King County property tax is calculated by multiplying your home’s assessed value by the combined levy rate for your taxing district, then billed in two installments due April 30 and October 31 each year. The King County Assessor sets the value; the King County Treasurer collects the money. Missing a deadline triggers monthly interest plus flat penalties, so the first thing most owners need to know is the number on their statement and the date it is due.
How the Bill Is Calculated
Two numbers drive your bill: assessed value and levy rate. Washington law requires the Assessor to value real property at 100 percent of fair market value as of January 1 each year.1Washington State Legislature. RCW 84.40.030 – Manner of Assessment Fair market value is what a willing buyer would pay a willing seller in an open transaction, and the Assessor updates the figure annually to reflect recent sales and any physical changes.
The levy rate is expressed as dollars per $1,000 of assessed value and combines the state school levy, your city, fire and library districts, and any voter-approved measures. Washington caps regular levies at one percent of true and fair value, which works out to $10 per $1,000.2Washington State Legislature. RCW 84.52.050 Voter-approved lid lifts and excess levies sit on top of that cap, which is why actual combined rates in many King County areas run well above $10 per thousand.3King County, Washington. City Tax Comparison for 2025-2026
To estimate your bill, divide assessed value by 1,000 and multiply by the levy rate. A home assessed at $600,000 in an area with a $13 per thousand rate would owe $7,800 for the year.
Due Dates and What Late Payment Costs
The annual bill splits in two. The first half is due on or before April 30, and the second half is due on or before October 31. If your total annual bill is $50 or less, the entire amount is due by April 30.4Washington State Legislature. RCW 84.56.020 – Taxes Collected by Treasurer
Interest accrues at one percent per month from the delinquency date, which comes to 12 percent annually.4Washington State Legislature. RCW 84.56.020 – Taxes Collected by Treasurer Two flat penalties stack on top of that interest during the same year the tax is due:
- A three percent penalty is added on June 1 to any first-half amount still unpaid.
- An eight percent penalty is added on December 1 to any remaining balance from that year.
Penalties are calculated on the unpaid tax, not on the accruing interest. A homeowner who ignores a $5,000 first-half bill through year-end would owe the original $5,000 plus months of interest plus $150 in June and $400 in December. Unpaid taxes eventually become a lien on the property.
How to Pay
Every parcel has a tax account number that identifies it in the Treasurer’s system. It appears on your mailed statement and can be looked up by address through King County’s eReal Property tool.5King County, Washington. Property Research Having the correct number before you pay prevents misapplied payments.
The county accepts payment four ways:6King County, Washington. Property Taxes
- Online, through the county’s eCommerce portal. Credit and debit cards carry a 2.35 percent processing fee; electronic checks cost a flat $0.55.7King County. King County Property Tax Bulletin
- By mail, with a check, cashier’s check, or money order sent to King County Treasury, 201 S. Jackson St., Suite 710, Seattle, WA 98104. Write your tax account number on the check, and make sure the envelope is postmarked by the due date.
- In person, at the King County Customer Service Center, 201 S. Jackson St., second floor, Monday through Friday, 8:30 a.m. to 4:30 p.m. Checks, money orders, cards, and cash are accepted.
- Drop box, at Second Avenue and South Jackson Street, during business hours. Checks and money orders only; no cash.
If Your Mortgage Lender Pays for You
If you have a mortgage, your lender may collect property tax as part of your monthly payment and hold the money in escrow until the installments come due. FHA-insured loans require escrow for taxes and insurance.8U.S. Department of Housing and Urban Development. Chapter 2 – HUD Escrow and Mortgage Insurance Conventional loans with less than 20 percent equity typically require it too.
Federal rules under RESPA cap the cushion your servicer can hold at roughly two months of payments, and the servicer must perform an annual escrow analysis and refund any surplus.9eCFR. 12 CFR 1024.17 – Escrow Accounts When King County assessments jump, your monthly mortgage payment usually rises at the next escrow adjustment. A shortfall can be spread over up to 12 months or collected in a lump sum.
