The California wealth tax heading to voters as Proposition 40 is shaping up as one of the most closely watched items on the November 3 ballot.
Prediction markets on both Polymarket and Kalshi see the measure as more likely to fail than pass, pricing the California billionaire tax as a modest underdog with more than a month still on the clock.
Governor Gavin Newsom's public opposition and two competing "poison pill" initiatives have only added to the uncertainty around whether this billionaire tax California voters are considering will actually take effect.
| 🏢 Platform | 🏷️ Pick | Price | 🤑 Profit on $100 | 📈 Trade It |
|---|---|---|---|
| Polymarket | Prop 40 | YES (34¢) | $194.12 | Trade it on Polymarket! |
| Polymarket | Prop 40 | NO (67¢) | $49.25 | Trade it on Polymarket! |
| Kalshi | Prop 40 | YES (33¢) | $203.03 | Trade it on Kalshi! |
| Kalshi | Prop 40 | NO (68¢) | $47.06 | Trade it on Kalshi! |
Below you'll find a full breakdown of the current California wealth tax odds across the exchanges, but if you want to jump straight in, check out the latest Polymarket promo code or the Kalshi promo code.
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California Billionaire Tax Prop 40 Polymarket Odds: Top Trading Contracts
Polymarket prices event contracts between 1¢ and 99¢, with each cent mapping directly to an implied probability. A "Yes" share on whether Prop 40 passes settles at $1.00 if California voters approve the wealth tax and $0 if they reject it, and traders can buy or sell their position at any point before the November 3 election closes the market.
Prop 40 Passage (YES 34¢ / NO 67¢)
Polymarket traders are pricing in a 34% chance that the California billionaire tax passes, a clear underdog position heading into the final stretch. That skepticism tracks with the opposition lined up against Prop 40, including Governor Newsom, the California Teachers Association, and a well-funded "poison pill" campaign bankrolled in part by Sergey Brin.
Still, a 34¢ price leaves real room for movement. The measure only needs a simple majority, and the SEIU-UHW-backed campaign has already shown it can turn out signatures and media coverage, so a late swing toward "Yes" is far from off the table if health care messaging breaks through before Election Day.
California Billionaire Tax Prop 40 Kalshi Odds: Top Trading Contracts
Kalshi runs on the same basic mechanics: event contracts trade from 1¢ to 99¢, a "Yes" position pays out $1.00 if Prop 40 passes and nothing if it fails, and the contract resolves once California's Secretary of State certifies the official election results.
Prop 40 Passage (YES 33¢ / NO 68¢)
Kalshi's board shows an almost identical read, with the exchange's own odds feed pegging the California wealth tax at a 35% chance of passing. That's close enough to Polymarket's number that neither platform is picking up a meaningfully different signal from its trader base right now.
Both exchanges are effectively betting against history: no U.S. state has ever enacted a standalone wealth tax on net worth, and the retroactive Jan. 1, 2026 residency trigger has already pushed a visible number of billionaires to rethink their California ties before voters even go to the polls.
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How Polymarket and Kalshi Compare on the California Wealth Tax
Polymarket and Kalshi are telling nearly the same story on Prop 40. Both boards have the measure losing more often than not, with Polymarket at NO 67¢ and Kalshi at NO 68¢, a one-point gap that's well within normal noise between two separate order books.
On the "Yes" side, Polymarket sits at YES 34¢ against Kalshi's YES 33¢. Neither platform has broken away from the other, which suggests both trader bases are drawing on the same public polling and campaign-finance disclosures rather than picking up on distinct, platform-specific information.
The tightness of the spread also means there's little obvious arbitrage between the two exchanges right now. If that gap widens as Election Day approaches, usually a sign one platform's traders are reacting faster to new polling or ad spending, it could be worth watching for a mispricing before the board tightens back up.
California Wealth Tax Price Analysis: Market Price Influencers
The biggest swing factor for the California billionaire tax is the two counter-initiatives sharing the same ballot. Propositions 41 and 42, funded in large part by Google co-founder Sergey Brin, are designed so that if either outpolls Prop 40, the billionaire tax is nullified even if it also clears a simple majority on its own.
Campaign spending is lopsided toward opposition. Groups aligned with Newsom, the California Teachers Association, and Planned Parenthood's state chapter have joined the fight against the measure, while the SEIU-UHW-backed "Billionaire Tax Now" coalition is leaning on a health care funding message to keep its yes-vote coalition intact, and the wealth tax in California has already become one of the most expensive ballot fights in the state's history.
