The property-tax advantage provided by California’s Proposition 13 became smaller for the average homeowner in six of the Bay Area’s nine counties between 2017 and 2025, according to an analysis of Redfin data. The 2026 tax roll was not available for the analysis.
San Francisco homeowners received an average tax reduction of about $9,000 under the law in 2025. Redfin estimated the city’s typical home value at nearly $1.6 million, while the average taxable assessment was slightly above $1 million. The market estimate was therefore about 52% higher than the assessment, a narrower difference than in 2017, when the market figure exceeded twice the assessed amount.
The pattern was not uniform across the region. In Cupertino, the difference between average market and assessed values increased from $1.2 million in 2017 to $1.5 million in 2025. The analysis found that Proposition 13 reduced the average homeowner’s tax bill there by more than $29,000 in 2025.
Approved by California voters in 1978, Proposition 13 generally bases property taxes on a home’s value when it was purchased, along with voter-approved local rate increases. The taxable amount can rise by no more than 2% annually. When a property is sold, its taxable value is reassessed.
Redfin data showed that assessed values rose more quickly than estimated market values from 2017 to 2025 in nearly every California county covered by the company’s records. In Santa Clara County, the average assessment increased from roughly $640,000, or 46% of an estimated $1.4 million market value, to nearly $1.1 million, or 57% of an estimated $1.9 million value.
Sarah Karlinsky of the UC Berkeley Terner Center for Housing Innovation said the tax system can create housing-market distortions by leaving long-term owners with relatively low taxable values and placing more of the tax burden on newer owners. Michael Lane, state policy director at SPUR, attributed changes in assessed values to rising home prices, low mortgage rates and increased sales during the pandemic period.
