interior photos at time of sale, agent remarks about condition, concessions, and whether the sale was arm’s-length.

6. Professional Evidence Services ($49+)

Services like AppealDesk automate the comparable sales research process. For $49, AppealDesk identifies the strongest comps from professional databases, calculates price-per-square-foot adjustments, verifies your county’s assessment ratio, and formats everything into an evidence packet ready for your review board. This saves 15-40 hours of DIY research.

How Many Comparable Sales Do You Need?

Three is the minimum. Five is ideal. Here’s why: one comp can be dismissed as an outlier. Two comps can be dismissed as selective. Three comps establish a pattern. Five comps give you room to lose your weakest one or two and still maintain a strong case.

Avoid submitting more than 6-7 comps. Review boards have limited time, and a bloated evidence package can dilute your strongest data points. If you have 10 possible comps, select the 5 that most clearly support your case.

How to Adjust Comparable Sales for Differences

No two homes are identical. The goal is to account for differences between your property and each comp so you’re comparing apples to apples. There are two approaches:

Simple Method: Price Per Square Foot

Divide each comp’s sale price by its square footage. This gives you a price-per-square-foot figure that normalizes for size differences. If your five comps sold at $150, $145, $155, $148, and $152 per square foot, and your county assesses your home at $175 per square foot, you have clear evidence of overassessment.

Example: Your home is 2,200 sq ft assessed at $385,000 ($175/sq ft). Five comparable sales average $150/sq ft. Based on comparable sales, your home’s market value is approximately $330,000 — a $55,000 overassessment.

Advanced Method: Feature Adjustments

Professional appraisers adjust each comp’s price for specific feature differences. If a comp has 3 bedrooms and yours has 4, they subtract estimated value for the extra bedroom. Common adjustments:

• Extra bedroom: +$5,000-15,000 depending on market
• Extra bathroom: +$5,000-10,000
• Garage (2-car vs none): +$15,000-25,000
• Pool: +$10,000-30,000 (varies significantly by region)
• Age difference (per decade): -$5,000-15,000 for older construction
• Condition (good vs fair): +/- $10,000-25,000

For most residential appeals, the price-per-square-foot method is sufficient and easier for review boards to follow. Feature adjustments add credibility but aren’t required.

How to Present Comparable Sales Evidence

Format matters. A disorganized pile of printouts won’t impress a review board. Structure your evidence clearly:

1. Cover letter: One page summarizing your property, your assessed value, your requested value, and the basis for your appeal. See our appeal letter template for structure.
2. Property summary: Your address, assessed value, square footage, bedrooms, bathrooms, year built, lot size, and any condition issues.
3. Comparable sales table: Each comp with address, sale date, sale price, square footage, price/sq ft, bedrooms, bathrooms, year built, and distance from your property. Include a column for adjusted price if you’re making feature adjustments.
4. Map: A simple map showing your property and each comp’s location. This visually demonstrates proximity. Google Maps or a screenshot from Zillow works.
5. Average/median calculation: Show the average or median sale price (and price/sq ft) across your comps, and how it compares to your assessed value.

Don’t Forget the Assessment Ratio

In states that don’t assess at 100% of market value, you need to account for the assessment ratio when comparing your assessed value to comparable sales. For example, if you’re in Georgia (40% assessment ratio) and comparable sales suggest a market value of $300,000, the correct assessed value is $120,000 (40% × $300,000) — not $300,000.

This is one of the most common mistakes in DIY appeals. Homeowners in states like Tennessee (25%), South Carolina (4%), and Alabama (10%) frequently compare their assessed value directly to market sale prices, which makes no sense given their state’s ratio. The IAAO considers assessment ratio analysis fundamental to fair property valuation.

5 Mistakes That Weaken Your Comparable Sales Evidence

1. Using Zestimates instead of sale prices. Zillow’s algorithm-generated estimates are not market data. Only actual recorded sale prices count as evidence.
2. Including distressed sales. Foreclosures and short sales typically sell below market value and most review boards exclude them. Unless your market is dominated by distressed sales (which itself could support a lower value), stick to arm’s-length transactions.
3. Comparing across neighborhoods. A comp in a different school district, across a highway, or in a visibly different neighborhood will be dismissed. Physical proximity alone isn’t enough — the neighborhoods must be comparable in character.
4. Using stale data. Sales from 18-24 months ago don’t reflect current market conditions. In a falling market, old high-price sales actually hurt your case. Prioritize the most recent sales available.
5. Ignoring the assessment ratio. Comparing raw sale prices to your assessed value only works in states with a 100% assessment ratio (Texas, California, etc.). In fractional-assessment states, you must apply the ratio. Learn yours at our assessment ratio guide.

Frequently Asked Questions