When Silicon Valley prices soften, the question I hear most from homeowners isn’t about selling at all. It’s “if my house is worth less now, shouldn’t my property tax bill go down too?” Sometimes the answer is yes, and California has a specific rule for it called Proposition 8, or “decline in value.” After more than 23 years and 460-plus transactions in Santa Clara and Santa Cruz counties, I can tell you it’s one of the most misunderstood parts of our property tax system. Here’s how it works, who it really helps, the deadlines that matter, and how to ask for a review without paying anyone a dime.
Key Takeaways
Summary: If your Silicon Valley home’s market value on January 1 falls below its Prop 13 factored base year value, Proposition 8 lets you ask the County Assessor for a free, temporary reduction, which mostly helps people who bought or were reassessed near recent price peaks.
What Proposition 8 Actually Does
To understand Prop 8, you have to start with its older sibling. According to the California State Board of Equalization (BOE), Proposition 13 passed in June 1978 and set most property assessments at their 1975 values, capped the base tax rate at 1% plus voter-approved bonds, and limited annual assessment increases to 2%. Five months later, in November 1978, voters passed Proposition 8, which allows a temporary reduction when a property’s value falls. It lives today in Revenue and Taxation Code section 51.
Here are the three terms that make the whole thing click. Your base year value is the market value when you bought the home (or when it was last reassessed because of new construction or a change in ownership). Your factored base year value is that number bumped up each year by the lower of California’s inflation rate or 2%. For the 2026-27 tax year, the BOE told assessors to use the full 2% factor because California’s CPI rose 3.3%, per its annual inflation factor letter. A decline in value happens when your home’s market value on January 1, the lien date, comes in below that factored base year value.
When that happens, the Assessor is required to put the lower number on the tax roll. That’s really the whole rule. It’s not a discount or a special program you have to qualify for, it’s just the law making sure you aren’t taxed on more than your home is worth.
Who Actually Benefits From a Prop 8 Reduction (and Who Doesn’t)
This is the part that surprises people. If you’ve owned your home for 15, 25, or 40 years, your factored base year value is almost certainly a fraction of what the house is worth today, because it’s only been allowed to grow 2% a year while Silicon Valley values grew far faster. A 4% dip in the market doesn’t come close to closing that gap, so your bill won’t change. The good news is that the dip doesn’t hurt you either. Your base year value stays exactly where it is, and your taxes keep rising no more than 2% a year.
The people who are most likely to benefit look like this:
- Recent buyers, especially anyone who bought near the spring 2022 peak or during another hot stretch, whose purchase price became their base year value.
- Heirs whose inherited home was reassessed under Prop 19. When a child inherits a parent’s home and doesn’t qualify for the parent-child exclusion, the home is reassessed to market value as of the date of death. If that date fell near a peak, a later decline can push market value below the new base. My guide to Prop 19 for seniors walks through when that reassessment happens, and the BOE-502-D change in ownership statement is how it gets reported in Santa Clara County.
- Owners who added new construction like a big remodel or an ADU during a high-cost period, since new construction gets its own base year value at market. (Accessibility work is a different story, and many accessibility improvements are excluded from reassessment altogether.)
A Quick Example
Say you bought a home in Sunnyvale in spring 2022 for $2,000,000. That became your base year value. With four annual 2% inflation bumps on the January 1 lien dates from 2023 through 2026, your factored base year value for the 2026-27 roll is about $2,164,864. If comparable homes show your house was worth $2,050,000 on January 1, 2026, the Assessor should enroll $2,050,000 instead. That’s a $114,864 lower assessment, and at a tax rate of roughly 1.2%, about $1,380 off your bill for the year. Your actual rate depends on your tax rate area and local bonds, and it’s printed right on your bill.
Now flip it around. Say your parents bought that same house in 1990. Their factored base year value might be well under $700,000. The market could fall by half and they still wouldn’t qualify, which is exactly why Prop 8 headlines rarely apply to longtime owners.
Timing Is Everything: The January 1 Lien Date
Every Prop 8 review looks at one moment in time, your home’s market value on January 1. The BOE’s how-it-works page says the best evidence is comparable sales that closed close to January 1, and no later than March 31.
That has a big practical consequence right now. A price dip we’re seeing in fall 2026 won’t show up on this year’s bill at all. It gets measured on January 1, 2027, which drives the 2027-28 tax bill you’ll get in fall 2027, and you’d request the review in summer 2027 after the value notices go out. If you think you’ll qualify, start keeping an eye on sales of homes like yours from late 2026 through March 2027.
A few more timing rules worth knowing, straight from the BOE’s Prop 8 FAQ. Only the most recent January 1 assessment can be reviewed, so there’s no going back to fix last year. Prop 8 doesn’t apply to supplemental assessments, which are the extra bills new buyers get after a purchase. And you can’t hold off on paying while you wait. The first installment is due November 1 and becomes delinquent after December 10, and if your value gets reduced, the county sends a corrected bill or a refund.
How to Request a Decline-in-Value Review
Most county Assessors will do an informal review if you ask, and it costs nothing. The general process looks like this:
- Check your notice. Look at the assessed value on your annual value notice or tax bill. That’s the number you’re comparing against.
- Gather evidence. Pull three to five sales of homes similar to yours in size, condition, and location that closed as close to January 1 as possible, and no later than March 31. A recent appraisal can help too.
- Submit the request. Use your county’s informal review form or online request, and send it before the Assessor’s deadline.
- Wait for the determination. An appraiser compares your January 1 market value with your factored base year value and enrolls the lower one. You’ll get a notice or a corrected bill.
