Sergey Brin Is Spending Millions to Stop California's Proposed Billionaire Tax—Here's What's at Stake

Google co-founder Sergey Brin has poured $102 million into efforts to defeat California's proposed billionaire tax, which is a measure that could leave him facing an estimated $13 billion bill if voters approve it. With the 3rd November election approaching, Brin is also backing Proposition 42, a separate ballot measure that could prevent California from imposing the tax and restrict future wealth-tax proposals.

Brin's reported move to Nevada, alongside his property purchases outside California, has added another dimension to the debate over whether the proposed levy could accelerate an exodus of the state's richest residents.

What Is California's Proposition 40?

Proposition 40, also known as the 2026 Billionaire Tax Act, would impose a one-time tax of up to 5% on the covered assets of individuals whose qualifying assets exceed $1 billion. The measure is due to go before California voters on 3rd November.

Unlike a conventional income tax, the proposal targets accumulated wealth, including business interests, securities, art, collectibles, and intellectual property. Real estate and certain pensions and retirement accounts are excluded from the covered assets.

Under the proposal, 90% of the revenue would go towards healthcare, while the remaining 10% would fund food assistance or education-related programmes. The initiative is intended in part to help offset the effects of federal funding cuts on California's healthcare system and other public services.

The state's Legislative Analyst's Office estimates that the tax could generate tens of billions of dollars over several years. However, the final amount would depend on the assets subject to the levy and other factors affecting its implementation.

Brin's potential tax bill illustrates the scale of the dispute. With his fortune estimated at roughly $260 billion, a straightforward 5% calculation would produce a liability of about $13 billion. That is an estimate, not a confirmed assessment: his actual liability would depend on the value of his covered assets and the measure's detailed rules.

Insights Into Brin's Fight Against the Bill

Brin has contributed $102 million to Building a Better California, a political advocacy group opposing Proposition 40 and supporting other business-related policy initiatives. The contribution makes the Google co-founder one of the central financial figures in the campaign against the tax.

According to California campaign-finance disclosures reported by the Los Angeles Times and Fortune, his latest reported contribution included an additional $20 million donation in July. The opposition campaign has raised substantially more money than supporters of Proposition 40, giving opponents a significant financial advantage ahead of the vote.

The argument against the tax centres on its potential economic consequences. Critics contend that a levy on accumulated wealth could prompt billionaires to relocate, encourage businesses and investment to move elsewhere, and eventually reduce the state's income-tax revenue.

California Governor Gavin Newsom has also opposed the proposal, warning that the state risks losing revenue if wealthy taxpayers leave. However, supporters of the bill argue that asking billionaires to contribute a portion of their wealth is justified by the scale of wealth inequality and the state's funding needs.

What Is Proposition 42, and How Could It Stop the Tax?

Proposition 42 is a separate constitutional amendment on the same November ballot. It would prohibit new state taxes on the ownership of personal property, including financial assets, and restrict certain retroactive taxes. It would also nullify taxes enacted after 1st January 2026 that conflict with its provisions.

That distinction matters because Proposition 40 seeks to impose a one-time tax on covered billionaire assets, with the liability tied to circumstances specified in the initiative. Proposition 42 could therefore provide a legal route to blocking the wealth-tax measure.

California's official voter guide says that if Proposition 42 receives more affirmative votes than Proposition 40, courts could determine that the two measures conflict, potentially preventing Proposition 40 from taking effect even if it wins a majority of votes.

The measure's implications would extend beyond the current billionaire-tax fight. By restricting future taxes on financial assets and other personal property, Proposition 42 could limit the state's options for raising revenue in the years ahead.

The dispute is unfolding as some of California's wealthiest residents reassess their ties to the state. Brin has reportedly changed his residence to Nevada, a state without an individual income tax, and purchased a property worth about $51 million near Miami Beach in Florida.

These developments have fuelled speculation that wealthy Californians could shift their residences and investments to lower-tax states ahead of a possible levy.