Watch the California Democratic Party's late-cycle messaging and any fresh independent polling in October. The party's executive board already endorsed Prop 40 over Newsom's objections, and a visible split like that at the top of the ticket is exactly the kind of headline that can move a market pricing a close-but-unfavored outcome.
| 🏢 Platform | 🏷️ Pick | Price | 🤑 Profit on $100 | 📈 Trade It |
|---|---|---|---|
| Polymarket | Prop 40 | YES (34¢) | $194.12 | Trade it on Polymarket! |
| Polymarket | Prop 40 | NO (67¢) | $49.25 | Trade it on Polymarket! |
| Kalshi | Prop 40 | YES (33¢) | $203.03 | Trade it on Kalshi! |
| Kalshi | Prop 40 | NO (68¢) | $47.06 | Trade it on Kalshi! |
How to Trade the California Billionaire Tax on Prediction Markets
Ready to take a position? Check out the best political trading apps and start trading event contracts in minutes on either exchange.
Polymarket
- Read a comprehensive Polymarket review to understand how this exchange operates.
- Follow this guide to trading on Polymarket to learn how to buy your first "Yes" or "No" contract.
- Monitor the relevant tab on Polymarket to stay ahead of the live order book movements.
📝 POLYMARKET TERMS & CONDITIONS
18+ Only. Restrictions and eligibility requirements apply. Not available in all jurisdictions. Trading is risky. 100% loss can occur. See polymarket.com/tos for more information. The Polymarket US App serves as an independent software provider and affiliate of Polymarket US and Polymarket Clearing, the CFTC-regulated exchange and clearing organization.
Kalshi
- Read a comprehensive Kalshi review to understand how this exchange operates.
- Follow this guide to trading on Kalshi to learn how to buy your first "Yes" or "No" contract.
- Monitor the relevant tab on Kalshi to stay ahead of the live order book movements.
📝 KALSHI TERMS & CONDITIONS
Certain limitations apply. The offer is available to new users only, subject to the terms and conditions. 18+ only. Restrictions and eligibility requirements apply. Event contract trading involves significant risk and is not appropriate for everyone. Please carefully consider if it is appropriate for you in light of your personal financial circumstances. Kalshi products are not available in all jurisdictions. See kalshi.com/regulatory for more information. Not available in AZ, IL, MA, MD, MI, MT, NV, OH, and WA.
California Wealth Tax (Prop 40): Final Thoughts
Right now the market sees Prop 40 as a real possibility but not the favorite, with both Polymarket and Kalshi clustered in the mid-30s on "Yes." That's a measure the crowd views as genuinely competitive rather than a foregone conclusion either way.
The presence of two nullifying counter-initiatives on the same ballot makes this one of the more structurally unusual races prediction markets have priced this cycle, and the next few weeks of campaign spending and polling will likely decide which way the board breaks.
California Wealth Tax FAQs
What Is the Wealth Tax in California?
In short, the wealth tax in California is Proposition 40, the 2026 Billionaire Tax Act. If voters approve it this November, it would impose a one-time 5% excise tax on the net worth of California residents worth $1 billion or more, with most of the revenue earmarked for state health care programs and the rest split between education and food assistance.
How does the billionaire tax California voters are deciding on actually work?
The billionaire tax California lawmakers put on the ballot applies to anyone who was a California resident on Jan. 1, 2026, and whose net worth still clears $1 billion on Dec. 31, 2026. It's calculated on worldwide assets, not just California-based wealth, and qualifying taxpayers can spread payment over five annual installments with interest.
When does the Prop 40 prediction market resolve?
Both the Polymarket and Kalshi contracts close around the Nov. 3, 2026 election and settle once California's Secretary of State certifies the statewide results. A "Yes" share on either platform pays out $1.00 if the measure is certified as passed, and nothing if it fails or is nullified by a competing initiative.
What is the wealth tax in California worth to the state budget if Prop 40 passes?
If Prop 40 passes, the wealth tax in California is projected by the Legislative Analyst's Office to temporarily add tens of billions of dollars in state revenue, collected over several years as affected billionaires pay their obligations. Supporters say that money is critical to backstop health care funding, while opponents argue it risks a longer-term exodus of wealthy residents and their tax dollars.
Why might the billionaire tax California voters approve still not take effect?
Two rival measures, Propositions 41 and 42, are built to override Prop 40: if either earns more "Yes" votes than Prop 40 does, the billionaire tax is nullified even though it also passed. That structural wrinkle is one of the main reasons both prediction markets have Prop 40 priced as an underdog rather than a clear favorite.
Do Polymarket and Kalshi price the California wealth tax the same way?
Almost. As of this writing, Polymarket has the measure at 34¢ "Yes" and Kalshi has it at 33¢, a one-point gap that reflects two different trader pools reading the same underlying news rather than a meaningful disagreement about the likely outcome.
How do I trade the California billionaire tax market?
Sign up on Polymarket or Kalshi, fund your account, and buy "Yes" or "No" shares on the Prop 40 contract at the current market price. Shares can be sold back to the market at any time before the election, or held to resolution for a $1.00 payout if your side wins.