- Appeal if needed. If you disagree, or the Assessor hasn’t finished by the appeal deadline, file a formal assessment appeal with the county Clerk of the Board to protect your rights.
Santa Clara County
Owners get their assessed value notices by the end of June. The Santa Clara County Assessor’s Prop 8 page handles informal requests, and for the 2026-27 roll it listed August 8, 2026 as the cutoff for a request to be considered. If you need to go further, formal appeals are filed with the Clerk of the Board’s Assessment Appeals Division at 70 West Hedding Street in San Jose (408-299-5088) during the regular filing period of July 2 through September 15.
Santa Cruz County
The Santa Cruz County Assessor accepts decline-in-value applications every year from July 2 through December 31, with separate forms for residential, multi-family, and commercial property. You can turn it in by mail, email, or in person at 701 Ocean Street, and the office’s Real Property line is 831-454-2270. Santa Cruz County’s formal appeal window runs through November 30 (it moved to December 1 in 2025 because the 30th fell on a Sunday). If you own in Santa Cruz County and think your January 1, 2026 value was too high, you still have time this year, but don’t wait.
Other Bay Area Counties
Appeal deadlines differ by county. According to the BOE’s list of county filing periods, Alameda uses September 15 like Santa Clara, while San Mateo and Monterey use November 30. You can find every county’s Assessor and Clerk of the Board on the BOE’s county contacts page.
What Happens After Your Value Is Reduced
A Prop 8 reduction is temporary, and this is where people get caught off guard. The Assessor reviews properties in decline-in-value status every year. While you’re in that status, the 2% cap doesn’t apply, so as the market recovers your assessed value can jump 5%, 10%, or more in a single year. It can never go higher than your factored base year value, though, unless you sell or add new construction.
In other words, Prop 8 gives you a break in the soft years and then lets your assessment catch back up to where Prop 13 would have had it all along. You don’t lose anything in the long run, but don’t budget as if the lower bill is permanent. If you do get a big jump later and want to understand why, the BOE’s Taxpayers’ Rights Advocate is a good, free resource.
Don’t Pay a Company to File for You
When values dip, mailers start showing up offering to “lower your property taxes” for a fee or a cut of your savings. The review they’re selling is the same one you can request yourself for free. The Santa Cruz County Assessor says plainly that reviews are free and that you don’t need to hire an appraiser or a real estate agent. If you’d like help finding good comparable sales, call your Assessor’s office, or reach out to me and I’ll pull the January sales for your neighborhood at no charge.
What a Price Dip Means If You’re Thinking About Moving
For most of the longtime homeowners I work with, a softer market is a pricing and timing question, not a tax question. Your low Prop 13 base stays intact whether prices dip or not, and if you’re 55 or older, a Prop 19 base-year transfer can let you carry that base to your next home almost anywhere in California. A lower assessed value also has nothing to do with what a buyer will pay. Your sale price is set by the market, and the buyer simply gets reassessed at their purchase price.
If you’re weighing a move, it’s worth looking at the real numbers for your price range and neighborhood instead of the countywide median. My Best Move Report on the 60+ housing market in Silicon Valley is a good place to start, and if you’re on the buying side and just closed at a high price, my piece on selling RSUs to buy a house covers some of the other money decisions that come with it.
If you want a second set of eyes on whether your home might qualify for a Prop 8 review, or you’re trying to figure out whether now’s the right time to make a move, book a time with me or call 408-413-3087. I’m happy to help, and when the time comes, I’d love to help you make your next move the best one yet.
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Book My Downsizing Strategy Call →Frequently Asked Questions
Does a drop in my home’s value automatically lower my property taxes?
Only if your home’s market value on January 1 falls below its Prop 13 factored base year value. Assessors watch the market and sometimes reduce values on their own, but if you think you qualify, you can request a free review from your County Assessor. Most longtime owners are so far below market value that a dip won’t change their bill.
How do I know if I qualify for a Prop 8 reduction?
Find the assessed value on your annual notice or tax bill, then compare it with what similar homes near you sold for close to January 1 (and no later than March 31). If those sales suggest your home was worth less than your assessed value, you likely have a case worth submitting.
When is the Prop 8 deadline in Santa Clara County?
Santa Clara County mails value notices by the end of June. For the 2026-27 roll, the Assessor listed August 8, 2026 as the cutoff for informal requests. Formal assessment appeals are filed with the Clerk of the Board from July 2 through September 15.
When is the Prop 8 deadline in Santa Cruz County?
The Santa Cruz County Assessor accepts decline-in-value applications from July 2 through December 31 each year. If you want to file a formal assessment appeal as backup, the regular deadline is November 30, or the next business day when it falls on a weekend.
Can my assessed value go up more than 2% after a Prop 8 reduction?
Yes. While your home is in decline-in-value status, the 2% cap doesn’t apply, so your assessed value follows the market back up. It can never rise above your factored base year value, though, unless there’s a change in ownership or new construction.
Can I get a refund for prior years?
No. Only the most recent January 1 assessment can be reviewed, and Prop 8 doesn’t apply to supplemental assessments. That’s why it pays to check your value every summer when the notices arrive.
Do I need to hire someone to file a Prop 8 review?
No. Requesting a review from your County Assessor is free, and you don’t need an appraiser or real estate agent. Companies that charge a fee or a share of your savings are filing the same request you can file yourself.
Will a lower assessed value hurt my home’s sale price?
No. Your assessed value is only used to calculate property taxes. Buyers pay what the market supports, and the new owner is reassessed based on their purchase price.
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