Short Answer

Both the model and the market expect a billionaire one-time wealth tax to pass in the California 2026 election, with no compelling evidence of mispricing.

1. Market Behavior & Drivers

The prediction market for a 2026 California one-time wealth tax has traded in a narrow, sideways range with a slight downward drift. The market opened pricing the initiative's passage at a 34.5% probability. It subsequently fell to 30.5%, where it has remained. This price action occurred after the measure, Proposition 40, officially qualified for the November 2026 general election ballot on June 17.
Market conviction is nonexistent. Total traded volume is zero, indicating that the price movement reflects automated adjustments rather than any trader activity. Without traded volume, conventional support and resistance levels are not established. The price range of 29.5% to 34.5% represents the bounds of the initial pricing mechanism. The current 30.5% price suggests sentiment is skeptical of the measure's passage, but this reading is entirely untested by market participants.
  • Yes appears supported by recent public polling showing majority voter sentiment.
  • Yes likely faces opposition from major business groups, impacting its prospects.
  • Yes is challenged by historical low success rates for similar tax initiatives.

Who Wins and Why

Outcome Market Model Why
Yes 30.0% 26.8% California voters may favor policies addressing wealth inequality and state revenue needs.

Current Context

California's Proposition 40, a wealth tax, qualified for the 2026 ballot. Proposition 40, officially titled "One-Time Wealth Tax for State-Funded Healthcare, Education, and Food Assistance Programs," qualified for the November 3, 2026, general election ballot on June 17, 2026 [1][2][3][4][5]. This measure proposes a one-time tax on certain individuals and trusts [3]. As of August 6, 2026, the election has not yet occurred, and voters have not yet decided the initiative [1][4][6].
The wealth tax faces ballot competition and political divisions. Proposition 40 is set against other tax-related initiatives, including constitutional amendments Proposition 41 and 42, designed to challenge its provisions [7][8][6]. Should multiple conflicting measures receive voter approval, the initiative with the most votes will prevail [7][8][6]. The California Democratic Party narrowly endorsed Proposition 40 in August 2026 [9]. Public discourse on wealth taxation includes arguments that the current system taxes wealth less than work [10], while some observers characterize the concept as "dumb crazy" [11].
Sources (11)
  1. 1California Proposition 40, One-Time Wealth Tax for State-...ballotpedia.org
  2. 2California proposal to tax billionaires makes November ballot | AP Newsapnews.com
  3. 3California Secretary of State Shirley N. Weber, Ph.D., Announces New Measure Eligible for November 2026 General Election Ballot. Imposes one-time tax on certain individuals and trusts. Initiative constitutional amendment and statute.:: California Secretary of Statesos.ca.gov
  4. 4California billionaire's tax qualifies for the Nov. 3 ballotnews.ballotpedia.org
  5. 5California billionaire's tax qualifies for the November ballotnews.ballotpedia.org
  6. 6Two California tax initiatives targeting personal asset taxes and special tax rules qualify for the ballot in challenge to billionaires’ tax initiative - Ballotpedia Newsnews.ballotpedia.org
  7. 7California billionaire tax heads to costly November ballot | Sacramento Beesacbee.com
  8. 8These are the ballot measures you’ll vote on in Novembercalmatters.org
  9. 92026 California Proposition 40en.wikipedia.org
  10. 10America’s Next President?: I’m WORRIED About America, Democracy Is On The Brink! | Pete Buttigiegyoutube.com
  11. 11Mark Cuban on the AI Bubble: Who Actually Gets Wiped Out?youtube.com

2. Price Chart

Historical Price (Probability)

Outcome probability
Date

3. Market Data

Contract Snapshot

Here are the contract rules for this market:

1. YES resolution: The market resolves to "Yes" if any statewide California proposition imposing a one-time tax on individuals, households, or family units with at least $1 billion (USD or equivalent) in wealth, assets, or net worth passes in the November 3, 2026 general election. 2. NO resolution: The market resolves to "No" if no such qualifying proposition passes. It will also resolve "No" if no qualifying ballot initiative is certified by the deadline, or if all qualifying propositions are removed or amended before the election such that the main threshold drops below $1 billion. 3. Key dates/deadlines: The relevant election is November 3, 2026. A critical deadline for a qualifying ballot initiative to be certified is June 25, 2026, 11:59 PM ET. 4. Special settlement conditions: The market will primarily use official information from the Government of the State of California for resolution. A consensus of credible reporting may also be used for settlement.

