If you own a home in King County, Washington, you have a constitutional right to challenge the value the Assessor assigns to your property each year. The process — appealing to the King County Board of Equalization (BOE) — is free, designed for self-represented homeowners, and runs on a hard annual deadline. This guide walks through every step.

The deadline: July 1, or 60 days after your value notice

Your appeal petition must be postmarked, hand-delivered, or filed online by the later of two dates: July 1 of the assessment year, or 60 days from the mailing date printed on your official value notice. The Assessor mails notices between May and November, so check yours carefully — your deadline may be later than July 1.

Miss the deadline and you forfeit your appeal right for the entire assessment cycle. File at least a week early to leave time for processing issues.

What you can appeal

You can appeal the Assessor's determination of true and fair market value of your property as of January 1 of the assessment year. You cannot appeal:

  • The property tax rate (set by the various taxing districts)
  • The total amount of your tax bill (a function of value × rate)
  • School levies or voter-approved measures

The only thing on the table is whether the assessed value exceeds what your home would actually sell for on the open market.

Step 1: Read your property record card

Pull your property record from the King County Assessor's eReal Property database. Common errors that justify a reduction:

  • Wrong square footage of living area
  • Incorrect bedroom or bathroom count
  • Wrong year built or grade
  • Building condition listed too high (no recent updates, deferred maintenance)
  • Lot size off

Step 2: Build your comparable-sales analysis

The strongest evidence in nearly every King County appeal is comparable sales — recent arms-length transactions of similar nearby homes that sold for less than your assessed value. The county's own eSales tool publishes these. Pick 3–5 comps from the year ending January 1 of the assessment year, ideally:

  • Same neighborhood / school district
  • Similar living area (within ~20%)
  • Similar age, grade, and condition
  • Sold within 6–12 months of the valuation date

Adjust each comp for differences (size, age, condition, view, lot). The average of the adjusted prices is your supportable market value. If it's lower than the Assessor's number, you have a case. This site does that analysis automatically from official county data.

Step 3: File your petition

King County offers three filing channels:

  • By mail (recommended): Board of Appeals and Equalization, 500 Fourth Ave, ADM-LJ-0210, Seattle, WA 98104. Send via USPS Certified Mail with Return Receipt — the postmark date is your legal filing date under RCW 1.12.070, and the green return card is your proof of timely filing. About $5 in postage.
  • Online: the King County eAppeals portal. You can file, track status, upload evidence, and respond to the Assessor in one place. Requires creating an account.
  • In person: same address as the mailing option, business hours.

File a separate petition for each parcel. Your petition must state your opinion of value and give specific reasons — "I think it's too high" is not enough. Reference your comps, errors on the property card, condition issues, or any other concrete basis.

Step 4: Evidence exchange (the 21-day rule)

Both you and the Assessor must share any evidence you intend to present with the Board and with each other at least 21 business days before your hearing. Late evidence is excluded. This is also when most appeals settle — the Assessor reviews your comps and often offers a reduction without going to hearing.

Step 5: The hearing

Most hearings are short (15–30 minutes) and informal. You present your evidence, the Assessor presents theirs, the three-member Board panel asks questions. Then they deliberate and you leave. You don't need a lawyer. Decisions are issued in writing within 45 days of the hearing.

If you complete evidence exchange early, you can request an expedited hearing.

If you lose: the second appeal

If you disagree with the BOE's decision, you have 30 days from the mailing date to appeal to the Washington State Board of Tax Appeals (BTA). That's a higher-evidence-bar process — most homeowners stop at the BOE.

What it costs

Filing with the King County Board of Equalization is free. There is no filing fee. Your only investment is the time to pull comps and write a one-page argument — typically 1–2 hours.

Realistic outcomes

National data from the National Taxpayers Union Foundation puts the success rate for filed appeals at 40–60%, with successful appeals shaving 8–20% off assessed value. At King County's ~1.0% effective tax rate, a 10% reduction on a $1M home saves roughly $1,000/year — and that lower value becomes the baseline for future years, so the savings compound. See the full math here.

Next step

Pull your free report — it gives you the assessed-value history, comparable sales, and the data you need to decide if you have a case before you write a single word of your petition.