• Several billionaires have left or plan to leave California over its proposed wealth tax.
• The departures could mean that the state loses more in the long term than the one-time tax brings in.
• That's according to a working paper shared by a pair of Stanford economists.

Supporters of California’s proposed billionaire tax say it could raise about $100 billion.

But a new paper puts the takings closer to $30 billion and warns that the state could ultimately lose money if its richest residents flee.

Proposition 40, which goes before voters on November 3, would impose a one-time 5% tax on billionaires who were California residents on January 1, 2026, with their wealth valued at the end of the year. Most of the tax proceeds would go toward healthcare.

In a National Bureau of Economic Research working paper released this week, Stanford economists Benjamin Jaros and Joshua Rauh estimate the tax would collect between $28 billion and $36 billion — far short of supporters' $100 billion projection.

They point to billionaires moving away before the residency cutoff. Their estimate also assumes legal challenges could prevent California from collecting some of the remaining tax.

The authors identified seven billionaires reported to have left the state before the cutoff: Google cofounders Larry Page and Sergey Brin, investor Peter Thiel, director Steven Spielberg, Uber cofounder Travis Kalanick, investor David Sacks, and car loan tycoon Don Hankey.

Together, they accounted for nearly 30% of the wealth the researchers considered potentially taxable. The researchers noted that moving out of the state does not, by itself, settle someone's tax residency.

The authors' bigger concern is what happens afterward. California would collect the wealth tax only once, but billionaires who leave could stop paying state income taxes year after year.

If those departures and lost payments last, their model projects an average net loss of $38.9 billion. The researchers said they ran 100,000 simulations, and that in 85% of scenarios, losses outweighed revenues from the tax.

The forecast depends on who actually left and whether they stay away.

California's nonpartisan Legislative Analyst's Office offers a less stark view. It expects tens of billions in tax revenue and a possible ongoing drop of less than $1 billion a year in billionaire income-tax payments.

Brin is fighting the proposal on another front, too. He has given at least $102 million to Building a Better California, a group backing efforts to defeat or block Proposition 40. Two competing measures on the same ballot could keep Proposition 40 from taking effect, even if voters approve it.

While some billionaires have been vocal in their opposition to the tax, some have welcomed it. Nvidia CEO Jensen Huang told CBS News last month that being able to pay an estimated $8 billion over five years would be a "privilege."

In filings released this week, it was revealed that Meta CEO Mark Zuckerberg had considered moving out of California due to the tax, but ultimately decided to stay. To ensure that Zuckerberg has sufficient liquidity to pay without diluting his control of the company, Meta created a new class of shares.

Many economists back the plans. Six Nobel Prize winners — Daron Acemoglu, Abhijit Banerjee, Peter Diamond, Esther Duflo, Paul Krugman, and Joseph Stiglitz — signed a letter in September calling the proposal the "first opportunity for the people to start reining in the power of billionaires."

At the time, Acemoglu said it could counter years of tax avoidance by the very wealthy and curb their political influence. He said that while the proposal isn’t perfect, it "deserves support."

• Meta CEO Mark Zuckerberg considered moving out of California because of a proposed billionaire tax.
• Zuckerberg would get $20 billion in "immediate liquidity" if the billionaire tax passes.
• Meta made the offer to Zuckerberg to help keep him in California after he considered leaving.

Meta CEO Mark Zuckerberg considered moving out of California because of its proposed billionaire tax, Meta disclosed in a new SEC filing on Wednesday.

Next month, Californians will vote on Proposition 40, a one-time tax on the assets of the state's billionaires.

The filing said that Zuckerberg told a special committee formed by Meta that he was considering moving.

In response, the committee concluded that it was "critically important" for Zuckerberg to keep running Meta close to its Silicon Valley headquarters — particularly to its AI division, Meta Superintelligence Labs.

The filing said the committee got Zuckerberg to agree to remain in California or any other jurisdiction where Meta has its corporate headquarters for eight years, barring unforeseen circumstances.

As part of its efforts to ensure he can remain in charge as it raises more cash for its AI initiatives, the company is granting the Meta CEO a new stock class.

The shares would give Zuckerberg $20 billion in "immediate liquidity" to cover the tax by selling stock without losing control of Meta, if the tax passes. The new shares wouldn't add to Zuckerberg's net worth or increase his percentage ownership of Meta.

"The goal is to keep Mr. Zuckerberg continuing to lead the Company from California," the filing says.

Meta declined to comment. A person familiar with the matter said that the new class of shares, which totals $150 billion, is also intended to raise capital, compensate employees, and keep Meta's stock price on the right track.

Meta's filing showcases how tech billionaires are responding to the tax proposal. Some, including Google cofounder Sergey Brin and former CEO Eric Schmidt, poured hundreds of millions of dollars into attack ads against the proposal.

While Zuckerberg has taken a lower-key approach, it's clear he's been taking the proposed tax seriously.

The Meta CEO, who is worth about $240 billion according to Forbes, has multiple residences in California, including in Palo Alto and Lake Tahoe.

He also has a sprawling property portfolio outside the state, including a doomsday bunker in Hawaii, a waterfront mansion in Miami, and a castle in Ireland.

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• United CEO Scott Kirby says he's all for a nationwide wealth tax.
• Kirby said wealth inequality "has become a danger to our society."
• While Kirby doesn't want a state-by-state approach, California voters will soon vote on a proposed billionaire tax.

United CEO Scott Kirby says "wealth inequality has become a danger to our society."

That's why Kirby said he supports a nationwide wealth tax.

"We should have a national wealth tax — it won't work by state because people will just move," Kirby recently told The New York Times.

Kirby, who lives in the Chicago area near United's headquarters, was one of the highest-paid CEOs of a public company in 2025, according to Crain's Chicago Business. Kirby's 2025 total compensation was valued at over $32 million, according to United's filing with the Securities and Exchange Commission.

Wealth taxes are facing one of their biggest tests yet this November. Californians will vote on what, if approved, would become the world's first billionaire tax.

The fight is pitting some of the state's wealthiest individuals against the proposal. Google cofounder Sergey Brin alone has donated $102 million to a group seeking to undercut the proposed wealth tax by proposing competing initiatives that could effectively cancel it out.

In addition to a wealth tax, Kirby also said that inheritance taxes should be increased.

"We should have inheritance taxes that get close to 100 percent at some level," he said. "I would pay them."

Kirby's views may seem unusual among corporate leaders, but others are at least open to the idea of wealth taxes.

Nvidia CEO Jensen Huang recently reiterated his willingness to pay potentially billions of dollars if California's wealth tax goes into effect.

"I don't mind paying taxes," Huang said. "The more you make, the more taxes you pay, so I'm OK with it."

Huang, who famously got his start working at Denny's, said he worries about other things. Bloomberg estimates that the Nvidia CEO is now worth $180 billion, making him the ninth richest person in the world.

"The fact that I can afford to pay $8 billion in taxes over five years is a privilege," he said. "I'm not afraid of paying taxes. I'm just afraid of being poor."