Available Contracts

Market options and current pricing

Outcome bucket Yes (price) No (price) Last trade probability
Yes $0.31 $0.70 30%

Market Discussion

Traders in this market generally anticipate that California's Proposition 40, a one-time billionaire wealth tax, will not pass in the 2026 election, reflected in its current 31% chance of success. Key arguments against its passage include strong opposition from Governor Newsom and other Democratic leaders, concerns about out-migration of high-net-worth residents, and competing "poison pill" initiatives designed to nullify the tax. Although earlier polling showed narrow support and one participant suggested the tax is "underpriced" due to potential voter irrationality, these points are largely overshadowed by the stated consensus favoring rejection.

4. Trust Index

Octagon Trust Index Polymarket 68 Caution

Settlement is decided by a token-holder vote.

Integrity risk· Outcome control

How it adds up
Integrity80% of score69Caution
Trade quality20% of score62Caution

Includes the cost to trade: a $10,000 order loses about 19% of the price to slippage.

Trust score68Caution

Weighted blend with hard caps — a critically weak safety pillar, or a severe trading anomaly, caps the total regardless of the rest. Full methodology · About the Trust Index

Trust profile
Integrity5 screens run · 4 don't apply · 1 awaiting data
Market integrity
65Caution

Outcome can be influenced

Outcome controlStructural risk · high confidence

Settlement is decided by a token-holder vote.

Screened clean
Participant influenceNo conflicted participant detected. Clear
Large tradesNo single trade dominates the tape. Clear
Thin-volume movesNo significant move Clear
Size patternsNo distribution read Clear
1 screen not run
Thin-leg conviction · doesn't apply to this market type
Info fairness
80Good

Structural prior — no screens apply

No suspicious activity on any screen

4 screens not run
Move vs. catalyst · doesn't apply to this market type
Longshot repricing · doesn't apply to this market type
Pre-broadcast certainty · doesn't apply to this market type
Cross-venue timing · data source not connected
Resolution quality
60Caution

Settlement depends on token voting

No suspicious activity on any screen

Resolution rules read: Clear

Settlement is decided by a token-holder vote.

Liquidity
74Tradeable

Fills fine at modest size

1 contract

Yes74
Tradeable · low confidence

Light recent trading — size may not fill near the screen price.

Move quality
70Stable

No significant moves

1 contract

Yes—
No significant move (24h)

Price was stable over the last 24 hours.

Rule clarity
100Clear

Counts toward Resolution quality, not here

1 contract

Yes100
Clear · high confidence

All checks pass

objective outcome · Clearofficial source · Cleartime boundary · Clear
Trade quality
62Caution

Tradable, but expect execution cost beyond small sizes.

Outcome quality 74 (notional-weighted)

$100 order: 0.6c slippage (~2% of a 28.5c contract)

$1,000 order: 1.4c slippage (~5% of a 28.5c contract)

$10,000 order: 5.5c slippage (~19% of a 28.5c contract)

Yes74Market scoreLiquidity74Move quality–Rule clarity100
Why 74
Liquidity
74 · Tradeable · low confidence

Light recent trading — size may not fill near the screen price.

Move quality
No significant move (24h)

Price was stable over the last 24 hours.

Rule clarity
100 · Clear · high confidence

All checks pass

objective outcome · Clearofficial source · Cleartime boundary · Clear

underwriting_v1.4 · computed Sep 20, 2026

5. How does the campaign messaging and funding for Proposition 40 compare to its competing measures, Propositions 41 and 42, ahead of the November 2026 election?