Exemptions for Seniors, People With Disabilities, and Veterans
Washington’s property tax exemption program can substantially cut what eligible homeowners owe on their primary residence. State law sets the structure, and income thresholds track the median household income in each county.10Washington State Legislature. RCW 84.36.381 – Exemptions – Residences – Requirements
You qualify if you meet one of these:
- At least 61 years old by December 31 of the filing year.
- Retired from regular employment due to a disability.
- A veteran with a VA service-connected disability compensation rating of 80 percent or higher, or a total disability rating for a service-connected condition.
In King County, the combined household disposable income limit for taxes collected in 2024 through 2026 is $84,000.11King County, Washington. Senior Citizen and People with Disabilities Exemption Program Instructions The amount of relief depends on which of three income tiers you fall into:
- Threshold 1, the lowest income tier: regular taxes are exempt on $60,000 or 60 percent of assessed value, whichever is greater, plus full exemption from excess levies and Part 2 of the state school levy.
- Threshold 2: regular taxes are exempt on $50,000 or 35 percent of assessed value, whichever is greater, capped at $70,000, plus full exemption from excess levies and Part 2 of the state school levy.
- Threshold 3, up to $84,000: exemption from excess levies and Part 2 of the state school levy only.
The dollar cutoffs separating the tiers are recalculated every three years based on King County’s median household income.12Washington State Legislature. RCW 84.36.383 You apply through the King County Assessor’s office with proof of age or disability, proof of residency, and income documentation.
The Deferral Program
If you qualify for the exemption but still can’t cover the remaining balance, you can defer the tax instead. Washington’s deferral program has the state pay the tax on your behalf and record a lien on your home. The deferred amount accrues interest at five percent per year, and the lien can grow to a maximum of 80 percent of your equity in the property.13FindLaw. Washington Revised Code Title 84 Property Taxes 84.38.100
The balance comes due when you sell, move out, or pass away. If you have a mortgage, your lender typically must cosign the deferral declaration, because the state’s lien is subordinate to the mortgage but senior to most other claims. Deferral can work for a homeowner on a fixed income who plans to stay put, though the compounding five percent interest means the eventual payoff grows substantially over a decade or more.
Appealing Your Assessed Value
If you think the Assessor overvalued your property, you can appeal to the King County Board of Equalization, an independent panel that reviews valuation disputes. The petition must be postmarked, hand-delivered, or filed online by the later of July 1 of the assessment year or 60 days from the mailing date on your value change notice.14King County, Washington. How to Appeal a Property Tax Assessment Miss that window and you lose the right to challenge until the next cycle.
An appeal must focus on fair market value, not on the tax bill itself. The Board decides whether the assessed value exceeds what the property would actually sell for.15Washington State Legislature. RCW 84.48.010 The strongest evidence is recent sale prices of comparable homes in your area close to the January 1 assessment date, documentation of structural problems or deferred maintenance that reduce value, and a licensed appraiser’s report (particularly for unique or high-value properties).
The Board must notify you and the Assessor of its decision within 45 days of the hearing.15Washington State Legislature. RCW 84.48.010 If you disagree with that ruling, you can escalate to the Washington State Board of Tax Appeals.
Deducting the Tax on Your Federal Return
King County property tax is deductible on your federal return if you itemize, but a cap limits the write-off. Under 26 U.S.C. ยง 164, the total deduction for state and local taxes (property, income, and sales combined) cannot exceed $40,400 for the 2026 tax year, or $20,200 for married filing separately.16Office of the Law Revision Counsel. 26 USC 164 – Taxes The cap increases by one percent annually through 2029, then drops to $10,000 in 2030.
Only the actual property tax qualifies. Service charges like trash collection or water and sewer fees are not deductible, nor are special assessments for local improvements such as sidewalks or street paving that add value to your property.17Internal Revenue Service. Publication 530 – Tax Information for Homeowners HOA dues and transfer taxes are also excluded. Because Washington has no state income tax, many King County homeowners find the property tax alone consumes most or all of the available SALT deduction.