A Sammamish property assessment appeal starts with a single sheet of paper: the valuation notice King County mails once a year. Most owners glance at the number, compare it to what the house next door listed for, and file the notice away. A few think the number is wrong. For those owners, there is a defined process, a hard deadline, and a board that only listens to one kind of argument.

This guide walks through that process step by step, using the rules as the King County Board of Appeals and Equalization and the King County Assessor state them, the state law behind them, and the Assessor's own 2026 report on the Sammamish Plateau. Everything was checked at those sources in September 2026. We are real estate agents, not tax advisors or attorneys, so this is a description of the process, not advice on whether to file, and no one can promise an outcome.

How a Sammamish Property Assessment Appeal Works

Washington law sets the standard. RCW 84.40.030 says all property must be valued at 100 percent of its true and fair value, based on sales of the property or similar properties. RCW 84.40.020 says real property is assessed every year with reference to its value on January 1 of the year it is assessed. That date matters more than anything else in an appeal. The question is never what your home is worth today. It is what it was worth on January 1.

The timing trips people up. Per the Board of Appeals and Equalization, the assessment year is the year before the tax is due. A value set as of January 1, 2026, drives the property taxes you pay in 2027. The Assessor mails value notices between May and November of the assessment year, area by area, as each area's values are finished.

The Board also tells you up front what it cannot consider. Citing WAC 458-14-056(5), it says assessment comparisons of other properties, percentage of value increases, personal hardship, amount of tax, and other matters unrelated to market value cannot be considered. And by law, the Assessor is presumed to be correct, so the burden of proof is on the owner. A Sammamish property assessment appeal is, in plain terms, an argument that the house would not have sold for the assessed value on January 1.

For how the value turns into a tax bill, see our Q&A on what property taxes are like in Sammamish. The steps below are about the value itself.

Step 1: Find Your Deadline on the Notice

King County's deadline is July 1 of the assessment year or 60 calendar days after the mailing date printed on your value notice, whichever is later. That is the county's version of the state rule in RCW 84.40.038, which lets a county set a window of up to 60 days.

• Read the mailing date, not the date it arrived. Why it matters: the 60 days run from the date printed on the notice.
• Confirm the date in eAppeals. The Board's filing system shows your appeal due date when you look up your address or parcel number. Why it matters: it removes the guesswork.
• Wait for the notice before filing. The Assessor asks owners to file only after the current year's notice has arrived. Why it matters: a petition has to include a copy of that notice.
• If you missed it. RCW 84.40.038 lets the Board waive the deadline for good cause, such as a death or serious illness in the family, if the petition is filed within a reasonable time. Otherwise, the next notice is the next chance.

For the Plateau in 2026, the Assessor's report on the two Sammamish areas was accepted for the tax roll on June 3, 2026, so those notices went out after that date. Check the date on yours.

Step 2: Check Your Property Record Before You Appeal

Some wrong values are not a market disagreement at all. They are a data error. The Assessor's appeal page recommends reviewing your property characteristics in eReal Property first, and contacting the Assessor's office at 206-296-7300 or [email protected] if something is off. If the correction produces a value you agree with, you may not need to file at all.

This step is worth real attention on the Plateau. The Assessor's 2026 report says every property is physically inspected at least once in a six-year cycle, and that inspections are mostly exterior, with few interior inspections. So look at what the record says inside the house:

1. Finished square footage and basement finish. Why it matters: a daylight basement recorded as finished when it is not, or the reverse, moves the value.
2. Bedroom and bathroom counts. Why it matters: these feed the Assessor's model directly.
3. Building grade and condition. Why it matters: a 1990s home with original systems can be carried at a condition it no longer has.
4. View and waterfront flags, and lot size. Why it matters: the model adjusts for them, and on a hillside lot a recorded view can be generous.
5. Recent permits. Why it matters: a remodel adds value on the record. If you are weighing one, our Sammamish remodel ROI guide covers what projects tend to return.

Step 3: Decide Whether a Sammamish Property Assessment Appeal Is Worth Filing

The Assessor publishes a report for every residential area, and the 2026 report for Areas 35, 69 and 75 covers the North Sammamish Plateau (Area 35) and the South Sammamish Plateau (Area 69). Here is what it says about the values on this year's notices:

• The values went down on average. The average total value across all homes fell 4.4 percent in Area 35, from $1,656,700 to $1,583,100, and 4.5 percent in Area 69, from $1,676,000 to $1,601,400.
• They are built from three years of sales. The Assessor analyzed 958 sales in Area 35 and 922 in Area 69, from January 2023 through December 2025, with each price time-adjusted to January 1, 2026.
• They sit a little under the sales. After the revalue, the median ratio of assessed value to time-adjusted sale price was 0.918 in Area 35 and 0.922 in Area 69, inside the 0.90 to 1.10 range the International Association of Assessing Officers recommends.
• Land values were carried forward. The report's land update multiplies each previous land value by 1, so the change this year came through the improvement side of the model.