Prop 40 Tax RateOne-time 5% tax on assets over $1 billion [1][2][3][4]
Prop 40 BackerSEIU United Health Workers West [1][2][5]
Prop 41/42 Funding Source'Building a Better California,' funded by wealthy individuals including Sergey Brin [1][2][5][4][6][7][8]
Proposition 40 proposes a wealth tax to fund social programs. This citizen-initiated ballot measure aims to levy a one-time 5% tax on California residents possessing over $1 billion in assets [1][2][3][4]. The revenue generated from this tax is earmarked to support critical healthcare, food assistance, and education initiatives [1][2][3][4][9]. Notably, the labor union SEIU United Health Workers West is a primary backer of Proposition 40 [1][2][5].
Competing measures 41 and 42 aim to nullify new wealth taxes. Propositions 41 and 42 directly oppose Proposition 40, designed either to undercut or entirely invalidate its tax provisions [1][2][3][4]. Proposition 41 specifically suggests implementing constitutional amendments that would require state audits for new special taxes enacted after January 1, 2026 [1][2][3][6][8]. Meanwhile, Proposition 42 seeks to establish constitutional amendments prohibiting new taxes on retirement holdings and personal assets, alongside restricting retroactive taxation [1][2][3][7][8]. Both Propositions 41 and 42 receive significant financial backing from wealthy individuals, including Google co-founder Sergey Brin, channeled through the committee 'Building a Better California,' underscoring strong opposition to the proposed billionaire tax [1][2][5][4][6][7][8].
All three propositions qualified with a unique 'poison pill' feature. By June 2026, all three measures successfully qualified for the November 3, 2026, general election ballot [10][11][8]. A crucial element across these propositions is the inclusion of "poison pill" provisions, which dictate that should multiple measures pass, the one securing the highest number of votes will take precedence, potentially nullifying the others [1][3].
Sources (11)
  1. 1These are the ballot measures you’ll vote on in Novembercalmatters.org
  2. 2California’s final ballot: 14 measures for November | Sacramento Beesacbee.com
  3. 3Voter guide to Proposition 40: Billionaire taxcalmatters.org
  4. 4California Proposition 40, One-Time Wealth Tax for State-...ballotpedia.org
  5. 5California Democrats defy Newsom, back billionaire taxcalmatters.org
  6. 6California Proposition 41, Prohibit Excluding New State...ballotpedia.org
  7. 7California Proposition 42, Prohibit New Taxes on...ballotpedia.org
  8. 8Two California tax initiatives targeting personal asset taxes and special tax rules qualify for the ballot in challenge to billionaires’ tax initiative - Ballotpedia Newsnews.ballotpedia.org
  9. 9California 2026 ballot propositionsballotpedia.org
  10. 10California billionaire’s tax qualifies for the Nov. 3 ballot - Ballotpedia Newsnews.ballotpedia.org
  11. 11California billionaire's tax qualifies for the November ballotnews.ballotpedia.org

6. What is the historical success rate of progressive tax ballot initiatives in California over the past decade, and how do their campaigns compare to the current effort for Proposition 40?

