California Billionaire Tax: Could Proposition 40 Cost the State Billions?

California’s proposed billionaire wealth tax is facing fresh criticism after a study suggested that the measure could raise substantially less revenue than its supporters expect, while potentially reducing the state’s income-tax collections over time.

Voters are scheduled to decide on Proposition 40 on November 3, 2026. The proposal would impose a one-time 5% tax on the assets of eligible billionaires. Supporters say it could generate around $100 billion over five years to help offset anticipated federal healthcare funding reductions. Critics argue that the final result could look very different.

The controversy goes beyond the headline revenue estimate. It raises questions about whether wealthy residents might leave California, how much income-tax revenue the state could lose as a result, and whether the measure would survive the legal challenges opponents expect.

For a state heavily reliant on high-income taxpayers, the stakes extend well beyond the billionaires directly affected.

Stanford Study Questions the $100 Billion Revenue Forecast

Supporters of Proposition 40 have promoted the measure as a way to generate substantial funding for healthcare programs facing pressure from federal spending changes.

However, a study by Stanford economists Benjamin Jaros and Joshua Rauh offers a more cautious assessment. Their analysis estimates that the tax could collect approximately $30 billion, significantly below the roughly $100 billion projected by the measure’s principal supporters.

The difference reflects concerns about the size of the tax base and the behavior of wealthy taxpayers before and after implementation.

According to the study, seven billionaires who had already left California represented approximately 30% of the state’s billionaire wealth. Their departures could reduce the amount of wealth available to tax under the proposal, weakening its potential revenue yield.

The researchers also examined the possible loss of annual income-tax revenue if former residents no longer pay California income taxes.

Their analysis estimates that these losses could reach $3.5 billion per year. If the losses persisted indefinitely, their present value could exceed the projected wealth-tax proceeds by approximately $39 billion.

These figures are estimates, not guaranteed outcomes. The final fiscal impact would depend on how many taxpayers leave, how their income and investments are treated under state law, and how the tax is implemented.

Nevertheless, the study raises a fundamental question: can a one-time tax deliver its promised benefits if the prospect of paying it changes the behavior of the people expected to finance it?

Could California Lose More Than It Gains?

The central criticism of Proposition 40 is that a tax designed to generate a large, immediate windfall could weaken an important source of recurring state revenue.

California collects income taxes from high earners, including people whose income comes from salaries, investments and business interests. If wealthy residents establish their tax residency elsewhere, the state could lose some of those future payments.

The extent of any losses is uncertain. A person's departure does not necessarily eliminate every California tax obligation, and the amount of revenue lost would depend on individual circumstances and applicable tax rules.

Still, the possibility matters because a one-time wealth tax and an annual income tax operate differently. The former seeks to collect revenue from a defined pool of assets, while the latter can generate revenue repeatedly as income is earned.

Critics argue that the state should evaluate the two effects together rather than focusing only on the initial amount the tax might collect.

Supporters counter that California needs additional resources to address healthcare funding pressures and that the wealthiest residents should contribute more toward public services.

The disagreement ultimately comes down to competing assumptions about how much the tax would collect, how taxpayers would respond and what the state would gain or lose over the longer term.

The Risk of a Wider Wealth Tax

Opponents also question whether Proposition 40 would remain a one-time measure.

The proposal is designed as a one-off tax, but critics worry that its adoption could encourage future campaigns to seek additional wealth taxes or expand the approach to other groups of affluent residents.

That concern is a political argument about what might follow, not proof that a broader tax has already been planned or approved.

Even so, the prospect of future tax changes could influence decisions made by entrepreneurs, investors and business founders considering where to establish their companies.

For people building businesses whose value depends on shares or other assets rather than a regular salary, the structure of a wealth tax can be especially consequential. A tax on assets may create a liability even when much of a person's wealth is tied up in a company rather than held in cash.

Critics say that uncertainty could affect investment decisions and encourage some founders to consider other states. Supporters, however, argue that concerns about potential departures should not automatically prevent policymakers from pursuing a tax aimed at raising revenue from the wealthiest households.

Whether these concerns translate into significant economic changes remains uncertain.

Legal Challenges Could Complicate the Measure

Proposition 40 could also face substantial legal challenges if voters approve it.

Jared Walczak, a senior fellow at the Tax Foundation, has argued that the measure raises serious constitutional questions. Critics contend that parts of the proposal could be vulnerable to litigation and that courts might ultimately block its implementation.

The outcome would depend on the specific legal claims, the arguments presented and how the courts interpret the relevant provisions of California law.

A successful challenge could delay collection while the state and the measure's supporters defend the tax. If a court invalidated the measure, the state could face a very different fiscal outcome from the one supporters have projected.

