What is the wealth tax in California?
Prop 40 would impose a one-time 5% tax on billionaires' net worth, and prediction markets are pricing the California billionaire tax measure as a clear underdog heading into the Nov. 3 election.
Both Polymarket and Kalshi have the measure losing badly right now, with billionaire-backed opposition spending big to keep the California wealth tax from ever taking effect.
| 🏢 Platform | 🏷️ Pick | Price | 🤑 Est. Return on $100 | 📈 Trade It |
|---|---|---|---|
| Polymarket | Prop 40 | YES (30¢) | $333.33 | Trade it on Polymarket! |
| Polymarket | Prop 40 | NO (71¢) | $140.85 | Trade it on Polymarket! |
| Kalshi | Prop 40 | YES (26¢) | $384.62 | Trade it on Kalshi! |
| Kalshi | Prop 40 | NO (74¢) | $135.14 | Trade it on Kalshi! |
Below you'll find a full breakdown of the current Prop 40 odds across the exchanges, but if you want to jump straight in, check out the latest Polymarket promo code or the Kalshi promo code.
Right now, you can use the Polymarket promo code ACTION which will allow you to Deposit $10, Get a $25 Trading Bonus!
Prop 40 Polymarket Odds: Top Trading Contracts
Polymarket contracts trade from 1¢ to 99¢, mapping directly to implied probability on whether Prop 40 passes. A "Yes" contract settles at $1.00 if the measure is approved and $0 if it fails, and traders can buy or sell their position at any point before the market closes on Nov. 3, tracking the California wealth tax in real time as new polling and spending news breaks.
Prop 40 Passes (YES 30¢ / NO 71¢)
Polymarket traders have Prop 40 failing by a wide margin, and the one-point slip on the Yes side this week lines up with the billionaire-funded opposition campaign's ad blitz across the state.
Gov. Gavin Newsom and gubernatorial frontrunner Xavier Becerra have both come out against the California billionaire tax, giving the No side political cover even among Democrats who might otherwise back a tax on the ultra-wealthy.
Prop 40 Kalshi Odds: Top Trading Contracts
Kalshi lists Prop 40 as a single event contract that resolves based on California's official certified results from the Nov. 3 election, with the market itself closing early that morning. Pricing works the same way as Polymarket: cents equal implied percentage chance, and traders can enter or exit a position any time before close.
Prop 40 Passes (YES 26¢ / NO 74¢)
Kalshi is pricing Prop 40 even lower than Polymarket, with more than $1.5 million already traded on the contract. The sharper discount reflects just how skeptical traders have become that billionaire tax California backers can close the gap before Election Day.
Google co-founder Sergey Brin has personally put more than $100 million into the opposition campaign and its companion measures, and that spending edge shows up clearly in the Kalshi board.
You can sign up at Kalshi using promo code ACTION55 and you'll be able to Trade $25, Get $55!
How Polymarket and Kalshi Compare on the California Billionaire Tax
The two exchanges agree on direction: Prop 40 is losing on both boards, and neither market treats this as close. Polymarket has the Yes side at YES 30¢, while Kalshi has it four cents lower at YES 26¢, with the No side bid up to NO 71¢ on Polymarket and NO 74¢ on Kalshi.
That gap is modest but notable given Kalshi's deeper, more U.S.-concentrated trader base compared to Polymarket's broader international liquidity. The slightly steeper Kalshi price suggests its traders are weighting the opposition's record-setting ad spend a bit more heavily than Polymarket's crowd is.
Neither market is pricing in an upset. Both would need a meaningful swing in turnout or late undecided voters breaking hard for Yes to get Prop 40 back above even money.
California Billionaire Tax Price Analysis – Market Price Influencers
Prop 40 started the cycle with real momentum. An Institute of Governmental Studies poll in March had it near 52% support, and the Public Policy Institute of California still had it at 52% support as recently as September, even with countermeasures Prop 41 and Prop 42 also polling favorably.
But a separate September poll showed support sliding to just 37%, and campaign finance filings help explain why: opponents of the California wealth tax have outspent supporters by more than 5-to-1, with Brin-backed groups alone topping $100 million against roughly $36 million raised by the SEIU-UHW-led Yes campaign.
The market's shape right now is a clear underdog situation rather than a toss-up. Watch for any late PPIC or IGS poll in the final weeks, since both prediction markets have shown they'll move quickly on fresh survey data, and keep an eye on turnout among younger and more liberal voters, who poll as Prop 40's strongest base.
| 🏢 Platform | 🏷️ Pick | Price | 🤑 Est. Return on $100 | 📈 Trade It |
|---|---|---|---|
| Polymarket | Prop 40 | YES (30¢) | $333.33 | Trade it on Polymarket! |
| Polymarket | Prop 40 | NO (71¢) | $140.85 | Trade it on Polymarket! |
| Kalshi | Prop 40 | YES (26¢) | $384.62 | Trade it on Kalshi! |
| Kalshi | Prop 40 | NO (74¢) | $135.14 | Trade it on Kalshi! |
How to Trade the California Wealth 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 at kalshi.com/tc/55. 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: Final Thoughts
Both markets have the California billionaire tax losing, and the gap between the Yes and No sides has only grown as outside spending piled up against it. Watch turnout among younger, more liberal voters and any late-breaking poll for the one path back to a competitive race before Nov. 3.
Billionaire Tax California FAQs
What Is the Wealth Tax in California?
The wealth tax in California, known on the ballot as Proposition 40, is a one-time 5% tax on the net worth of state residents worth $1 billion or more as of Jan. 1, 2026. It targets roughly 200 billionaires statewide and would raise money largely earmarked for health care.
What Is the Wealth Tax in California Actually Funding?
Supporters say the tax is meant to offset federal cuts to Medi-Cal, with the bulk of revenue directed to health care programs and the remainder going toward education, food assistance, and administering the tax itself.
How Does Prop 40 Differ From Props 41 and 42?
Props 41 and 42 are billionaire-backed countermeasures, funded largely by Google co-founder Sergey Brin, designed to block new special taxes and bar retroactive taxation. If either one gets more "yes" votes than Prop 40, it would nullify the wealth tax even if Prop 40 itself passes.
Why Is Billionaire Tax California's Most Expensive Ballot Fight in 2026?
The billionaire tax California voters are deciding has drawn well over $200 million in combined campaign spending, with opponents alone outspending supporters by more than 5-to-1, making it one of the costliest ballot measure fights in state history.
How Do Polymarket and Kalshi Prices Differ on Prop 40?
Polymarket has the Yes side trading a few cents higher than Kalshi, 30¢ versus 26¢, though both exchanges agree the measure is more likely to fail than pass heading into Election Day.
When Does the Prop 40 Market Resolve?
Both markets resolve based on California's official certified results from the Nov. 3, 2026 general election.
Can You Trade Prop 40 Odds Right Now?
Yes, both Polymarket and Kalshi have active, liquid markets on Prop 40 that you can trade right up until the election, using the promo codes above to get started.
