Capital mobility undercuts wealth taxes as California's $24.7B risk looms

California's proposed 5 percent wealth tax on billionaires could reduce state tax revenues by an average of $24.7 billion across 71 percent of modeled scenarios, as capital mobility undercuts the measure's revenue projections. The one-time tax on residents with more than $1 billion in assets qualified for the November 2026 ballot after a filing by St. John's Community Health and SEIU-UHW, with 90 percent of proceeds earmarked for health care programs and the remainder split between education and food assistance.

"Higher taxation of wealth easily transmutes into lower total revenue and economic decline," said Richard B. McKenzie, retired economics professor at the University of California, Irvine, and co-author of "Quicksilver Capital: How the Rapid Movement of Wealth Has Changed the World."

The Stanford University-Hoover Institution analysis modeled 100,000 implementation scenarios and found California loses tax revenues in 71 percent of them, with an average net present value of negative $24.7 billion. California billionaires have already contributed more than $100 million to campaigns opposing the measure, while high-profile departures including Sergey Brin, Larry Page, and Peter Thiel illustrate the capital flight risk. The state's top individual income tax rate of 13.3 percent and corporate rate of 8.8 percent already rank among the highest in the nation, giving wealthy residents additional incentive to relocate.

The outcome of Proposition 40 will serve as a bellwether for wealth tax proposals nationwide, with implications for states and countries competing for mobile capital. McKenzie's 1991 book with University of Georgia economist Dwight Lee documented how falling relocation and communication costs have accelerated capital movement since the 1980s, when Margaret Thatcher and Ronald Reagan pressed for tax rate cuts that put competitive pressure on other governments to follow suit. The last comparable wave of tax competition saw U.S. states like Texas, Florida, and Tennessee attract corporate relocations from high-tax jurisdictions, a pattern that accelerated through the 2010s.

Cuban vs. Khanna: A $100 Million Fight

The debate over Proposition 40 came to a head on August 15 when billionaire investor Mark Cuban and Representative Ro Khanna (D-CA) clashed on X. Cuban raised four objections: illiquid capital makes the tax difficult for startup billionaires to pay, capital flight of existing businesses might increase, future startups might avoid California, and the state should address spending rather than taxation. Cuban noted that many newly minted billionaires are "cash poor, stock rich," with wealth tied up in private-company equity that has no ready market.

Khanna countered that roughly 72 percent of the 250 billionaires targeted hold their wealth in public stock rather than illiquid startup equity, and noted that Nvidia's Jensen Huang has voiced support for the measure. Tom Steyer, who placed third in California's June gubernatorial primary, called the tax "better than nothing" but "problematic in multiple ways," citing its one-time structure and narrow allocation of funds. Steyer instead proposed taxing commercial property at market value, which he estimated would raise more revenue over five years without triggering capital flight.

Tax Rates Fall as Capital Goes Digital

The California debate reflects a broader global dynamic. Income and corporate tax rates across the globe have continued their decline since the 1980s, though at a slower pace in recent decades. Digital technologies and artificial intelligence now offer the prospect of workforces of digitized "agents" that can roam the world unconstrained by national politics, further accelerating capital mobility. Email, the internet, and cloud computing have made it possible to move contracts, architectural plans, books, films, and games across borders in milliseconds.

New York Mayor Zohran Mamdani, whom Florida's Chamber of Commerce crowned "Florida's Economic Developer of the Year" for inducing city wealth to move south, illustrates the political risk of aggressive taxation. California Governor Gavin Newsom has opposed the state wealth tax while seeking cover by supporting a federal version, a likely nonstarter in Congress and at the White House.

Governments face a fundamental competitive problem: they are landlocked, while capital is footloose on a global scale. If Proposition 40 passes, the measure's actual revenue yield will test whether wealth taxes can survive in an era of quicksilver capital. For investors and businesses, the outcome will shape decisions about where to locate operations, hire talent, and allocate capital in the years ahead.

This article is for informational purposes only and does not constitute investment advice.