Opponents describe this as a particularly troubling scenario: the prospect of the tax could influence decisions by wealthy residents before any money is collected, while litigation could prevent the state from receiving the anticipated revenue.

That outcome is not inevitable. Legal disputes can have different results, and a court could reject some challenges or reach a narrower decision. But the prospect of litigation adds another layer of uncertainty to the proposal.

For voters, the legal question is therefore closely connected to the economic one. The potential benefits depend not only on how much the tax might raise, but also on whether it can be implemented and collected as intended.

Healthcare Funding Is at the Center of the Debate

Supporters of Proposition 40 argue that the state needs new resources to address the effects of federal healthcare funding reductions.

The measure's proponents estimate that it could generate approximately $100 billion over five years, with most of the proceeds intended to help offset those pressures.

Healthcare funding is a major concern because reductions in public financing can affect hospitals, clinics, healthcare providers and patients who depend on publicly supported programs. California's Medi-Cal program serves millions of eligible residents, including people with limited incomes.

Opponents do not necessarily dispute that healthcare funding is important. Their objection is that the proposed tax could be an unreliable way to finance those needs if revenue collections fall short or the state loses income-tax receipts.

This creates a difficult policy choice. California must weigh the potential value of additional funding against the risks associated with a tax whose economic effects remain contested.

The question is not simply whether the state needs money. It is whether Proposition 40 is likely to provide the resources supporters expect without creating offsetting costs.

California’s Tax Debate Could Have National Consequences

The debate has attracted attention beyond California because the state is often a testing ground for tax and economic policies that later influence national political discussions.

If Proposition 40 passes, advocates of wealth taxes in other states could point to the result as evidence that voters are willing to tax billionaire wealth to fund public services.

If it fails, opponents could argue that concerns about economic competitiveness, revenue uncertainty and legal risks have limited the appeal of such measures.

The outcome could therefore shape discussions ahead of the 2028 presidential election, particularly as Democrats continue debating how to address wealth inequality and fund public programs.

However, a vote in California would not automatically lead to a federal wealth tax or guarantee that other states would adopt similar policies. Any broader proposal would face its own political, economic and legal obstacles.

For now, California provides a case study in how wealth-tax proposals can divide voters, business interests, labor organizations and policymakers.

What Voters Should Consider Before Election Day

With Proposition 40 on the November 3 ballot, voters face competing claims about its likely effects.

Supporters emphasize the potential to generate substantial revenue for healthcare and argue that billionaires should contribute toward public needs.

Opponents focus on the possibility of wealthy residents leaving, reduced income-tax collections and legal disputes that could delay or prevent implementation.

The most useful way to assess the proposal is to separate projected outcomes from established facts. The $100 billion and $30 billion figures are competing estimates. The potential $3.5 billion annual income-tax loss is also a projection, and its impact would depend on how long any losses persisted.

The legal challenges remain prospective unless and until they are filed and resolved.

These uncertainties do not automatically settle the question in either direction. They do, however, make it important to examine the assumptions behind each forecast rather than relying solely on the largest revenue figure or the most alarming loss estimate.

The real test for Proposition 40 is whether it can deliver sustainable public benefits after accounting for taxpayer responses, implementation costs and legal risks. California voters will have to decide whether the potential gains justify those uncertainties.

Frequently Asked Questions

What is California Proposition 40?

Proposition 40 is a proposed ballot measure that would impose a one-time 5% tax on the assets of eligible billionaires in California. Voters are scheduled to decide on it on November 3, 2026.

How much money could the billionaire tax raise?

Supporters estimate that the measure could generate approximately $100 billion over five years. A study by Stanford economists Benjamin Jaros and Joshua Rauh estimates that collections could be closer to $30 billion.

Could the tax reduce California’s income-tax revenue?

Potentially. Critics argue that if wealthy residents leave California, the state could lose some of the income-tax revenue they would otherwise pay. The scale of any loss remains uncertain.

Why are some billionaires leaving California?

Tax policy is one issue in the broader debate over residency and investment decisions. The study cited in the debate identifies departures by seven billionaires, but individual decisions can have multiple causes.

Could Proposition 40 face legal challenges?

Yes. Critics have raised constitutional objections and warned that litigation could delay implementation. The outcome would depend on the claims brought before the courts and their rulings.

Would Proposition 40 automatically lead to a national wealth tax?

No. Even if the measure passes, any national proposal would require a separate political and legal process. California's decision could influence the debate, but it would not determine the outcome elsewhere.

Why is the tax linked to healthcare funding?

Supporters say the proposed revenue would help offset anticipated federal healthcare funding reductions, including pressures affecting Medi-Cal and other public healthcare services.

Follow developments in California tax policy, public finance and wealth-tax debates as voters prepare to decide whether the proposed billionaire tax offers a viable way to fund public services.