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Stanford study estimates Proposition 40 billionaire tax could raise far less

Supporters project $100 billion over five years, but a Stanford working paper estimates about $30 billion as billionaires depart.

Updated Oct 22, 2026 · 00:10 UTC4 reports

The short version

  • Proposition 40 would impose a one-time 5% tax on the net worth of California's roughly 200 billionaires, on the November ballot.[Business Insider · CBS News]
  • Supporters expect $100 billion over five years, 90% for healthcare, while a Stanford working paper estimates only about $30 billion.[CBS News · CBS News]
  • Seven billionaires have publicly left California, and Meta disclosed that Mark Zuckerberg considered moving; the company proposed share terms tied to staying in the state.[Business Insider · CBS News · CBS News · Wired]
  • Polling is close, with 46% of likely voters favoring and 43% opposing; Governor Gavin Newsom calls the measure flawed.[CBS News · CBS News]

Key facts

  • Proposition 40 would impose a one-time 5% state tax on the net worth of roughly 200 California billionaires.[Business Insider · CBS News]
  • Proponents expect $100 billion over five years, with 90% earmarked for healthcare.[CBS News]
  • A Stanford working paper estimates the measure may ultimately yield only about $30 billion.[CBS News]
  • Seven billionaires, including Peter Thiel, Larry Page and Sergey Brin, have publicly moved out of California since the tax was proposed.[CBS News · CBS News]
  • Meta disclosed in an SEC filing that Mark Zuckerberg considered moving out of California over the proposed tax.[Business Insider]
  • Meta proposed nonvoting shares that could give Zuckerberg about $20 billion in liquidity for taxes if the measure passes, with later sales tied to staying in California.[Business Insider · Wired]
  • A Citrin-Politico poll found about 46% of likely voters favor Proposition 40 and 43% oppose it.[CBS News]
  • Economists Daron Acemoglu and Joseph Stiglitz have endorsed the measure, citing increased venture funding in California since it was proposed.[CBS News]

What remains uncertain

  • The $30 billion figure is a preliminary working-paper estimate by Stanford economists, not an official revenue forecast.[CBS News]
  • Whether Proposition 40 passes is unknown, as a Citrin-Politico poll shows voters closely split.[CBS News]
  • The revenue impact is disputed: proponents project $100 billion, while Stanford economists project annual income tax losses of roughly $1 billion to $3.5 billion.[CBS News · CBS News]
  • Meta's share arrangement is described from its own SEC filing, so its terms are company-reported.[Business Insider · Wired]

Sources

Outlet counts describe coverage, not independent confirmation. Reports may share a wire service or original source.