Assessments are often wrong. Here is exactly how to challenge yours and win.

Property tax assessments are not gospel. They are estimates — sometimes accurate, sometimes wildly off — made by local government assessors working from limited data, compressed timelines, and imperfect methodology. The National Taxpayers Union estimates that 30% to 60% of residential properties are over-assessed to some degree. If you own real estate, there is a better-than-even chance your assessment is too high.

The good news: every state allows you to appeal. And appeals work. The Institute for Property Taxation reports that informal appeals succeed in reducing assessed value roughly 40% of the time when the homeowner presents credible comparable sales data. Formal appeals succeed at even higher rates when properly documented.

Understanding Your Tax Bill: Assessed Value vs. Market Value

Before you appeal, understand what you are looking at. Your property tax bill is based on the assessed value — not the market value. The relationship between the two varies by jurisdiction, but most states assess at some percentage of market value, typically 80% to 100%. A jurisdiction that assesses at 90% of market value will show an assessed value of $270,000 on a home that would sell for $300,000.

Your goal in an appeal is not to argue what the property is worth today — it is to argue what the assessed value should be based on recent arm's-length sales of comparable properties. These are two different arguments.

Research Comparable Sales

The foundation of any successful appeal is a comparable sales analysis. You need to find three to five properties that recently sold — within the past 12 to 18 months — that are similar to yours in:

Your county assessor's website typically lists recent sales. You can also use public real estate listing records. For each comparable sale, record the sale price, date, and property characteristics. If your subject property has a feature the comparables lack — or lacks a feature the comparables have — note the adjustment you would make.

The standard rule of thumb: comparable properties should be within 0.5 miles and sold within 12 months for residential. For land, the radius expands and the time window tightens because raw land sales are less frequent.

Three Levels of Appeal

1. Informal Review (First Step)

Most jurisdictions start with an informal review. You submit a letter to the assessor's office contesting the value, accompanied by your comparable sales data. There is no hearing — a assessor reviewer simply reconsidered the file. This step is free and often effective. Do not skip it.

2. Board of Assessment Review or Board of Equalization (Formal)

If the informal review does not produce a satisfactory result, escalate to the local board. This is a quasi-judicial body that hears property tax disputes. You will typically submit a formal application and may be invited to present your case in person. Bring:

3. State Tax Court or Circuit Court (Last Resort)

Most property tax disputes never reach this level. If yours does, you will benefit from an attorney specializing in property tax appeals. The cost-benefit threshold here is typically disputes involving properties valued over $500,000 where the assessment error exceeds $20,000.

Common Mistakes to Avoid

The most common reason appeals fail: homeowners argue market value in a market-value forum without understanding that they need to argue assessed value relative to comparable assessed values — not sale prices. Assessors and boards are looking for comparisons to other assessed values in the jurisdiction, not to what properties are selling for on the open market.

Other mistakes: missing filing deadlines (typically 30 to 60 days after the assessment notice is mailed), relying on a single comparable sale when the jurisdiction requires multiples, and failing to document physical deficiencies that justify a lower value.

Timelines by State

Property tax appeal deadlines vary significantly. Texas homeowners have until May 31 or 30 days after the notice is mailed — whichever is later. New York requires filing within 30 days of the notice. California allows 60 days. Many states have different deadlines for unsecured personal property vs. real property.

Find your state's specific deadlines at your state department of revenue website, or call the assessor's office and ask: "What is the deadline to file a property tax appeal?" Write it down. Missing the deadline means you pay the assessment and wait for the next cycle.

The Numbers Game

A $20,000 reduction in assessed value, in a jurisdiction that taxes at 1.5% of assessed value, saves you $300 per year in property taxes. Over a 10-year holding period, that is $3,000. A successful appeal on a $1 million commercial property that reduces assessed value by $100,000 saves $1,500 annually — $15,000 over a decade. The effort is the same whether you win $300 or $15,000. Pick your battles, but do not assume you cannot win.