Last updated 2026-07-09
TL;DR
King County assesses property at 100 percent of market value every January 1. Your tax bill equals that assessed value times the levy rate for your area. If your value is higher than what your home would actually sell for, you can appeal to the King County Board of Equalization. The deadline is August 1, or 60 days from your notice date, whichever comes later.
What is King County tax assessed value and how is it calculated?
King County assessed value is the county assessor's estimate of your property's fair market value as of January 1 of the assessment year. Washington law requires counties to assess at 100 percent of true and fair value, meaning the price a willing buyer would pay a willing seller when neither is under pressure. [1]
The King County Department of Assessments splits the county into geographic areas it calls "neighborhoods" and revalues each one on a four-year physical inspection cycle, with statistical updates in the off years. [2] That matters. Your value can get updated by a computer model in years when no appraiser ever walked your block. Statistical updates run on sales ratios: the assessor tracks what comparable homes actually sold for and adjusts values county-wide to stay near 100 percent of market. If sales in your neighborhood rose 15 percent but your own house has condition problems those sales don't reflect, the model overshoots.
Your assessed value shows up on your Annual Value Notice, usually mailed in the spring before the tax year. The notice lists land value and improvement value separately. Both are appealable. A lot with a derelict structure can carry an improvement value that should honestly be zero, yet assessors sometimes assign a positive number by default.
King County does not cap annual assessment increases the way some other states do. There is no assessment freeze for most owners under 65. If values in your neighborhood jumped 20 percent in a year, your assessed value can jump 20 percent too, and your tax bill follows right behind it. [11]
How does King County assessed value translate to your actual tax bill?
Your tax bill is assessed value times a combined levy rate. That rate bundles state school taxes, local school levies, county general taxes, city taxes if you live inside a city, fire district levies, library levies, and any voter-approved special levies. Rates swing widely depending on where you live.
For 2024, the average combined levy rate in King County ran roughly $9 to $11 per $1,000 of assessed value, depending on your taxing district, though some areas came in higher. [3] On a home assessed at $800,000, that produces a bill somewhere between $7,200 and $8,800 a year, before any exemptions.
| Assessed Value | Rate (per $1,000) | Estimated Annual Tax |
|---|---|---|
| $500,000 | $9.50 | $4,750 |
| $700,000 | $9.50 | $6,650 |
| $800,000 | $9.50 | $7,600 |
| $1,000,000 | $9.50 | $9,500 |
| $1,500,000 | $9.50 | $14,250 |
These are rough illustrations. Your real levy rate is printed on your tax statement and depends on your address. Here is the number that should get your attention: a $100,000 cut in assessed value saves you roughly $950 to $1,100 a year at typical King County rates. That's real money, and it repeats every year you hold the property.
Washington's state school levy is set by the legislature under the McCleary framework and hits every property in the state. Local levies are voted on by residents and can shift a lot year to year. You can't appeal either one away. But shrinking the base (your assessed value) shrinks every line on the bill.
Why might your King County assessed value be wrong?
Mass appraisal is imprecise by design. The assessor's office handles hundreds of thousands of parcels and can't inspect each one every year. The errors fall into a few predictable buckets.
Condition problems top the list. If your roof leaked for three years, the kitchen is original 1970s, or a foundation crack has been there since you bought the place, the statistical model has no idea. The comparable sales that pushed your value up may all have been renovated homes. Your unrenovated house isn't worth what those sold for, but the model treats you the same.
Data errors come second. The assessor's records might show three bathrooms when you have two, or count finished square footage that's really a garage or an unfinished basement. Every over-counted square foot inflates your value. Pull your property detail record from the King County Assessor's website and read every field. [2]
Market timing is third. Values are locked as of January 1. If sales in your neighborhood were unusually hot in the months the assessor sampled, then the market cooled before your notice landed, your assessed value may already sit above current reality.
Uniformity errors happen when your property is assessed at a higher percentage of market value than your neighbors. Washington law requires uniformity: all properties in the same class should be assessed at roughly the same ratio to market. Say similar homes on your street sold for $750,000 and are assessed at $730,000 (about 97 percent), but your home is assessed at $820,000. That's a uniformity argument even if $820,000 might be defensible on its own.
What is the appeal deadline for King County property tax assessments?
