California Prop 40: The Billionaire Tax Vote Explained
California voters will decide on November 3 whether to impose a one-time 5% tax on the net worth of the state's billion
aires. Proposition 40 is projected by its backers to raise about $100 billion, mostly for health care, but economists, the state's own analysts and opponents disagree sharply about how much it would actually bring in. Polls are mixed, opposition spending is far larger than support, and two other measures on the same ballot could cancel it even if it passes.
Key takeaways
- Prop 40 would tax residents worth more than $1 billion once, at 5%, on wealth held as of January 1, 2026. About 200 people are estimated to be covered.
- Revenue estimates run from about $40 billion (a Hoover Institution study, before losses) to $100 billion (the sponsoring union).
- Props 41 and 42 are competing measures. If either gets more "yes" votes than Prop 40, the billionaire tax can be nullified.
What would Prop 40 do?
It would impose a one-time tax of 5% on the net worth of California residents and trusts worth more than $1 billion. Eligibility is fixed by residency on January 1, 2026, so moving after that date does not remove the liability. Taxpayers between $1 billion and $1.1 billion would pay a lower rate. The tax covers assets including stocks, privately held businesses, cash, art and intellectual property, not just income, and includes unrealized gains.
The money would be spent mostly on health care. About 90% would go to public health care services, with the rest going to education, food assistance and administering the tax. The measure also exempts the revenue from constitutional school-funding and spending-limit rules. The sponsor, SEIU-UHW, a health-care workers' union, says the goal is to replace federal health funding cuts, including to Medi-Cal, the state's Medicaid program that covers about 14 million people.
How much would it raise?
The answer depends on who you ask.
| Source | Estimate |
|---|---|
| SEIU-UHW (sponsor) | About $100 billion over five years |
| State Legislative Analyst's Office | A temporary increase of "tens of billions" over several years, plus a possible ongoing loss of under $1 billion a year in income tax revenue |
| Hoover Institution (March study) | About $40 billion collected, but California worse off by about $25 billion after lost income tax from departing billionaires |
The gap comes mainly from one question: how many billionaires leave or restructure before paying, and how much income tax the state loses if they do. The ballot arguments reflect it. Supporters call the tax a modest, one-time charge on about 200 people. Opponents argue it will cost the state revenue, shortchange schools and give the legislature room to change the measure later without voter approval.
Who is for it, who is against it, and who is paying?
The two sides don't follow party lines neatly. Senator Bernie Sanders and the California Democratic Party support Prop 40. Governor Gavin Newsom, a Democrat, and former congresswoman Katie Porter oppose it. Nvidia CEO Jensen Huang has said he is "perfectly fine" with it. Some unions have opposed it, saying other state spending should be priorities too. Former Vice President Kamala Harris and Speaker Emerita Nancy Pelosi had not taken a position as of mid-October.
The money gap is large. Opponents have raised more than $205 million, according to CalMatters' campaign-finance count, and the San Francisco Chronicle puts the figure near $259 million, about eight dollars for every dollar raised by supporters. Google co-founder Sergey Brin is the largest donor, with more than $100 million to the group Building a Better California, which also backs the two competing measures. Supporters, largely funded by SEIU-UHW, have spent about $22 million.
What do the polls say?
They disagree. A September Public Policy Institute of California survey found 52% of likely voters in favor and 46% opposed. A late-September poll from the Independent Voter Project showed opposition ahead by 4 points, and the latest from the Manhattan Institute, a conservative think tank, put "no" ahead by 15. Mark Baldassare, the PPIC survey director, said supporters have "a lot of work to do." Treat the range as the honest answer: the outcome is uncertain, and spending against the measure has been running at more than $1 million a day.
Will billionaires leave?
Some already have. Google co-founders Larry Page and Sergey Brin and investor Peter Thiel were reported to have moved out of California before the January 1 cutoff, while others have shifted residences or business assets. Joel Slemrod, a University of Michigan tax economist, notes there is little evidence to judge how billionaires would react because the proposal is unique. Kirk Stark, a UCLA tax law professor, says the worry is that wealthy people will expect the tax to be repeated.
Defenders point to the other side of the ledger. As Fortune reports, a group of Nobel laureates contends the tax will not doom Silicon Valley, noting that California has drawn about 80% of new US venture funding this year, up from about 50% before 2025. Both claims are being argued with limited data.
What are Props 41 and 42?
They are counter-measures placed on the ballot by Brin's group. Proposition 42 would amend the constitution to forbid retroactive taxation, which would block Prop 40. Proposition 41 would count some new state taxes toward the state's education and spending-limit rules. If either receives more "yes" votes than Prop 40, courts could block the billionaire tax even if it passes. A PPIC survey found majority support for all three, which makes the combination unpredictable.
What does it mean for markets and investors?
California is not a typical state budget. The top 1% pay nearly half of the state's income taxes, according to Fortune, so the state's revenue is sensitive to a small group of wealthy residents and to capital gains. Three things matter beyond the vote: the precedent of taxing unrealized wealth, which other states and countries are watching; the reliability of California's income tax base if wealthy residents leave; and how the state would fund health care if federal money shrinks. These themes connect to the wider pressure on public finances we covered with the federal debt passing $40 trillion and Ray Dalio's warning about debt and fiscal strain. Nothing in Prop 40 forces investors to sell anything, but the outcome will be read as a signal about how far US states will go to tax wealth.
A Vote Where Even the Revenue Is Contested
On most ballot measures, the argument is about whether the policy is good. Here the disagreement starts one step earlier, at how much the tax would collect. Supporters say $100 billion. Hoover says $40 billion and a net loss. The state's analysts say tens of billions with an offset. Add the competing measures, a late-moving polling picture and an unprecedented tax on unrealized wealth, and the result on November 3 is hard to call. The vote will settle the law. It won't settle the economics.
FAQ
What is Proposition 40? A California ballot measure that would impose a one-time 5% tax on the net worth of residents worth more than $1 billion, with about 90% of the money going to health care.
How much would Prop 40 raise? Estimates range from about $40 billion (Hoover) to $100 billion (the sponsor). The state's analysts expect tens of billions over several years.
Can Prop 40 be blocked even if it passes? Yes. If Proposition 41 or 42 gets more "yes" votes than Prop 40, courts could block the billionaire tax.
Sources: California Legislative Analyst's Office, California Secretary of State voter guide, CalMatters, San Francisco Chronicle, Fortune, Forbes/Yahoo, AFP, Public Policy Institute of California, Hoover Institution, as of October 18, 2026. Polls and fundraising figures change quickly. This article is for informational purposes only and does not constitute investment, tax or legal advice.
