Washington splits its property tax bill into two halves: the first was due April 30, and the second is due October 31. In 2026, October 31 lands on a Saturday — and when the deadline falls on a weekend or county holiday, Washington treasurers generally move it to the next business day. King County did exactly that the last time this happened, in 2021, when the deadline became Monday, November 1. This year, expect Monday, November 2, 2026.
That said, don't plan around the extra two days unless you've confirmed it with your county. Paying online by Friday, October 30 removes the question entirely.
Who Actually Owes This Payment
If you paid your full-year bill back in April, you're done. If your mortgage has an escrow account, your lender pays this installment for you — but it's worth logging into your county treasurer's site in early November to confirm the payment posted. Everyone else who paid only the first half in April owes the second half now.
One quirk: if your total annual tax was $50 or less, the whole amount was due in April. There's no second half to pay.
What Happens If You Miss It
Washington changed its delinquency rules in 2021 (Engrossed Substitute House Bill 1410), and the change works in homeowners' favor. For residential property with four or fewer units — including manufactured and mobile homes — there's no penalty on late payments anymore. Instead, unpaid tax accrues interest at 9% per year until it's paid. Other property types are charged a higher interest rate.
Nine percent a year isn't catastrophic for a few weeks' delay, but it isn't nothing either, and it compounds the risk if the balance sits. Unpaid Washington property taxes eventually lead to foreclosure after three years of delinquency.
Paying by Mail
If you mail a check, the postmark matters, not the day the treasurer opens the envelope. Washington law also gives some leeway for mail that arrives with no readable postmark: if it's received within three business days of the deadline, it's treated as on time. Still, a postmark you can prove beats a rule you're hoping applies — if you're cutting it close, pay online or in person.
Check Your County
Every Washington county sets its own payment portal, fees for card payments, and office hours. Find your county's treasurer and exact deadline on our Washington property tax page, or go straight to a big one like King County.