This is the one number you can't afford to blow. Under RCW 84.48.010, you file your appeal with the King County Board of Equalization (BOE) by August 1 of the assessment year, or within 60 days of the mailing date on your value notice, whichever is later. [4]
Most Annual Value Notices go out in the spring, so August 1 is the real deadline for the majority of King County homeowners. Miss it and you generally can't appeal that year's value at all. You can appeal again the following year, but you've lost this round.
One circumstance buys you more time. If the assessor corrects or changes your value after the first notice (after a physical inspection or a data fix, for example), you get 60 days from that corrected notice.
File early. The BOE takes in thousands of petitions each summer. Filing two weeks ahead gives you room to fix any paperwork problem they flag. Filing the morning of August 1 does not.
Here's the working calendar:
| Event | Typical Timing |
|---|---|
| Assessment date (valuation as-of date) | January 1 |
| Annual Value Notices mailed | March to June |
| Appeal filing deadline | August 1 (or 60 days from notice) |
| BOE hearings begin | Late summer through the following year |
| Tax bills mailed (first half due) | April 30 |
| Tax bills (second half due) | October 31 |
How do you file a King County property tax appeal yourself?
Filing your own appeal is not complicated. Here's the actual process, step by step.
First, get your Annual Value Notice. It has your parcel number, the assessed value being challenged, and the deadline. Keep the envelope it came in, because the postmark can matter if anyone disputes when the notice was mailed.
Second, pull your property record from the King County Assessor's website (kingcounty.gov/assessor). Look up your parcel and download the residential property detail report. Check every field: bedrooms, bathrooms, total living area, year built, condition grade, and the comparable sales the assessor used. Write down anything wrong or anything you'd dispute.
Third, download the appeal petition form from the King County Board of Equalization. The BOE is a separate agency from the Assessor. [5] The petition asks for your name, parcel number, current assessed value, and your opinion of value. You don't need a precise opinion of value at filing, but have a good-faith number in mind.
Fourth, gather your evidence before the hearing. Three kinds of evidence win cases: comparable sales, your own recent purchase price if you bought in the last year or two, and a private appraisal. Comparable sales are the workhorse of a DIY appeal. Pull sales from the six months before January 1 of the assessment year using the King County Parcel Viewer or Zillow, filter for homes within a half-mile with similar square footage, lot size, condition, and age, then build a simple comparison table showing each sale price and adjusted value. If four comparable homes averaged $720,000 and yours is assessed at $850,000, that gap is your case.
Fifth, submit the petition by the deadline. The BOE takes petitions by mail, in person, or online. Keep a copy and get confirmation of receipt.
Sixth, prepare for the hearing. Most BOE hearings are informal, under 30 minutes, run over Zoom or phone. You present your evidence, the assessor's appraiser responds, the board asks questions. No lawyer needed. Organized, printed evidence beats legal argument every time. Show up on time, be brief, let the numbers talk.
Want a structured framework for finding comps and organizing your presentation? TaxFightBack's DIY appeal kit walks through exactly that, so you keep 100 percent of any savings instead of handing a cut to a contingency firm.
What evidence actually wins a King County Board of Equalization appeal?
The BOE starts from the position that the assessor's value is presumed correct. The burden is on you to prove your opinion of value is more accurate. That sounds steep, but in practice any credible, organized evidence shifts the whole conversation.
Comparable sales ("comps") are the backbone of most wins. A good comp sold within 12 months of January 1 of the assessment year, sits within a half-mile or in the same neighborhood, matches your size within about 200 square feet of living area, is close in age and condition, and is an arm's-length sale between unrelated parties. Foreclosures, estate sales, and sales between relatives usually get thrown out. Bring at least three comps. Five or six is better.
Data error corrections are fast wins. If the assessor lists your home at 2,200 square feet but the building permit shows 1,950, bring the permit and a floor plan. The appraiser at your hearing will often concede a correction on the spot when you show documentation.
A private appraisal is the single strongest piece of evidence, but it runs $400 to $700 for a residential appraisal in King County, and it's only worth it if the potential savings justify the cost. On a $50,000 over-assessment at a $10 per $1,000 rate, you save $500 a year. A $600 appraisal pays for itself in year two if you win. On a smaller gap, skip it and use comps.
