Google cofounder Sergey Brin bets $102 million to dodge a $13 billion tax bill as California billionaires head for the exit

Google cofounder Sergey Brin has poured $102 million into the fight against a proposed one-time tax on California's billionaires, a levy that could cost him about $13 billion if voters approve it in November.

According to a Fortune report citing campaign filings, Brin has given the money to Building a Better California, a political action committee and advocacy group that opposes the tax and backs pro-business policies and housing and infrastructure affordability.

Spending to block the measure has crossed $187 million, making Brin the largest single contributor, Fortune reported. Contributions supporting the measure stand at about $32 million.


What Proposition 40 proposes

Proposition 40 would impose a one-time 5% tax on the net worth of California's roughly 200 billionaires, payable over five years. Fortune reported that 90% of the revenue would go to the state's health care programme, and the rest to education, food assistance and administration.

The measure was put on the ballot by the labour union SEIU-UHW, which projects it will raise about $100 billion. The California Secretary of State confirmed it had qualified on 17 June, with 980,438 valid signatures.

Supporters, including the California Democratic Party and unions such as the Teamsters California and AFSCME California, say billionaires gained the most from recent federal tax cuts, while Congress cut funding for Medicaid, known in California as Medi-Cal.

Brin, whose net worth is nearly $260 billion according to Fortune, has likened the proposal to the socialism of his Soviet childhood. "I fled socialism with my family in 1979," he said in a statement in April, as quoted by Fortune. Former Google CEO Eric Schmidt and PayPal cofounder Peter Thiel have also given to groups opposing the measure.

Newsom sides with the opposition

California Governor Gavin Newsom has joined the tech billionaires in opposing the tax. He has argued that it would erode the state's tax base and cut funding for education, childcare, firefighting and policing, Fortune reported.

California is the most populous US state, with a GDP of about $4 trillion, roughly the size of the UK's economy. Fortune noted that it also has the country's highest poverty rate, with 18% of residents below the poverty line, partly because of its high cost of living. That gap has made the state the centre of the debate over the "K-shaped economy", where the fortunes of the wealthy and everyone else move apart.

Billionaires are already moving

Fortune reported that Brin now lists Nevada as his residence in state records, and that he reportedly bought a $51 million home near Miami Beach in March. His Google cofounder Larry Page has moved several assets out of California. These include Koop, his family office, which was incorporated in Delaware in December 2025, and the ocean science nonprofit Oceankind, founded by Page's wife Lucy Southworth.

Six billionaires are expected to leave the state: Brin, Page, Thiel, car loan magnate Don Hankey, former Uber CEO Travis Kalanick and director Steven Spielberg. Fortune reported that together they would have generated about $27 billion in tax revenue, around one-fourth of the $100 billion the tax is expected to raise over five years.

Will a wealth tax drain California?

The evidence is not clear, according to Fortune. It cited a National Bureau of Economic Research working paper from May, which found that California's billionaires paid $4.1 billion in income tax last year, about 0.2% of their combined $2 trillion net worth. Even if every billionaire left, it would take about 25 years for the lost income tax to cancel out the $100 billion, the paper found.

If a quarter of the state's wealthiest left, it would take a century. The authors described the tax as small compared with the billionaires' wealth gains but large compared with what they now pay.

The state's own estimates are more cautious. The official ballot summary, based on analysis by the Legislative Analyst's Office, projects a temporary revenue gain of tens of billions of dollars. It also warns of a possible ongoing loss of less than $1 billion a year in income tax revenue from billionaires.

Opponents have also put two countermeasures on the November ballot, Propositions 41 and 42. If either gets more votes than Proposition 40, the billionaire tax could be nullified in part or in full, according to the state's ballot analysis.

A recent poll by NBCUniversal Local and the Telemundo Station Group found 48% of likely voters in favour of Proposition 40 and 38% against. That is a lead, but still short of a majority.