Google co‑founder Sergey Brin has donated more than $100 million — plus an additional $20 million to Build A Better California — to oppose Prop 40, a proposed one‑time 5% tax on the net worth of about 200 California billionaires. At an estimated net worth of $267 billion, Brin could have faced roughly $13.3 billion in liability under the measure. Governor Gavin Newsom opposes the state initiative in favor of a national approach, while competing ballot measures and potential federal Medicaid cuts complicate the November showdown.
Sergey Brin Pumps $100M+ Into Fight Against California’s Prop 40 — A Billionaire Tax Battle
Google co‑founder Sergey Brin has spent more than $100 million opposing California's proposed "billionaire tax," Prop 40, a one‑time 5% levy on the net worth of roughly 200 billionaires that would raise funds for state healthcare programs. According to filings, Brin also contributed an additional $20 million to Build A Better California as part of that effort. At Brin's estimated net worth of about $267 billion, the measure could have cost him an estimated $13.3 billion.
What Prop 40 Would Do
Prop 40 would impose a one‑time 5% tax on the worldwide net worth of qualifying billionaires who reside in California. The revenue is earmarked primarily for state healthcare programs, but the ballot measure faces legal and political questions and several competing initiatives that could alter or block its implementation.
Political Response and Competing Measures
Sergey Brin, co-founder of Google, at a dinner at the White House in Washington D.C. on September, 2025. Bloomberg via Getty Images
California Governor Gavin Newsom has publicly opposed Prop 40 and instead urged a national billionaires' tax. In a Substack post, Newsom argued that current rules let some ultrawealthy individuals borrow against stock portfolios while reporting little or no taxable income:
"Today, the office worker can shoulder a higher tax rate than the heiress. We should end the 'tax‑free lifestyle loan,' the gimmick that lets the ultra‑wealthy borrow against their stock portfolios while reporting no taxable income."
Prop 40 is scheduled for California's November ballot, but it faces rival measures — including one that would require audits of programs funded by new state special taxes — that could undercut or delay any revenue collection.
Broader Context
The debate comes as expected federal budget changes could reduce funding for California programs. Analysts project California's Medicaid program (Medi‑Cal) could lose as much as $30 billion in federal support under proposed federal budget cuts, an outcome that complicates the state's fiscal planning.
Google headquarters in New York (pictured). (Christopher Sadowski) Christopher Sadowski
Responses From the Wealthy
Some wealthy Californians have taken steps that suggest tax‑avoidance strategies or relocation: Meta founder Mark Zuckerberg reportedly purchased a $170 million mansion near Miami this year, and billionaires such as Peter Thiel, Travis Kalanick and Google co‑founder Larry Page have left California. Others, including Nvidia co‑founder Jensen Huang, publicly say they are "perfectly fine" paying a billionaire tax.
Why It Matters
The Prop 40 fight highlights growing national tensions over how to tax extreme wealth, the role of ballot initiatives in shaping tax policy, and the fiscal pressures states face when federal support shifts. The outcome in November could influence both state and national debates about taxing the ultra‑wealthy.
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