Condition photos matter more than people expect. Dated shots of a failing roof, water damage, a cracked foundation, or an unfinished basement can support a real downward adjustment to the assessor's condition grade, which can swing assessed value 10 to 20 percent on older homes.
What doesn't help: emotional pleas ("I can't afford this bill"), comparisons to taxes in other states, or arguments about the levy rate. The BOE has authority over assessed value only, not rates or levy amounts.
What exemptions can reduce your King County property tax bill?
Washington offers a Senior Citizen and Disabled Persons exemption that freezes the assessed value for qualifying homeowners and cuts the levy rate. [6] Income limits apply and get updated each year. For 2024 taxes, the most generous tier applied at $40,000 or less, with partial relief available up to $58,423. [6] You have to be 61 or older by December 31 of the application year, or retired because of disability at any age.
This one is genuinely big. Qualifying homeowners save thousands a year. If you or a co-owner qualifies, apply now at the King County Assessor's office. The deadline is usually December 31 of the year before you want the benefit.
The Current Use program (open space, farm, and timberland) values qualifying agricultural or undeveloped land at its current use rather than its highest-and-best use. [7] That helps owners of larger parcels in the rural and semi-rural parts of King County.
Active-duty military members may qualify for a property tax exemption during deployment under RCW 84.36.379. [8]
None of these exemptions cost you the right to appeal the assessed value separately. You can apply for an exemption and appeal the base value at the same time.
What happens after the King County Board of Equalization decides?
The BOE mails a written decision after your hearing, usually within a few weeks. It states the new (or unchanged) assessed value.
Lose at the BOE, or get a smaller reduction than you hoped? You can appeal further to the Washington State Board of Tax Appeals (BTA). [9] The BTA hears cases de novo, meaning fresh. You present your evidence again and the board acts independently. The residential filing fee is $100 (confirm current fees at bta.wa.gov). The BTA is more formal than the BOE but still workable without an attorney.
Beyond the BTA, appeals go to Superior Court. That step realistically needs a lawyer and mostly comes up in commercial disputes where the stakes justify litigation.
If the BOE or BTA cuts your value after you've already paid taxes on the higher number, King County issues a refund. Prior-year overpayments show up as a credit on your next statement or as a check, depending on what you request.
One thing to keep in mind. A BOE reduction applies to that assessment year only. It does not carry forward on its own. If the assessor raises your value again next year, you appeal again. King County reassesses the neighborhood on its normal cycle regardless of last year's outcome.
How does King County compare to other large county assessment systems?
Washington is a full-value assessment state, so the legal standard is 100 percent of market value. That's stricter than fractional-assessment states. Illinois, for one, assesses at a fraction of market value (the Cook County residential level is 10 percent of market as a matter of classification), which adds a conversion step that trips up a lot of homeowners. See our guide to the cook county tax assessor tax bill for how that system works.
California caps assessed value increases at 2 percent a year under Proposition 13 unless the property sells, so longtime owners pay far below market value. See los angeles county property tax for how that plays out. Washington has no such cap, so King County values can spike hard in a hot market and your bill spikes with them.
Arizona's Maricopa County runs a limited value system with a cap on annual increases for tax purposes, kept separate from full cash value. The maricopa property tax guide covers that split. Texas counties, including Bexar County, assess at market value but hold taxable value increases to a 10 percent homestead cap, which Washington doesn't have.
On win rates, be skeptical of clean numbers. The Washington Department of Revenue doesn't publish residential BOE success rates in a tidy statewide table, and county-level win-rate data isn't available in a form I'd trust. The King County BOE's own annual reports show that a meaningful share of residential appeals end in at least a partial reduction, which lines up with the general pattern: appealing with solid comps is worth the effort.
Other high-value metro counties with active appeal cultures include San Diego and Lake County, Illinois. The mechanics differ, but the core logic holds everywhere: find comps below your assessed value and present them.
What are the most common mistakes homeowners make in King County appeals?
Missing the deadline is number one by a wide margin. August 1 is hard. There's no informal grace period at the BOE.
Using listing prices instead of closed sale prices is second. The BOE cares what homes actually sold for, not what sellers hoped to get. Filter your comps to closed sales.
