Prop 13's Big Bay Area Discount Is Still Huge — But in Some Places, It's Shrinking

For nearly half a century, California's Proposition 13 has been the quiet force behind some of the biggest tax breaks in the country. By capping how much a home's assessed value can rise each year, it lets long-term owners pay property taxes on a fraction of what their homes are actually worth. But new data suggests that gap — the very thing that makes Prop 13 so valuable — is starting to narrow in parts of the Bay Area.

The Basics: A Widening (or Narrowing) Gap

Under Prop 13, homes are reassessed at market value only when they're sold or newly built. After that, the assessed value — the number your tax bill is based on — can climb by no more than 2% a year, no matter how fast the local housing market takes off. Over time, that creates a growing distance between what a home is actually worth and what the county says it's worth for tax purposes.

That distance is the whole ballgame. The bigger the gap, the bigger the tax savings.

San Francisco's Shrinking Subsidy

In San Francisco, that gap is still enormous — just a little less enormous than it used to be. A Chronicle analysis of Redfin data found that Prop 13 saved the average San Francisco homeowner roughly $9,000 in property taxes in 2025. The average home in the city was valued near $1.6 million that year, but its average assessed value — the figure actually taxed — was just over $1 million, meaning the typical home was worth about 52% more on the open market than it was to the assessor's office.

Here's the twist: that gap is actually smaller than it was in 2017, the earliest year with reliable Redfin data, when market values were running more than double the average assessment. San Francisco isn't alone — in six of the nine Bay Area counties, the space between market and assessed values shrank between 2017 and 2025.

Data for the 2026 tax roll wasn't yet available, but given the sharp run-up in San Francisco home values this year, that gap has likely widened again.

Why the Gap Is Closing (For Now)

Across most of California, assessed values have been growing faster than market values since 2017 — meaning more of a typical home's worth is being taxed than it once was. In Santa Clara County, for instance, the average assessed home value sits around $640,000, just 46% of the average estimated $1.4 million market value.

The explanation isn't a change in the law — it's the market cycle. The relationship between assessed and market values behaves like an accordion, stretching wide during hot markets and squeezing narrower when price growth slows or stalls, since the 2% assessment cap keeps climbing steadily even as market values plateau.

Not Everywhere: Santa Clara County's Outlier

The trend isn't universal. Cupertino bucked it entirely — the gap between market and assessed values there actually grew, from $1.2 million in 2017 to $1.5 million in 2025. That translated into serious savings: Prop 13 shaved more than $29,000 off the average Cupertino homeowner's tax bill in 2025, among the largest subsidies in the region.

The Takeaway

None of this means Prop 13's benefits are disappearing. Even with a narrower gap, San Francisco homeowners are still saving thousands of dollars a year, and the law's fundamental mechanics haven't changed. What's shifting is the pace: after years of runaway home-value growth outstripping the 2% assessment cap, some parts of the Bay Area are seeing that dynamic even out — a reminder that Prop 13's biggest windfalls have always tracked the rhythms of the housing market itself.

Based on reporting by Christian Leonard, San Francisco Chronicle (Sept. 13, 2026), analyzing property data from Redfin.