Two practical points follow. First, a notice that shows a lower value than last year is not proof the number is right; the question is still January 1 market value for your specific house. Second, because typical assessments in both areas landed around 92 percent of sale prices, an owner whose assessed value is somewhat below what they would list the home for today is looking at an ordinary result, not an error. The cases worth a closer look are ones where the assessed value is at or above what comparable homes actually sold for near January 1, or where something about the property, like a slope, an easement or a failing system, is not reflected in the record. Lakefront homes on the east shore are valued separately, in the Assessor's Area 47 Lake Sammamish report.

Step 4: Build the Evidence for Your Sammamish Property Assessment Appeal

The Board is clear that compelling market-based evidence is the key. Its list of evidence that works, and the Assessor's, comes down to these:

1. Comparable sales close to January 1. The Board says comparables do not have to match exactly, and that the examples that carry weight are sales in your neighborhood, with similar land and building features, that sold closest to the valuation date. Why it matters: a sale in June 2026 says less about January 1 than one in December 2025.
2. A sale of your own home. If you bought near the valuation date, the price you paid is evidence the Board lists by name. Why it matters: it is a direct measure of the market for that house.
3. Contractor estimates for defects. Written estimates to repair building or land problems. Why it matters: a roof at the end of its life or a failing retaining wall is a market fact that a mass-appraisal model does not see.
4. Development limits and sensitive areas. Letters from government agencies about development limitations, and proof that environmentally sensitive areas exist on the property. Why it matters: on the Plateau's steep edges, the City's buffers can shrink what a lot can hold. Our guide to trees, slopes and what you can build on a Sammamish lot explains where those rules come from.
5. Easements and access. Recorded deeds describing easements that affect value, and maps showing traffic or access limits.
6. An independent appraisal and photographs of conditions that reduce market value.

For help finding comparable sales, the Board points owners to the Assessor's website, the county's Property Tax Advisor's Office (206-477-1060, residential properties only), and real estate agents and title companies. For a broader picture of where Sammamish prices sit this year, see how much homes in Sammamish cost in 2026.

Step 5: File the Petition

You file one petition per parcel, online through eAppeals or by mail to the King County Board of Equalization, 516 Third Avenue, Room 1222, Seattle, WA 98104. The Board does not accept petitions by email and cannot consider an incomplete one. A complete petition includes:

• The parcel number, your name, address, signature and date
• Your representative, if any, with a power of attorney
• A description of the property: address, lot size, zoning and general building information
• The Assessor's value and your opinion of value
• Specific reasons, with evidence, why the Assessor's value does not reflect true and fair market value
• A copy of the value change notice

After filing, the Board sends an acknowledgment and forwards the petition to the Assessor for review. The Assessor's page notes that with a prompt submission that includes your evidence, you could receive a reduction offer without attending a hearing.

Step 6: The Hearing and What Comes After

If the petition goes to a hearing, the Assessor's page lays out the schedule. The Board notifies you of the date about 45 days in advance. Evidence from both sides is due 21 business days before the hearing. Each appeal gets 40 minutes, with both sides giving testimony and questioning the other's evidence. Decisions usually come within 45 days.

• Outcomes. The county says about 25 percent of appeals result in some type of reduction. That also means most do not.
• If the value comes down, the Treasurer either sends a revised tax statement or refunds what you have already paid.
• If you disagree with the decision, you or the Assessor can appeal to the Washington State Board of Tax Appeals within 30 days of the decision's mailing date.
• Keep paying. An appeal does not pause the tax bill. The county says to pay by the due date to avoid interest and penalties.

Assessed Value vs. Market Value When You Sell

Sellers ask about the assessed value for a different reason: buyers see it on listing portals and wonder why it differs from the list price. The honest answer is that the two numbers measure different things. The assessment is a mass-appraisal estimate of January 1 value, built from three years of time-adjusted sales and, in 2026, set around 92 percent of those sales on the Plateau. A list price reflects the house as it shows today, in today's market, with its updates and condition. A lower assessed value is not a signal that a home is overpriced, and a successful appeal does not lower what a buyer will pay. When you get to that stage, our breakdown of what it costs to sell a home in Sammamish covers the other numbers that matter.

Owners weighing whether to stay or move, and whether county senior tax relief applies, will find that decision laid out in aging in place or moving: a Sammamish homeowner's decision. For the full carrying cost of a Plateau home, see how much it costs to live in Sammamish.

This article describes King County's public appeal process and is not tax or legal advice. Rules, deadlines and procedures are set by state law and the county and can change. For help with a petition, contact the King County Property Tax Advisor's Office or a qualified professional.

Frequently Asked Questions About a Sammamish Property Assessment Appeal