Picking comps that aren't really comparable is third. A 1,400-square-foot home from 1955 is not a comp for your 2,200-square-foot home from 1992, even on the same street. The assessor's appraiser will say so, and the board will discount your whole presentation.
Skipping the hearing is fourth. File and then no-show, and the BOE almost always rules for the assessor by default.
Failing to adjust for differences between your comps and your home is fifth. If your best comp sold for $710,000 but has a renovated kitchen yours lacks, show a downward adjustment from $710,000 to account for it. A clean table with simple adjustments (plus or minus for square footage, condition, lot size, garage) beats a raw list of sale prices.
Confusing assessed value with taxable value in exemption cases is sixth. If you have a senior exemption, part of your assessed value may be frozen or excluded. Your tax bill already accounts for that. Your BOE petition should be based on the assessed value shown on your Annual Value Notice, before any exemption adjustment.
Where can you find King County property records and comparable sales data?
The King County Assessor's website (kingcounty.gov/assessor) is your starting point. [2] The parcel search tool lets you look up any address and see the assessor's data for that property: sales history, lot size, building details, condition grade, and the assessed value for the current and prior years. It's free and public.
The King County Parcel Viewer is a map-based tool sitting on the same database. Click nearby properties to see their assessed values and recent sales, which makes building a comp set faster.
For closed sale prices, the assessor's database shows recorded prices on most arm's-length transactions. Washington is a deed-recording state, and sale prices get disclosed on the Real Estate Excise Tax Affidavit, which becomes public record. [10] So unlike some states, you can see exact sale prices for nearly every transaction in King County without paying for a subscription database.
Zillow and Redfin pull from the same NWMLS and public records data and are fine for a quick cross-check. For the formal hearing, though, the King County Assessor's own sales records carry more weight than a Zillow printout.
If you think a data error is driving your value, pull your property's permit history from the King County Permits portal (kingcounty.gov/permits). Permits show what work was done, when, and to what spec. They help both for confirming errors in the assessor's records and for supporting condition arguments.
Frequently asked questions
How do I appeal my King County property tax assessment?
File a petition with the King County Board of Equalization (BOE) by August 1 of the assessment year, or within 60 days of your value notice mailing date, whichever is later. Download the petition form from the BOE, fill in your parcel number and opinion of value, and submit it with supporting evidence. The BOE schedules a hearing where you present comparable sales or other proof that your assessed value tops market value.
What is the King County property tax appeal deadline?
August 1 of the assessment year, or 60 days from the mailing date of your Annual Value Notice, whichever is later. This deadline comes from RCW 84.48.010. If the assessor issues a corrected value notice later in the year, you get 60 days from that corrected notice. Miss the deadline and you generally can't appeal that year's value.
What is the King County property tax rate?
There's no single rate for the whole county. Each property's rate combines state, county, city, school, fire, and other levies for its specific taxing district. For 2024, rates ran roughly $8 to $12 per $1,000 of assessed value depending on location. Your exact combined levy rate is printed on your annual tax statement, available through the King County Treasury Operations website.
Is King County assessed value the same as market value?
By law it should be. Washington (RCW 84.40.030) requires county assessors to value property at 100 percent of true and fair value, which means current market value. In practice the assessor uses mass appraisal models and periodic inspections, so individual properties can drift from actual market value. That gap is the basis for an appeal.
How often does King County reassess property?
King County uses a four-year physical inspection cycle, so an appraiser actually visits each property roughly every four years. In off years, values get updated statistically using sales ratio analysis. Assessments are annual, though: you receive a new Annual Value Notice every spring, and each year's value can be appealed separately.
What happens at a King County Board of Equalization hearing?
Hearings are informal and usually run 20 to 30 minutes, mostly by Zoom or phone. You present your evidence (comparable sales, data corrections, photos, or an appraisal). An appraiser from the King County Assessor's office responds. The three-member BOE panel asks questions and deliberates. You get a written decision by mail within a few weeks of the hearing.
Do I need a lawyer or an agent to appeal my King County property taxes?
No. The BOE process is built for homeowners without legal representation. Most successful residential appeals are filed by owners who gathered comparable sales and organized their own evidence. Contingency firms take a cut of your savings, typically 25 to 50 percent. Filing yourself keeps all of it.
