30 to 60 Percent of U.S. Homes Are Overassessed: And Almost Nobody Appeals

Why overassessment is so common right now

Property tax assessments often lag market conditions, either overshooting when values are rising fast (assessed values based on a hot market stay high even as prices cool) or undershooting when markets spike suddenly. Both directions create errors.

The 2025 data highlights a specific version of this problem: the effective property tax rate on single-family homes rose to 0.9% in 2025, the highest level since 2020, even as home values began softening in many markets. Assessors don't instantly recalibrate. If your area's home values dropped in 2024-2025 but your 2026 assessment is based on 2023 peak values, you may be significantly overassessed.

Common concrete errors that cause overassessment: wrong square footage (county records frequently have incorrect measurements), wrong number of bedrooms or bathrooms, wrong lot size, property coded as being in better condition than it actually is, and failure to deduct for structural problems, proximity to commercial or industrial sites, or other condition factors.

These are not rare edge cases. County assessment records are derived from a mix of data sources, permit records, field visits that happen every several years, third-party data feeds, and they are riddled with errors. A 2024 study of major metro county records found material factual errors in roughly one in five residential assessment records.

What the appeal success data actually shows

The key statistics, sourced from the National Taxpayers Union and Lincoln Institute of Land Policy data:

Between 30% and 60% of US homes are overassessed. Fewer than 3% to 5% of homeowners ever file an appeal. Among those who do appeal, 40% to 60% win some kind of reduction. Successful appeals reduce assessed value by 10% to 15% on average. Professionally prepared evidence, well-documented comparable sales, increases success rates from 30-40% to 60-80%.

The asymmetry here is stark. If roughly half of homes are overassessed and half of appeals succeed, there are tens of millions of homeowners overpaying property tax who could fix it with a few hours of research and a letter. The main barrier isn't the merits. It's inertia and unfamiliarity with the process.

The financial stakes are significant. A 10% reduction in assessed value on a $400,000 home saves $40,000 in taxable value. At a 1.2% effective tax rate, that's $480 per year, compounding until the next reassessment cycle.

How to find comparable sales that win appeals

The evidence that wins property tax appeals is comparable sales data, recent sales of similar homes in your area that support a lower market value than your current assessment.

"Comparable" means: same general neighborhood (assessors weight proximity heavily), similar square footage (within 10-15%), similar age, similar condition, similar number of bedrooms and bathrooms, and sold within the past 6-12 months.

Where to find this data: Zillow and Redfin both show recent sales with details. Your county assessor's website often has a property search tool. The MLS (Multiple Listing Service) data is accessible through a real estate agent if you need it. ATTOM Data and CoreLogic are the professional-grade sources assessors themselves use.

Find 3 to 5 genuinely comparable properties that sold below what your home is assessed at. The gap between your assessment and the comparable sales data is your case. Document each comparable with address, sale date, sale price, and the key features that make it comparable to your property.

The most common mistake in preparing appeal evidence is cherry-picking outliers. Assessors and review boards know their local markets. Use honest comparables that reflect the real market, the gap between assessment and market is usually enough without manufacturing an artificial case.

The appeal process, what to expect

The deadline is the most important thing. Assessment appeals have strict statutory deadlines, typically 30 to 90 days from the date your assessment notice was mailed. The deadline is usually printed on the notice itself. Missing it means waiting a full assessment cycle, typically one to four years depending on your jurisdiction.

The process varies by county but generally follows this pattern: file a written protest or appeal form with your county assessor's office or appeal board, submit your comparable sales evidence, and attend a hearing where you present your case to a review board.

Hearings are typically informal, no lawyers required, no court setting. You present your comparables, the assessor presents their data, and the board issues a decision, usually within a few weeks.

If you win, the reduction applies starting with the current tax year. In many jurisdictions you can also request a refund of prior-year overpayment, though this is subject to the appeal timeline rules.

If the county board denies your appeal, most states have a further appeals process to a state-level board or tax court. But the majority of successful appeals are resolved at the county board level.