Will California Proposition 40 Pass? Wealth-Tax Odds
Proposition 40 was certified for California's November 3, 2026 ballot on June 25. Prediction markets currently put No at 71.2% (-247 odds), while Yes is trading at 28.8% (+247 odds). DeFi Rate aggregates live pricing from Kalshi, Polymarket Global and Polymarket US for whether the one-time billionaire wealth tax passes. The feed displays rolling 30-day market volume and updates hourly using volume-weighted average pricing (VWAP).
Proposition 40 passage probability over time
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Chart settings
Proposition 40 odds on Kalshi vs. Polymarket
Current probabilities across platforms with liquidity indicators
NONo
Vol —
Spread 8.5%
Agg
71.2%↑ +3.8%California billionaire tax does not pass
P
71.5%
K
68.5%
U
63.0%
YEYes
Vol —
Spread 9.5%
Agg
28.8%↓ -3.8%California billionaire tax passes
U
38.0%
K
31.5%
P
28.5%
| Outcome | Aggregated | Spread | Volume | Kalshi | Polymarket | Polymarket US |
|---|---|---|---|---|---|---|
NO No California billionaire tax does not pass | 71.2% ↑ +3.8% | 8.5% | — |
Kalshi
68.5%
|
Polymarket
71.5%
|
Polymarket US
63.0%
|
YE Yes California billionaire tax passes | 28.8% ↓ -3.8% | 9.5% | — |
Kalshi
31.5%
|
Polymarket
28.5%
|
Polymarket US
38.0%
|
Arbitrage Scanner
Current cross-venue opportunities with fee calculations
Pairs (Venue-to-Venue)
| Outcome | Venue Pair | Leg A (Buy) | Leg B (Sell) | Gross Spread | After Fees | Actionable | Trade Now |
|---|---|---|---|---|---|---|---|
YE Yes California billionaire tax passes |
Polymarket
→
Polymarket US | Buy @ P 29¢ | Sell @ U 37¢ | +8.00% | +8.00% |
Yes | |
NO No California billionaire tax does not pass |
Polymarket US
→
Polymarket | Buy @ U 63¢ | Sell @ P 71¢ | +8.00% | +8.00% |
Yes |
Outcome Diff
| Outcome A | Outcome B | Venue | A Odds | B Odds | Diff | Strategy | Trade Now |
|---|---|---|---|---|---|---|---|
NO No |
YE Yes |
Polymarket | A 71.5% | B 28.5% | +43.00% | Buy spread | |
NO No |
YE Yes |
Kalshi | A 68.5% | B 31.5% | +37.00% | Buy spread | |
NO No |
YE Yes |
Polymarket US | A 63.0% | B 38.0% | +25.00% | Buy spread |
After-fee spreads apply the configured taker-fee model per side. Depth/slippage is not modeled in this scanner.
Methodology & Data Mapping
How we aggregate, normalize, and map cross-platform data
Default: Volume-Weighted Average Price (VWAP)
Weights each mapped market by its reported 24H USD volume at snapshot time. If volume is unavailable, we fall back to a simple average for that snapshot.
Use the VWAP/Simple toggle above the chart to switch aggregation views.
Kalshi: Official API (best bid/ask + last + 24H volume/liquidity when available).
Polymarket: Market data via their API (token prices + best bid/ask + 24H volume/liquidity when available).
Polymarket US: Gateway market data (yes/no prices + best bid/ask + market stats for volume/open interest where available).
Event data is updated hourly. Older history is downsampled.
Each event links one or more markets per provider. We normalize labels, map provider outcomes into a shared outcome list, and merge mapped markets where appropriate.
Cross-venue spread: Max–min difference across available venue probabilities for the same outcome.
Liquidity: Relative per-venue indicators based on provider liquidity fields (no depth/slippage modeling).
Arbitrage: Computed from best bid/ask when available (otherwise mid); after-fee spread applies the configured fee model only.
Valerie Cross
Valerie Cross is a reporter, editor, and prediction markets analyst with more than a decade of experience covering legal gaming and emerging financial markets. She joined DeFi Rate in 2026 after reporting on the rise of …
Cheryle Shepstone
Cheryle is Director of Content and Strategy at DeFi Rate. She oversees the prediction market research, platform reviews, and editorial methodology behind every guide—from primary source verification through final fact-ch…
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, Polymarket Global and Polymarket US. DeFi Rate aggregates first-party exchange data. Venue-level prices and activity are shown separately because the platforms report volume on different bases.
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.
- 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.
- 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.
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.