Californians will vote next Tuesday on Proposition 40, a ballot measure that would impose a one-time 5% tax on the state's billionaires. The levy would apply only to people whose primary residence was in California as of Jan. 1, 2026, and that cutoff has prompted several of the state's wealthiest residents to pack up and ship out to avoid the extra tax.

Travis Kalanick, the billionaire cofounder of Uber, was among them. Speaking in March, he said he had moved to Austin on Dec. 18, 2025—roughly two weeks before the tax would have applied to him. With an estimated net worth of $3.6 billion, Kalanick could have faced a $180 million tax bill.

"Just to be clear, on December 18, I moved to Texas. I don't know what's so specific about December 18, but let's just say it's prior to January," Kalanick told TBPN, alluding to the Jan. 1 cutoff. "Yeah, so I'm a primary resident of Texas."

Unlike Google cofounder Larry Page, who spent $173.4 million on two Miami estates, Kalanick decided to plant his new roots in Texas. Neither Texas nor Florida—the two destinations that recur throughout this exodus—levies a state income tax. Jeff Bezos made a similar move, leaving Seattle for Miami before Washington state passed a millionaires tax.

"I get a little bit [of] FOMO on like, these people going to Florida. I'm like, dude! Why so much Florida action?" Kalanick told TBPN. "Come on, homies."

Florida has drawn the biggest names in the exodus. "All the big guys [are] moving down here," Miami developer Robert Rivani previously told Fortune.

The move was not entirely abrupt for Kalanick. He told TBPN he had owned a home on Lake Austin, about 20 minutes outside the city, for roughly five years, drawn by the lake and his love of waterskiing. Craft Ventures cofounder David Sacks also relocated to Austin in December 2025.

Kalanick has been embracing the lake life. In June, he posted a video on X of what he called his "5-minute jet ski commute" across Lake Austin to the office of Atoms, the robotics company he now runs, formerly known as CloudKitchens.

Kalanick is one of several billionaires who left California between the measure's filing in October 2025 and the Jan. 1 deadline, according to a working paper by Stanford economists Benjamin Jaros and Joshua Rauh published this month. Together, they took about $540 billion, or nearly 30% of the wealth the tax could have reached, out of the state, according to the paper, which counts only publicly confirmed departures.

The tax would apply to billionaires' worldwide net worth but exclude real estate they own directly and most retirement accounts, according to the measure's text. If it passes, the bill would come due in 2027, though billionaires could spread payments over five years for an added charge. Ninety percent of the revenue would go to public health care services, including Medi-Cal, the state's Medicaid program, according to the Legislative Analyst's Office.

Passing Prop. 40 may not be enough

California would not be the first to test whether taxing the ultrawealthy drives them away. Britain scrapped its non-dom tax status last year—a rule that long let wealthy foreign residents avoid U.K. tax on overseas income—and billionaires have been leaving since, including property mogul David Reuben, who moved to Monaco this summer.

Supporters say the tax would bring in about $100 billion, but Jaros and Rauh put the figure closer to $30 billion once they account for the billionaire departures. Factor in the income taxes California stops collecting from the billionaires who left, and their simulations show the state losing an average of $38.9 billion.

Two competing measures on the same ballot could also essentially undo the tax. Proposition 41 would cancel any new state tax enacted after Jan. 1 whose revenue is exempt from California's spending limit, as Prop. 40's would be. Proposition 42 would ban new state taxes on owning personal property other than real estate, as well as certain retroactive taxes. If either outpolls Prop. 40, courts could rule that it cancels the wealth tax. Polling suggests all three could pass: in a September survey by the Public Policy Institute of California, 52% of likely voters said they'd vote yes on Prop. 40, 51% on Prop. 41, and 54% on Prop. 42.

The measure also doesn't break neatly along party lines. Gov. Gavin Newsom, a Democrat, opposes it, while Sen. Bernie Sanders (I-Vt.) and Rep. Ro Khanna (D-Calif.) have been among its most prominent champions.

A win next Tuesday would likely mean a trip to court. The measure gives opponents 60 days after approval to challenge it, and the backward-looking Jan. 1 residency date is an obvious target.

Kalanick's case is different. Because he says he left California before Jan. 1, his exposure to the tax would hinge on whether the state's tax authorities agree he truly made Texas his home—and the measure gives them broad power to audit billionaires they believe should have paid.

This story was originally featured on Fortune.com.