Citizen-initiated measure success rate36% (since 1910) [1][2][3]
Legislatively referred measure success rate69% [1][2][3]
Proposition 40 proposed wealth tax5% (one-time on >$1 billion net worth) [4][5][6][7]
California citizen-initiated tax measures historically have a low success rate. Since 1910, approximately 36% of citizen-initiated ballot measures have been approved by voters, a notable contrast to the 69% success rate for legislatively referred measures [1][2][3]. Taxes frequently appear as subjects for California ballot measures [3][2]. While specific success rates for progressive tax initiatives over the past decade are not detailed in the research, California voters did reject Proposition 30, a progressive tax initiative, in 2022 [8].
Proposition 40, a wealth tax, faces significant opposition and complex challenges. This citizen-initiated measure, set for the November 2026 ballot, proposes a one-time 5% wealth tax on California residents with over $1 billion in net worth, intended to fund healthcare, education, and food assistance [4][5][6][7]. The initiative faces substantial hurdles, including strong opposition from Gov. Gavin Newsom and anticipated significant financial pushback [4][7][9][10]. Its prospects are further complicated by the qualification of two competing constitutional amendments for the 2026 ballot, which aim to potentially restrict or nullify such tax measures [4][7][9][10][11][12]. Although recent polling indicates slight majority statewide support, historical trends suggest that support often diminishes closer to an election, and intense opposition spending is expected [13].
Comparing Proposition 40's campaign to past initiatives lacks sufficient research data. The available research does not provide adequate details on the campaigns of other progressive tax initiatives over the past decade to allow for a direct comparison of their strategies or challenges with the current effort for Proposition 40.
Sources (13)
  1. 1How many initiatives have there been in California? - Ballotpediaballotpedia.org
  2. 2Californians decided on 1,306 ballot measures between 1910 and 2024 - Ballotpedia Newsnews.ballotpedia.org
  3. 3A comprehensive look at all ballot measures in California from 1910-2024 - Ballotpedia Newsnews.ballotpedia.org
  4. 4Voter guide to Proposition 40: Billionaire taxcalmatters.org
  5. 5Proposition 40 [Ballot]lao.ca.gov
  6. 6California Secretary of State Shirley N. Weber, Ph.D., Announces New Measure Eligible for November 2026 General Election Ballot. Imposes one-time tax on certain individuals and trusts. Initiative constitutional amendment and statute.:: California Secretary of Statesos.ca.gov
  7. 7California proposal to tax billionaires makes November ballot | AP Newsapnews.com
  8. 8California 2022 ballot propositions - Ballotpediaballotpedia.org
  9. 9California billionaire tax qualifies for November ballotcalmatters.org
  10. 10California billionaire’s tax qualifies for the November ballot; competing measures pending signature verification - Ballotpedia Newsnews.ballotpedia.org
  11. 11California billionaire’s tax qualifies for the Nov. 3 ballot - Ballotpedia Newsnews.ballotpedia.org
  12. 12Two California tax initiatives targeting personal asset taxes and special tax rules qualify for the ballot in challenge to billionaires’ tax initiative - Ballotpedia Newsnews.ballotpedia.org
  13. 13California voters weigh $100 billion wealth tax to offset Medicaid cutsmarketplace.org

7. What potential endorsements or opposition campaigns from major California business groups or public unions could significantly shift polling for Proposition 40 before November 2026?

Tax RateOne-time 5% on net worth exceeding $1 billion (2)(3) [1]
Early Voter Support50% (5) [1]
Competing AmendmentsTwo (Propositions 41 and 42) (2)(5)(6)(7) [1]
Proposition 40 proposes a significant wealth tax to fund public services. Sponsored by SEIU United Healthcare Workers West (UHW), this initiative suggests a one-time 5% tax on net worth exceeding $1 billion [2][3]. Funds generated would support state healthcare, food assistance, and education programs. Prominent supporters, including Senator Bernie Sanders and Representative Ro Khanna, advocate for the measure as a vital revenue tool for public services [1][2][4].
Opposition to Proposition 40 raises economic stability concerns. Governor Gavin Newsom and various business interests, such as the California Business Roundtable, are leading the campaign against the measure, joined by individual donors like Peter Thiel and Reid Hoffman [2][4]. These groups contend that Proposition 40 poses a risk to state economic stability and innovation, citing concerns about long-term fiscal impacts and a potential exodus of wealth from California [1][2]. While early polling indicates 50% voter support for the measure, many voters reportedly share anxieties regarding the economic consequences if wealthy individuals and businesses were to leave the state [5].
Competing ballot measures could challenge Proposition 40's efficacy. The landscape is further complicated by Propositions 41 and 42, two competing constitutional amendments that have also qualified for the November ballot [2][5][6][7]. These measures, sponsored by Building a Better California and funded by Google co-founder Sergey Brin, aim to challenge the billionaire tax. They do so by mandating audits and imposing constraints on future tax initiatives [2][5][6][7]. If Propositions 41 and 42 receive more votes than Proposition 40, they possess the potential to nullify it [2][5][6][7].
Sources (7)
  1. 12026 ballot measure pollsballotpedia.org
  2. 2Voter guide to Proposition 40: Billionaire taxcalmatters.org
  3. 3California Proposition 40, One-Time Wealth Tax for State-...ballotpedia.org
  4. 4California billionaire’s tax qualifies for the Nov. 3 ballot - Ballotpedia Newsnews.ballotpedia.org
  5. 5California billionaire tax qualifies for November ballotcalmatters.org
  6. 6California billionaire’s tax qualifies for the November ballot; competing measures pending signature verification - Ballotpedia Newsnews.ballotpedia.org
  7. 7Two California tax initiatives targeting personal asset taxes and special tax rules qualify for the ballot in challenge to billionaires’ tax initiative - Ballotpedia Newsnews.ballotpedia.org

