California’s Prop 40 Debate Puts Residency, Valuation and Liquidity in Focus

California’s proposed one-time wealth tax has put residency, private-company valuations and liquidity at the center of planning conversations, including for clients far below the billionaire threshold. The proposal’s fate remained uncertain in early returns, but the questions it raised are likely to persist wherever states consider new ways to raise revenue.

Proposition 40 would impose a 5 percent tax on the net worth of billionaires who were California residents on January 1, 2026, with payment due in 2027. Early results had it trailing 57% to 43%, according to the Associated Press, which had not determined the outcome by Wednesday morning while ballots were still being counted.

Two other measures could affect whether the tax takes effect. Proposition 41 would require audits of new tax programs, while Proposition 42 would bar new state taxes on personal property and financial assets. Supporters of Proposition 40 have called the competing measures “poison pills”; if either receives more votes, it could effectively nullify the wealth tax.

Residency questions reach beyond billionaires

Debra Taylor, managing partner and chief tax strategist at Carson Wealth, said the debate has made residency a more prominent subject for clients who would not be covered by the proposal. “Prop 40 has moved residency from a footnote to a front-burner planning conversation,” she said. “Even clients nowhere near $1 billion are wondering how this policy may affect them.”

Business owners have been especially concerned, Taylor said, because residency decisions can intersect with where they live, locate a company and hire employees. Clients in other high-tax states are also watching for signs that similar proposals could emerge closer to home. Earlier this year, some California RIAs were already drafting exit plans as the proposal gained traction.

Taylor cautioned that relocation involves family circumstances, business connections and quality of life as well as taxes. A move after the proposal’s reference date would not change exposure under its terms: the measure looks to who lived in California on January 1, 2026. A change in residence could affect taxes in later years, but it would not alter that historical test.

That timing distinction matters for people considering a move. Decisions made to address a possible future tax burden may carry substantial personal and business consequences while leaving the proposal’s 2026 residency criterion untouched. An earlier report described a deal involving Meta that could shield Mark Zuckerberg from the proposed tax: Meta deal shields Zuckerberg from California wealth tax bill.

Valuation and recordkeeping could broaden the burden

The proposal’s administrative reach could extend well beyond the group expected to owe the tax. Taylor said every California resident who files a return would have to sign a certification under penalty of perjury. She also highlighted a proposed 10-year period for assessing tax related to 2026, compared with the usual four years. It remained unclear whether that longer period would apply only to billionaire filers or more broadly.

Her practical advice was to retain 2026 records well into the next decade. That could make documentation relevant even for households whose net worth is nowhere near the threshold, depending on how the measure’s requirements were interpreted and applied.

Valuing closely held businesses could be harder. The measure sets a default formula based on book value plus a multiple of average profits, and largely disallows discounts commonly applied to minority or illiquid ownership stakes. Taylor said that calculation could produce a value far above what a buyer would actually pay. A certified appraisal offers another route, but she described it as costly and said the appraiser could face personal penalties.

The proposal would measure net worth on December 31, 2026, a single date that may not reflect the value of illiquid holdings a year later. Founders and other owners can be asset-rich but short of cash. Selling shares to meet a wealth-tax bill could also trigger federal and state capital gains tax, potentially requiring a larger sale to cover both liabilities.

These issues are particularly relevant to households whose assets are concentrated in startup equity, private companies or partnership interests. Taylor’s concern is that an estimated tax bill could be based on a formula-driven valuation while the owner has limited access to cash and no straightforward way to sell a partial stake at that value.

State revenue trade-offs remain contested

California’s proposal is among the most ambitious state-level efforts to tax wealth, and some supporters have described it as the first measure of its kind aimed specifically at billionaires. Taylor expects the idea to keep resurfacing outside California. She pointed to federal changes that the Congressional Budget Office estimated would reduce Medicaid spending by $911 billion over a decade, along with new SNAP cost-sharing rules that shift expenses to states. States facing budget pressure may consider raising revenue, reducing spending or narrowing eligibility.

Supporters framed Proposition 40 as one possible fiscal response. Opponents argued that mobile wealth could leave California. That disagreement played out in a public split among California Democrats as the proposal advanced.

The state’s Legislative Analyst’s Office projected tens of billions of dollars in temporary revenue over several years, alongside a possible ongoing decline of less than $1 billion per year in income tax revenue from billionaires. A separate Stanford analysis suggested the tax could reduce state revenue, underscoring how estimates depend on responses by taxpayers and the effects on other sources of income.

Taylor said that if the proposal took effect, its retroactive reach and due-process questions could prompt legal challenges. International experience is mixed: of 12 OECD countries that had an annual wealth tax in 1990, only Norway, Spain and Switzerland still levy one in Europe. That record gives advisers and clients context, but it does not settle how a California measure would operate or how taxpayers would respond.

Planning amid an unresolved outcome

Taylor recommended that advisers document residency for clients who have moved or plan to move, maintain current valuations for closely held businesses, and test whether clients with concentrated private holdings could meet potential cash demands. She also suggested reviewing trust and gifting strategies under current rules and coordinating with clients’ other advisers.

For households comparing states, she said tax rates are only one part of the decision. They should also consider how readily tax rules can change through ballot initiatives, how much a state relies on its highest earners, and what compliance demands a similar measure might create. The state’s economy, talent pool, infrastructure and quality of life also belong in that assessment.

The immediate outcome will determine whether Proposition 40 moves from proposal to a practical tax question. Its wider effect is already visible in the planning work: residency evidence, business valuations, liquidity and the durability of a state’s tax structure have become harder to leave as afterthoughts.