What is the King County senior exemption for property taxes?
Washington's Senior Citizen and Disabled Persons exemption freezes the assessed value used for state and local levies for qualifying homeowners. For 2024, income must generally be $58,423 or less, with larger reductions at or below $40,000. Applicants must be 61 or older by December 31 of the application year, or retired due to disability. Apply at the King County Assessor's office by December 31.
Can I appeal and apply for a senior exemption at the same time?
Yes. These are separate processes with separate offices and separate deadlines. Filing a BOE petition to lower your assessed value doesn't affect your exemption application, and an exemption doesn't waive your right to appeal the underlying assessed value. Doing both, if you qualify, gives you the biggest tax reduction.
If I lose my King County BOE appeal, can I appeal further?
Yes. You can appeal a BOE decision to the Washington State Board of Tax Appeals (BTA) at bta.wa.gov. The BTA hears the case fresh and is independent of both the county assessor and the BOE. The residential filing fee is $100 (confirm current fees on the BTA website). Beyond the BTA, appeals go to Superior Court, which realistically requires an attorney.
How do I find comparable sales for my King County appeal?
Start with the King County Assessor's parcel search at kingcounty.gov/assessor. Because Washington requires sale prices on the Real Estate Excise Tax Affidavit, actual closed prices are public record and visible in the assessor's database. Filter for sales within six months of January 1 of the assessment year, within a half-mile, with similar square footage, age, and condition. Aim for three to five comps.
Will a successful King County appeal reduce my taxes in future years?
Only for the year you appealed. The reduction applies to that assessment year's value. The assessor reassesses your neighborhood on its normal cycle and can raise your value again the following year. If the new value is again too high, file a fresh appeal. Some homeowners appeal every year when values keep rising faster than actual market conditions justify.
What if there's a data error in my King County property records?
Contact the King County Assessor's office directly to request a correction, before or after filing your BOE petition. If the error is clear (wrong bedroom count, wrong square footage), the assessor may fix it without a formal hearing. If the correction lowers your value, great. If the assessor disagrees, pursue the BOE appeal with your documentation, including permits, floor plans, or an appraisal sketch, as evidence.
How does a King County appeal differ from appeals in other large counties?
King County assesses at 100 percent of market value with no cap on annual increases, unlike Texas (10 percent homestead cap) or California (2 percent annual cap under Prop 13). The BOE hearing is administrative and informal, similar to most county appeal boards. The main difference from Cook County or Nassau County is that Washington's full-value standard makes comp-based arguments more direct, since there's no fractional assessment to convert.
Sources
- Washington State Legislature, RCW 84.40.030 (True and fair value defined): Washington State law requires property to be assessed at 100 percent of true and fair value
- King County Department of Assessments (kingcounty.gov/assessor): King County revalues each neighborhood on a four-year physical inspection cycle with statistical updates in off years; parcel records including condition, square footage, and sales are publicly searchable
- King County Assessor, Annual Report and levy rate summaries: Average combined levy rates in King County for 2024 varied by taxing district, generally ranging from approximately $9 to $11 per $1,000 of assessed value for residential properties
- Washington State Legislature, RCW 84.48.010 (Appeal deadline to Board of Equalization): Taxpayers must file appeals with the county Board of Equalization by August 1 or within 60 days of the mailing of the value notice, whichever is later
- King County Assessor, Senior Citizen and Disabled Persons Exemption Program: For 2024, the senior/disabled exemption income threshold is $58,423 or less; the most generous tier applies at $40,000 or less; applicants must be 61 or older by December 31 of the application year
- Washington State Department of Revenue, Property tax section: Washington's current use program values qualifying agricultural, open space, and timberland at current use value rather than highest-and-best-use market value
- Washington State Legislature, RCW 84.36.379 (Military exemption): Active-duty military personnel may qualify for a property tax exemption during deployment under RCW 84.36.379
- Washington State Board of Tax Appeals (bta.wa.gov): Homeowners who lose at the King County BOE can appeal further to the Washington State Board of Tax Appeals, which hears cases de novo; the residential filing fee is $100
- Washington State Legislature, RCW 84.40.020 (Annual assessment requirement): Washington law requires annual assessment of all taxable property; there is no statutory cap on year-over-year assessed value increases for most residential property