Prediction markets swing on California billionaire tax

California’s proposed billionaire tax is headed toward a ballot-qualification deadline, but prediction markets are moving from near-certainty to near-skepticism. As Kalshi and Polymarket traders price a turnout outcome against the tax, the debate is also being

For a moment last week, California’s billionaire tax looked like a near lock—priced by traders at better-than-80% odds of making the November ballot.

But by Wednesday, June 17, the pricing had broken. Kalshi and Polymarket showed the outcome hovering just under a coin flip on whether the tax proposal would reach voters. The shift was fast enough to be felt in the market: both platforms had taken a major dive after separate reporting that California Gov. Gavin Newsom was working to kill the tax. Before that news landed, both markets were above 80%.

Newsom’s fight is arriving at the deadline’s edge. There is a June 25 deadline to certify whether the proposal will be on the November ballot. By Wednesday afternoon, traders were far less confident about public support. Kalshi placed the proposal’s odds at just over a 19% chance. Polymarket pegged it at just an 18% chance.

Under the proposal, California residents and certain trusts with net worth of $1 billion or more would face a one-time tax for tax year 2026. The full rate would be 5% for those at or above $1.1 billion, with a phase-in for individuals between $1 billion and $1.1 billion.

Both prediction markets are structured around whether the initiative passes—meaning it would still require only a simple majority of Californians to vote in favor, assuming the proposal actually makes the ballot.

The numbers don’t tell the whole story, though. What makes the tax especially contentious is that it would apply retroactively to billionaires living in California as of January 1, 2026. Supporters say the policy targets concentrated wealth. Critics point to the timing—one reason market pricing appears to be weakening on voter acceptance.

The proposal’s retroactivity has also fed a separate headline fight about who moved first. Google cofounders Sergey Brin and Larry Page moved assets out of California months before supporters even finished gathering signatures for the proposal.

California, home to more billionaires than any other state, is therefore carrying one of the biggest wealth tax debates so far.

The push and pull inside the Democratic coalition is also sharp. The SEIU-UHW, a healthcare workers union, is pushing the tax. Planned Parenthood affiliates and the California Teachers Association—one of the state’s largest teachers unions—are lined up against it.

And while the ballot-qualification fight may look like the end of the road for one contest, it could be only the beginning. Ballot qualification likely won’t end the fight.

“Building a Better California. ” an anti-wealth tax political action committee. has already started pouring money into competing measures that could neutralize or greatly limit the proposed billionaire tax. Brin has donated $82 million to the committee. Stripe cofounder Patrick Collison donated $7 million. Former Google CEO Eric Schmidt kicked in roughly $3 million more. All told, “Building a Better California” has brought in $129 million from just 10 donors.

One of the committee’s competing initiatives includes a retirement-and-personal-savings measure that would prohibit new taxes on ownership or control of personal property and ban retroactive taxes. Under state law. if both initiatives secure a simple majority of votes. the one that receives the most votes would win.

Another front is being funded by individuals tied to tech and crypto. Ripple Labs and Chris Larsen—its executive chairman and cofounder—each donated $5 million to “Golden State Promise,” a group set up to oppose the proposed tax.

Silicon Valley investor Ron Conway donated $100,000 to “Stop the Squeeze,” another opposition group. In March, Conway told investor Jack Altman that he worried the tax could pass if it ever reached voters. Conway said. “our job is to get Gavin to negotiate this.” He added. “We must keep this off the ballot. ” during an episode of Altman’s “Untapped” podcast. “So a whole bunch of work has to happen for that.”.

California billionaire tax Gavin Newsom Kalshi Polymarket prediction markets ballot deadline June 25 November ballot retroactive tax SEIU-UHW Planned Parenthood affiliates California Teachers Association Building a Better California Golden State Promise Stop the Squeeze Sergey Brin Larry Page Patrick Collison Eric Schmidt Chris Larsen Ron Conway