California Proposition 40 Wealth Tax OddsWill the California billionaire wealth tax pass? Traders see a 24% chance

Tracking California Proposition 40 wealth tax odds

California’s billionaire wealth-tax initiative was certified for the November 3, 2026 statewide ballot on June 25 as Proposition 40, officially titled “Imposes One-Time Tax on Certain Taxpayers. Initiative Constitutional Amendment and Statute.” The active prediction markets now price whether voters will approve the measure—not whether it will reach the ballot. See the California Secretary of State’s qualified-measures list and official Proposition 40 voter guide.

The tracker above compares live prices from Kalshi and Polymarket Global. DeFi Rate aggregates first-party exchange data. Venue-level prices and activity are shown separately because the platforms report volume on different bases.

If you want to trade the Proposition 40 outcome rather than only follow its odds, compare political betting sites for ballot-measure coverage, costs and access.

What to watch before you trade

• Voter opinion: Watch California-specific polling that asks about Proposition 40’s actual ballot language rather than wealth taxes in general.
• Campaign activity: Endorsements, fundraising, advertising and the official arguments for and against the measure can affect voter awareness and market pricing. Our October 15, 2026 report examined Proposition 40’s polling and campaign-finance divide; its quoted market prices are a dated snapshot, not the live odds above.
• Competing measures: The official voter guide says Proposition 41 or 42 could prevent Proposition 40 from taking effect if either passes and receives more “yes” votes than Proposition 40. Compare California propositions 41 and 42 with Proposition 40 on the full ballot-measure board.
• Contract rules: Kalshi and Polymarket define resolution and early-determination procedures differently. Read the exact venue rules before trading.
• Liquidity and spread: Compare bid-ask spreads and venue-level activity rather than relying only on the aggregated probability.

Overview and key details of Proposition 40

Proposition 40 exceeded the 874,641-valid-signature requirement, became eligible on June 17 and was certified on June 25. It would impose a one-time tax of up to 5% on covered assets above $1 billion for taxpayers who were California residents on January 1, 2026. Covered assets include businesses, securities, art, collectibles and intellectual property. Real property and certain pensions and retirement accounts are excluded.

• Payment timing: The tax would be due in 2027. Taxpayers could spread payments over five years at an additional cost.
• Revenue use: Ninety percent would go to public health-care services; the remainder would support education, food assistance and tax administration. The revenue could not replace existing funding for those purposes.
• Fiscal estimate: The Legislative Analyst’s Office says the measure would probably raise tens of billions of dollars temporarily, while behavioral responses could reduce ongoing state income-tax revenue by less than $1 billion per year.
• Election: California voters decide the measure on November 3, 2026.

Political debate

Supporters—including the California Democratic Party, which endorsed Proposition 40 in August—argue that a one-time tax on billionaires would provide substantial funding for health care and other public services. Governor Gavin Newsom opposes the measure. Other opponents argue that valuation would be difficult, that affected taxpayers could change residency or investment decisions, and that California could lose future income-tax revenue. The official voter guide contains the state’s fiscal analysis and the formal arguments submitted by each side.

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What’s next

• Ballot qualification complete: Proposition 40 exceeded the valid-signature threshold on June 17 and was certified for the November 3 ballot on June 25.
• Now through Election Day: Supporters and opponents campaign over the measure’s fiscal impact, public-service funding and possible effects on taxpayer behavior.
• October 5, 2026: California counties begin mailing vote-by-mail ballots.
• October 19, 2026: The standard voter-registration deadline.
• November 3, 2026: Voters decide Proposition 40 in the statewide general election. If Proposition 41 or 42 also passes with more affirmative votes, Proposition 40 would not take effect.
• Market settlement: The active contracts resolve under each venue’s published rules. Kalshi’s market covers whether the one-time billionaire-tax initiative passes; Polymarket’s market resolves Yes if a qualifying proposition passes in the named election.