This is the distinction that turned my anger into an actual plan. Assessed value and market value are two different numbers, and the difference between them is the whole game.

Market value is what your home would actually sell for today. It moves constantly. It's the Zillow-and-Redfin number, the "what did the place down the street go for" number.

Assessed value is the Assessor's estimate of your market value as of January 1 of the assessment year, produced by a model running over hundreds of thousands of properties. No human walked yours. In a rising market that estimate tends to lag behind reality. In a fast-moving or falling market, it can overshoot — badly.

Assessed value is not sale price. It's a computer's guess about your house on one specific day. Guesses can be wrong, and wrong is appealable.

That gap — assessment sitting above what your home is really worth — is exactly what an appeal targets. In my case the gap was not subtle. The county said about $1.4 million. The appraisal my bank ordered when I bought the place came in around $1,000,000. That's not a rounding error. That's a case.

And I'm not a special case. I checked every King County home that sold in 2025 against the value the county gave it for January 1, 2026. About one in six is now assessed above the price it actually sold for — a price set by a real buyer, months before the valuation date.

Histogram of King County homes sold in 2025: assessed value as a share of sale price. Most are assessed below their sale price; 15.5% are assessed above it.
15,879 King County homes sold in 2025 (valid market sales). Assessed value = the county's January 1, 2026 value. Source: King County Assessor public data.

The January 1 rule (read this before you get excited)

The county values every home as of January 1, and that's the only date the Board of Equalization cares about. Two consequences:

  • What counts: sales of similar homes close to January 1. If those sold for less than your assessment, that's a case.
  • What doesn't: the market softening in, say, May. You can't appeal this year's number on that. It shows up in next year's assessment — which is exactly when you should check again.

How to check the gap yourself

  1. Find your assessed value. It's on your value notice, or look up your parcel on the King County Assessor's site.
  2. Find 3–5 comparable sales. Similar size, age and style, within about half a mile, sold as close to January 1 as you can get.
  3. Compare. If the typical comp sold meaningfully below your assessment, you probably have an appeal. If they sold above it, you probably don't — unless the county has your square footage wrong or the house has problems a model can't see.

Or skip the spreadsheet: the free check does steps 1–3 against 57,000+ recent King County sales, and says so if your assessment is fair.

If the gap is real, you have the same opening I did. Here's how to appeal it, step by step.