Bay Area Property Tax Appeal 2026: County-by-County Guide

Your 2026 property tax assessment notice is arriving this month, and if the county's value looks too high, you have a limited window to challenge it. The deadline and the cost to file both depend on which county you live in, and the spread is wider than most people expect.

The key dates first. In Santa Clara and Alameda counties, the deadline to file a formal property tax appeal is September 15, 2026. In San Mateo, Contra Costa, and Marin, you have until November 30, 2026. Miss your county's date and you wait a full year for the next chance.

This guide covers what your assessment notice actually means, how an appeal works in each of the five counties, what it costs, and how to decide whether filing is worth it.

What your assessment notice means

The number on your notice is your assessed value, which is what your property tax is calculated on. It is not the same as your market value, and a rising countywide assessment roll does not mean your own assessment is unfair.

Two rules set your assessed value. Under Proposition 13, your assessment can rise no more than 2 percent a year for as long as you own the home, regardless of how fast the market moves. And the assessor values your property as of January 1, 2026, which is called the lien date. An appeal only helps if the assessor's value is higher than what your property was actually worth on that date.

This is why most long-time owners have nothing to appeal. If you have owned for several years, Prop 13 has almost certainly kept your assessed value well below market, so there is no gap to challenge. An appeal is worth pursuing only when your assessed value is above your property's real market value.

The two ways to challenge your value

There are two separate processes, and confusing them is how people miss the deadline.

The first is an informal decline-in-value review, also called a Prop 8 request. You ask the assessor's office directly to lower your value and provide comparable sales to support it. It is free, there is no hearing, and it is the fastest route when your case is clear. The limitation is that the decision is up to the assessor, and it does not preserve your right to a formal hearing if they say no.

The second is a formal assessment appeal, an application filed with your county's Assessment Appeals Board. This is the filing that carries the legal deadline and, in most counties, a fee. It gives you the right to present your case to the board.

Practical advice: if your value is clearly too high, file the formal appeal before your county's deadline even if you also try the informal route. You can withdraw the formal appeal later if the informal review succeeds. If you skip it and the informal review fails, you have lost your window for the year.

Deadlines and fees by county

California counties fall into two deadline groups. Counties that mail a value notice to every property owner use a September 15 deadline. The rest use November 30. Among these five, Santa Clara and Alameda are September 15 counties. San Mateo, Contra Costa, and Marin give you until November 30.

The filing fees vary widely, and Santa Clara's is brand new for 2026.

*Alameda's most recent certified roll. Its 2026 figure is still being finalized, but the September 15 deadline and the $50 fee apply now.

Santa Clara's new appeal fee

Santa Clara County used to charge nothing to file an appeal. That changed this year. In February 2026, the Board of Supervisors approved a nonrefundable filing fee effective June 1: $290 per parcel for a home and $675 for commercial or larger multifamily property. County Executive James Williams said the appeals system costs the county about $3.5 million a year to run, and the fees are expected to recover roughly $3.4 million of that.

For comparison, Los Angeles County charges $50 to file and San Francisco charges $120, so Santa Clara is now among the most expensive counties in the state. If you own there, this matters for one reason: a nonrefundable $290 fee can exceed the tax savings on a small overassessment. Estimate your likely savings before you file. In the other four counties, at $30 to $50, the fee rarely changes the decision.

When a property tax appeal is worth filing

Filing makes sense in a few specific situations.

You bought recently and near the top of the market. If you closed in 2021 or 2022, or paid over asking in a competitive stretch, and comparable sales around January 1, 2026 came in lower, your assessed value may be too high.

You own commercial or office property. This is where most Bay Area appeals are happening right now. In Santa Clara alone, about $153.6 billion in assessed value is under appeal, with office vacancy near 20 percent.

Your assessed value is above market. If the county's number is higher than what your home would sell for on the lien date, you have grounds. This also covers plain record errors, such as wrong square footage or lot size.

When it is not worth it

You have owned for years. Prop 13 has likely kept your assessed value below market, so there is no gap to appeal, no matter how large the countywide roll gets.

The likely savings is small and you are in Santa Clara. A $290 nonrefundable fee can erase the benefit of a minor reduction.

One thing to know in every county: an appeal does not lower your current bill while it is pending. Keep paying your installments on time or you will owe penalties. If you win, the county refunds the overpayment.

How to build your case

Your goal is to show that your property was worth less on January 1, 2026 than the assessor says. The strongest evidence is comparable sales: three to five homes similar to yours in size and condition, in your neighborhood, that sold close to that date. Use lien-date sale prices, not today's asking prices.

Local detail is what wins these. A countywide average tells you nothing about your specific area, and the appeals board only cares about your property and its immediate surroundings. Before you decide, look at what your neighborhood actually did rather than the county as a whole. Houseberry's neighborhood rankings for Silicon Valley, the Peninsula, the East Bay, and Marin are a useful starting point for comparing how areas within your county are holding up on price and value.

Common questions

Does an appeal lower my tax bill right away?

No. Keep paying your installments by the due dates while the appeal is pending, or you will rack up penalties. If you win, the county issues a refund.

Can I appeal if I just bought the house?

You can file, but a recent purchase price is strong evidence of market value, so your grounds are usually weak unless the market dropped after you bought.

What if I miss my county's deadline?

You wait for next year's roll to file a formal appeal, or ask the assessor for an informal decline-in-value review, which has no fixed statutory deadline but does not give you hearing rights.

Do I need to hire someone to appeal?

For a typical home, no. You can file the application and present comparable sales yourself. Tax agents and attorneys are most useful for commercial property or complicated cases, and many charge a share of the savings.

Bottom line

If you own in Santa Clara or Alameda, your deadline is September 15, 2026, and Santa Clara owners should weigh the new $290 fee before filing. If you own in San Mateo, Contra Costa, or Marin, your deadline is November 30, 2026. Compare the number on your notice against what your home would actually sell for. If it is too high, file before your deadline. If it is fair, there is nothing to do.

Sources

• San Mateo County 2026 assessment roll, The Almanac
• Santa Clara County record 2026 roll, The Real Deal
• Contra Costa County 2026-2027 assessment roll news release
• Marin County 2026 assessment roll grows 3.62%
• Santa Clara County new assessment appeal fees, Mountain View Voice
• Santa Clara County assessment appeal dates and deadlines
• Alameda County assessor calendar and important dates
• San Mateo County appeal an assessment
• Contra Costa County assessment appeals
• Marin County appeal your property tax assessment