Every fall I hear the same sentence from Seattle homeowners: my assessed value went down and my tax bill still went up. They read the notice twice, sure the County made an error. The County did not make an error. The bill and the value are set by two different machines, and they move in different directions more often than people think.
The short version: your tax is your value multiplied by a levy rate, and the levy rate is decided by voters and budgets, not by what your house is worth. When the rate climbs faster than the value falls, the bill climbs. King County says it outright — voter-approved measures, and not increasing property values, are responsible for increases in property taxes.
Two machines, one bill
There are two numbers on your statement, and only one of them has anything to do with your house. The assessed value is the County's estimate of market value, updated every year. The levy rate is the consolidated tax rate your local governments need to fund their budgets and the measures voters approved. The bill is the product of the two, and King County spells out the formula on its residential property tax page:
Assessed value ÷ 1,000 × levy rate = your tax. An increase in value does not mean a dollar-for-dollar increase in tax — and a decrease in value does not mean a dollar-for-dollar decrease, either.
For a standard Seattle parcel, levy code 0010 carries a 2026 rate of $9.90845 per $1,000 of assessed value. A house assessed at $800,000 produces about $7,927. If next year the value drops to $760,000 but the rate climbs to $10.45 — because a school levy or a transit measure passed — the bill comes to $7,942. Value down 5%, bill up. The math is that simple and that unforgiving.
This is not a Seattle quirk. The state's whole property-tax design works this way, which is why the Assessor's office keeps the disclaimer front and center: value and tax do not move in lockstep.
Before you blame the rate, check the record it was computed from. The Assessor's eReal Property search lists the square footage, bedrooms, baths, condition, and grade the County used, and those fields carry a mistake more often than you would expect — a bathroom that never existed, a finished-basement square footage counted twice, a condition grade that overstates the interior. A wrong characteristic produces a wrong value, and getting it corrected through the Assessor's office at 206-296-7300 is faster than a full appeal.
The appeal kit builds your deadline from your own valuation notice, your assessment at a glance, comparable sales from your King County record, and a draft Board petition you file free through eAppeals.
Where the increase actually comes from
The rate goes up when local governments ask for more, and Seattle keeps asking. The 2026 consolidated rate includes the state school levy, county and city levies, and a stack of voter-approved measures for veterans, seniors, fire protection, and parks. King County's 2026 tax breakdown is blunt about it: the voter-approved measures are what push the bill up, not the value of the land under it.
King County keeps only about 20% of the money. The rest passes through to the state, the city, and the school and fire districts. So when the bill jumps, the County is usually the messenger, not the beneficiary — which is also why arguing with the collector does nothing for you.
The County is the collector, not the spender. Most of the bill passes through to other taxing districts — which is why the only number you can actually fight is the value, not the rate.
Source: King County Assessor, "Where do my property tax dollars go?" (2026).
A 5% value drop can be swamped by a rate increase. This is a worked example, not a specific parcel — but the direction is the same across the city, which is why some owners saw bills rise on a flat or falling value.
Source: levy formula from King County residential property tax guidance; Seattle code 0010 rate $9.90845 per $1,000 (2026). The rate change is illustrative.
The one lever you actually have
You cannot vote the levy rate down on your own, and you cannot negotiate the budget. The only number on the statement you can contest is the assessed value — and that is exactly what the appeal process exists for. If the County's value estimate is high relative to what your house would actually sell for, you can argue it down, and a lower value lowers the bill no matter what the rate does.
The window is short and it is tied to your notice, not the calendar. Under RCW 84.40.038, you file by July 1 of the assessment year, or within 60 days of the mailing date on your valuation notice — whichever is later. King County's Board of Appeals and Equalization says about a quarter of the values people appeal get a reduction. The argument has to be market value — comps, your own sale history, an appraisal — not the size of your bill.
If the value on your notice looks wrong, pull three comparable sales and file. The evidence has to be market value — not the size of the bill, not hardship — and the County's own guidance says roughly a quarter of appealed values end up reduced. The full playbook — the deadline math, the comps that carry the argument, and the packet line by line — is in our King County property tax appeal guide.
The Property Tax Appeal Kit builds a parcel-specific evidence packet and a draft Board petition from your own Assessor record, so you can file free through eAppeals before the 60-day window closes.
When a new build is behind the jump
Sometimes the bill rises for a reason that has nothing to do with the rate: King County picked up new construction on your parcel. Add a finished backyard cottage, and the Assessor books its value on the next roll. That is a value increase, not a rate increase — and it is also the single most common reason a Seattle homeowner's bill climbs in a year the neighborhood as a whole looked flat.
Our DADU property tax guide runs the exact numbers on when the County books a cottage and what it adds to the bill at the code 0010 rate. If you are weighing whether to build one in the first place, the free homeowner checklist starts from the lot side, and the pre-approved plan path is worth knowing if you want to keep the project simple. For a read on what a build might add to your own parcel's value and tax, the customized feasibility report measures your address from City and County records — the same levy code, lot, and structure data the Assessor is working from.
"Homeowners chase the assessor, but the assessor didn't set the rate. The voter did. The only number you can fight is the value — so fight that number, with comps, inside the 60 days. Everything else is yelling at the mailman."
Bob's takeIf you are deciding whether to add a cottage, the tax line is just one row in a longer sheet — the same sheet that runs the rent roll and the resale value. The neighborhood profiles measure the lot and hazard conditions that decide whether a build pencils out in Green Lake, West Seattle Junction, or anywhere else, and the customized feasibility report measures your own lot's build potential and levy code. The Seattle DADU Pro Guide covers the full sequence for free, and the September housing market note puts the current value picture in one place.
Frequently asked questions
Why did my Seattle property tax go up when my assessed value went down?
Because the bill is value divided by 1,000, times a levy rate set by local budgets and voter-approved measures — not by your home's value. When the rate rises faster than your value falls, the bill still climbs. King County says voter-approved measures, not increasing values, are responsible for most increases.
How is Seattle property tax actually calculated?
Assessed value divided by 1,000, multiplied by the consolidated levy rate. A standard Seattle parcel uses levy code 0010 at $9.90845 per $1,000 in 2026, so every $100,000 of value produces about $991 of annual tax.
What can I do if I think my King County assessment is too high?
Appeal it. File free through eAppeals or by mail to the Board of Appeals and Equalization by July 1, or within 60 days of your notice's mailing date, whichever is later. About 25% of appealed values get a reduction.
Does a lower home value automatically mean a lower tax bill?
No. The bill only falls if the levy rate stays flat or drops too. As voter-approved measures have pushed Seattle's consolidated rate up, a modest value drop can be more than offset by the rate — exactly why some bills rose as values flattened or fell.
This article is educational and preliminary. It is not legal advice, tax advice, or appraisal advice. The worked example uses the 2026 Seattle levy code 0010 rate of $9.90845 per $1,000; the value-drop and rate-change figures in that example are illustrative, not a specific parcel. Levy rates and Board procedures change; verify everything against current King County and RCW text before you file.