8. What public polling data is available on California voter sentiment for Proposition 40, and which polling firms have been most accurate for past tax-related ballot measures?

Prop 40 Support (August 2026)Majority among likely voters [1]
PPIC Poll (May 2026)54% in favor [1][2][3]
Yes on Prop 40 Internal Poll (July 2026)57% support [1][4]
California's Proposition 40 shows majority support in recent public polling. This measure, proposing a one-time 5% tax on net worth exceeding $1 billion for state residents, has successfully qualified for the November 3, 2026, ballot [5][6][7][8][9]. As of August 2026, available public polling data indicates majority support among likely voters [1]. Specifically, the Public Policy Institute of California (PPIC) Statewide Survey in May 2026 reported 54% in favor, while the UC Berkeley IGS Poll, also from May 2026, showed 52% support [1][2][3]. An internal poll conducted by the 'Yes on Prop 40' campaign in July 2026 reported higher support at 57% [1][4]. Ballotpedia's indexing further reflects mixed public sentiment regarding Proposition 40 [10].
Historical accuracy data for polling firms on tax measures is limited. The Public Policy Institute of California (PPIC) is widely regarded as a reputable and nonpartisan firm frequently referenced for California ballot measures [11]. However, specific historical accuracy rankings for PPIC's projections on tax-related measures are not publicly quantified in its standard recent reports [11]. The available research does not provide information regarding the historical accuracy of other polling firms concerning tax-related ballot measures.
Sources (11)
  1. 1PPIC Statewide Survey: Californians and Their Government - Public Policy Institute of Californiappic.org
  2. 2Becerra, Hilton Lead Governor’s Race; Majority Back Billionaire Wealth Tax - Public Policy Institute of Californiappic.org
  3. 3UC Berkeleyescholarship.org
  4. 4New internal poll showing support for billionaire tax - KCRAkcra.com
  5. 5California Secretary of State Shirley N. Weber, Ph.D., Announces New Measure Eligible for November 2026 General Election Ballot. Imposes one-time tax on certain individuals and trusts. Initiative constitutional amendment and statute.:: California Secretary of Statesos.ca.gov
  6. 6California proposal to tax billionaires makes November ballot | AP Newsapnews.com
  7. 7California billionaire tax qualifies for November ballot | Sacramento Beesacbee.com
  8. 8It’s official: California voters will weigh a one-time billionaire taxsfchronicle.com
  9. 9California billionaire tax heads to costly November ballot | Sacramento Beesacbee.com
  10. 102026 ballot measure pollsballotpedia.org
  11. 11Will California's Billionaire Wealth Tax Pass in 2026?lines.com

9. What are the primary arguments from factions within the California Democratic Party who opposed the official endorsement of Proposition 40 in August 2026?

