Comparable Sales Analysis: The Science Behind Property Tax Protests
Written by RedTools Research Team, with appraisal-oriented comparable sales methodology review.
Last updated: April 30, 2026
Your property tax assessment is based on what the appraisal district believes your home is worth. That value is determined primarily through comparable sales analysis — the process of comparing your property to similar homes that have recently sold. Understanding how comps work is the key to building a winning tax protest.
What Are Comparable Sales?
Comparable sales (comps) are properties that have sold in the open market within a recent time period and share key characteristics with the property being valued. Tax appraisers and real estate professionals use comps as the primary method for estimating a property’s market value.
The logic is straightforward: if three homes similar to yours sold for $280,000–$300,000 in the past year, your home’s market value is likely in that range, regardless of what the appraisal district says. If your assessment says $340,000, you have a strong argument for a reduction.
How FairValue Selects Comparable Sales
FairValue uses a multi-factor analysis engine to identify the most relevant comparable sales for your property. Each potential comp is scored across four dimensions:
- Geographic Proximity — Properties closer to your home carry more weight. FairValue prioritizes sales within the same subdivision or neighborhood, then expands outward.
- Property Characteristics — Square footage, bedroom and bathroom counts, lot size, and year built are matched against your property.
- Sale Recency — More recent sales better reflect current market conditions. FairValue weights sales from the last 6 months more heavily than older transactions.
- Market Conditions — Local market trends are factored into the analysis. If values have declined since a comp sold, that sale supports an even lower valuation.
Common Comp Selection Mistakes
- Using properties that are too different. Comparing a 1,500 sq ft bungalow to a 3,000 sq ft two-story undermines credibility.
- Ignoring sale dates. Appraisal boards prefer recent sales, typically within the last 12 months.
- Cherry-picking only the lowest values. A credible protest uses a balanced set of comps that genuinely represent the market.
- Not adjusting for features. If a comp has a pool and your home doesn’t, the raw sale price isn’t directly comparable.
Example: How Comps Win a Protest
Subject property: 3 bed / 2 bath, 1,850 sq ft, built 2004. Assessed value: $355,000.
| Comp | Sq Ft | Year Built | Sale Price | Sale Date | Distance |
|---|---|---|---|---|---|
| Comp 1 | 1,820 | 2005 | $310,000 | Oct 2025 | 0.3 mi |
| Comp 2 | 1,900 | 2003 | $315,000 | Nov 2025 | 0.5 mi |
| Comp 3 | 1,780 | 2006 | $305,000 | Sep 2025 | 0.7 mi |
| Comp 4 | 1,870 | 2004 | $320,000 | Dec 2025 | 0.4 mi |
Average comp sale price: $312,500. Assessment: $355,000. Over-assessment: $42,500 (12%). At a 2.5% tax rate, this costs the homeowner $1,062.50 per year in excess taxes.
Methodology References
- Appraisal Institute
- International Association of Assessing Officers (IAAO)
- Harris Central Appraisal District
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