Prop 40 Tax Typeone-time 5% wealth tax on billionaires [1][2][3][4]
Withdrawal DeadlineJune 25, 2026 [5][6]
Opposition Descriptorstemporary, unreliable, and untested [1][2][3][4]
State leaders opposed Proposition 40, citing fiscal instability and economic harm. Key figures within the California Democratic Party, including Governor Gavin Newsom and gubernatorial candidate Xavier Becerra, opposed Proposition 40, arguing it represented a "temporary," "unreliable," and "untested" fiscal solution that could harm the state's budget, economy, and long-term prospects [1][2][3][4]. Governor Newsom and other state leaders reportedly engaged in negotiations with SEIU-UHW West, the measure's sponsor, attempting to persuade them to withdraw Proposition 40—a proposed one-time 5% wealth tax on billionaires—before its June 25, 2026, ballot qualification deadline [1][2][3][4][5][6].
Various groups raised concerns about economic impact and fiscal solutions. Labor organizations, such as the California Teachers Association, voiced apprehension that the proposed tax could lead to ultrawealthy residents relocating out of state, thereby reducing future tax revenue and complicating efforts to renew existing taxes that support schools [2][3][7][8]. Opposition from healthcare-related groups arose from a perceived lack of consultation during the measure's development, with critics contending that it would not address the fundamental structural or long-term fiscal challenges facing the healthcare system [3][7][8]. Further opposition from Democratic-aligned interests is evident through competing ballot initiatives, financed by individuals like Google co-founder Sergey Brin, designed to nullify or restrict the billionaire tax and other new special taxes [6].
Sources (8)
  1. 1California Democrats buck Newsom and union allies by endorsing populist billionaire taxcalmatters.org
  2. 2California Democratic Party endorses billionaire taxpolitico.com
  3. 3Billionaire tax measure wins backing of California Democratic Partysfchronicle.com
  4. 4California Democratic Party Endorses Billionaire Tax, Splitting with Newsom | KQEDkqed.org
  5. 5California billionaire’s tax qualifies for the Nov. 3 ballot - Ballotpedia Newsnews.ballotpedia.org
  6. 6Two California tax initiatives targeting personal asset taxes and special tax rules qualify for the ballot in challenge to billionaires’ tax initiative - Ballotpedia Newsnews.ballotpedia.org
  7. 7Voter guide to Proposition 40: Billionaire taxcalmatters.org
  8. 8California proposal to tax billionaires makes November ballot | AP Newsapnews.com

10. What Could Change the Odds

Key Catalysts

A one-time 5% wealth tax initiative, Proposition 40, has qualified for the California November 3, 2026, general election ballot [1][2][3][4]. The measure proposes a one-time 5% tax on the net worth of individuals and trusts with assets over $1 billion residing in California as of January 1, 2026 [5][6][7]. This initiative, which qualified on June 17, 2026, has not yet been voted on as of August 6, 2026 [6][8]. It aims to generate revenue for healthcare, education, and food assistance programs [2][3][9][5].
Competing measures, Proposition 41 (tax audits) and Proposition 42 (prohibiting new personal property taxes), have also qualified for the November 2026 ballot, doing so on June 24, 2026 [4][10][8]. These are intended to nullify or undercut the wealth tax if both pass, with the measure receiving more votes prevailing in such an event [4]. The SEIU-United Healthcare Workers West backs Proposition 40, while opponents include California Governor Gavin Newsom and various business groups [2][3][9]. Recent polling indicates voter division, with concerns regarding potential wealth flight and its impact on the state's long-term tax base [2][11][3].

Key Dates & Catalysts

  • Closes: November 03, 2026
Sources (11)
  1. 1California proposal to tax billionaires makes November ballot | AP Newsapnews.com
  2. 2California billionaire tax qualifies for November ballotcalmatters.org
  3. 3It’s official: California voters will weigh a one-time billionaire taxsfchronicle.com
  4. 4These are the ballot measures you’ll vote on in Novembercalmatters.org
  5. 5California Proposition 40, One-Time Wealth Tax for State-...ballotpedia.org
  6. 6California billionaire's tax qualifies for the Nov. 3 ballotnews.ballotpedia.org
  7. 7Signatures submitted for California initiative enacting one-...news.ballotpedia.org
  8. 8Two California tax initiatives targeting personal asset taxes and special tax rules qualify for the ballot in challenge to billionaires’ tax initiative - Ballotpedia Newsnews.ballotpedia.org
  9. 9California’s final ballot: 14 measures for November | Sacramento Beesacbee.com
  10. 10California billionaire's tax qualifies for the November ballotnews.ballotpedia.org
  11. 11California Wealth Tax Initiative 2026: Latest Pollsnytimes.com