How US Midterm Election Betting Became a $220 Million Market
The market for betting on US midterm elections is expanding rapidly, turning political outcomes into tradable financial contracts. Platforms such as Polymarket and Kalshi are attracting traders who want to speculate on which party will control Congress, how closely individual races will be contested and whether candidates will withdraw before voting.
According to research by the Anti-Corruption Data Collective (ACDC), more than $220 million in bets had been placed on the 2026 US congressional midterms by September 30, compared with $92 million across the entire 2024 congressional election cycle. The research covered more than 21,000 markets across Kalshi and Polymarket’s US and international platforms.
The growth reflects a broader shift in how people use digital platforms to express views about political and economic events. Rather than simply reading polls or following campaign coverage, participants can now put money behind their expectations.
However, rising trading activity does not automatically mean these markets provide reliable forecasts. Concentrated trading, potential manipulation and access to confidential information remain significant concerns.
How Election Prediction Markets Work
Prediction markets allow participants to buy and sell contracts tied to the outcome of a specific event. A contract might ask whether a particular candidate will win a Senate race or whether Democrats will control the House of Representatives after the election.
In a simple binary market, a contract pays a fixed amount if the stated outcome occurs and nothing if it does not. Its trading price can be interpreted as an implied probability, although that interpretation is affected by trading costs, liquidity and market structure.
For example, if a contract that pays $1 when a candidate wins trades at $0.60, the price can be read as an implied 60% probability. It does not mean the candidate has a scientifically established 60% chance of winning.
As new polls, campaign developments and economic data emerge, traders may buy or sell contracts, changing their prices.
The platforms argue that this process can aggregate information from many participants. Supporters believe that people risking their own money have an incentive to assess events carefully rather than simply express a political preference.
Critics counter that prices can be distorted when a small number of traders dominate activity or when reliable information is scarce.
What the 2026 Trading Data Reveals
The ACDC research found that election betting has become more detailed than it was during the 2024 congressional cycle.
Indicator | 2024 cycle | 2026 cycle |
|---|---|---|
Reported betting volume | $92 million | More than $220 million by September 30 |
Markets focused on race winners | 71% | 16% |
Markets focused on winning margins | — | 58% |
Figures reflect ACDC's analysis of congressional election markets. The 2026 total was measured through September 30, rather than the end of the election cycle.
The shift toward winning margins shows that platforms are offering increasingly granular questions. Traders are not just wagering on who wins; they are also speculating on how large a victory might be and how voters will participate.
But the total volume needs context. Although more than $220 million has been wagered, the activity is concentrated in a relatively small number of races. The Texas Senate contest involving Democrat James Talarico and Republican Ken Paxton was a major focus, alongside races in Maine, Michigan and South Carolina.
ACDC also found that the top 1% of wallets on Polymarket's international platform, ranked by trading volume in congressional markets, accounted for 70% of congressional election betting volume in this cycle.
That concentration matters because a large trading volume does not necessarily represent a broad consensus among voters. A small group of heavily active traders can account for a disproportionate share of transactions.
The Insider-Trading and Election-Integrity Problem
The rapid expansion of election prediction markets has raised questions about who is allowed to trade and what information they can use.
Candidates, campaign staff and political insiders may have access to information unavailable to ordinary participants. If they use confidential knowledge to place bets, they could gain an unfair advantage and undermine confidence in the market.
Reuters reported that Kalshi had suspended candidates for betting on their own races. Public broadcaster NPR also reported in May that campaign staffers had been betting on races they worked on.
The concern extends beyond financial fairness. If confidential information about political decisions or government actions can be reflected in trades before the public learns about it, markets may create incentives to exploit privileged access.
There is also a risk of manipulation. If a market has limited liquidity, relatively small trades can move its displayed odds. Those movements may then be interpreted by observers as evidence of changing political momentum, even when the underlying voter preferences have not changed.
The industry disputes the suggestion that its markets are inherently unreliable. Polymarket says it uses surveillance and detection systems, while platforms argue that trading prices can offer useful information that complements traditional polling.
Neither position removes the need for independent oversight and transparent rules.
Public Opposition Is a Major Challenge
The industry's growth has not translated into broad public approval.
A Reuters/Ipsos poll conducted from September 30 to October 5, 2026, found that 69% of Democrats and 61% of Republicans opposed using prediction markets to bet on election results. The survey included 4,506 US adults and had a margin of error of approximately two percentage points.
The same poll found that 65% opposed betting on US military actions and 63% opposed wagering on government policy announcements or decisions. Three-quarters of respondents considered prediction markets on real-world events a form of gambling.
This creates a difficult environment for operators. They are trying to build a market that resembles a financial exchange, while many consumers and policymakers view at least some of its contracts as gambling on events with wider social consequences.
The distinction is especially sensitive when contracts relate to elections, military operations or government decisions rather than conventional financial assets.
Regulation Could Determine the Industry's Future
Regulatory uncertainty is one of the biggest risks facing prediction-market operators.
At the centre of the debate is whether these contracts should primarily be treated as financial instruments overseen by the federal Commodity Futures Trading Commission (CFTC), or as gambling products subject to state-level rules.
The Trump administration has supported developing a federal framework for the industry, while state regulators have challenged the view that federal oversight should take precedence. The dispute could shape which markets platforms can offer, who can participate and how misconduct is investigated.
For businesses operating these platforms, stricter rules could increase compliance costs and limit certain products. Clearer regulation could also give participants greater confidence in market integrity, although the effect on trading volumes is uncertain.
Investors and industry observers should watch for regulatory decisions, restrictions on political insiders, enforcement actions and changes to the range of contracts available.
What the Election Betting Boom Means for Investors
Prediction markets sit at the intersection of financial technology, political forecasting and online speculation. Their growth could create opportunities for companies providing trading infrastructure, data analytics and market surveillance, but the commercial benefits will depend on regulation and sustained user demand.
There are also important limitations for anyone using these markets as an information source.
Implied odds are not polling results. They reflect contract prices, not a representative survey of voters.
Trading volume can be concentrated. A large market total does not necessarily indicate broad participation.
Prices can move without a fundamental shift. Low liquidity and large trades may change displayed probabilities.
Regulation can change quickly. Restrictions could affect platform access and business models.
Forecasts can be wrong. Even active markets with substantial participation cannot eliminate uncertainty.
For investors, the most useful approach is to treat prediction-market prices as one source of information rather than a definitive guide to election outcomes or future policy.
Political results can influence taxes, regulation, government spending, energy policy and the outlook for industries such as banking and technology. But turning a market's odds into an investment decision requires further analysis of the actual policies at stake and the extent to which asset prices already reflect expectations.
Conclusion
The US midterm election betting market has expanded sharply, with reported volume exceeding $220 million by September 30, 2026. More detailed contracts, concentrated trading and growing interest in political outcomes have helped drive the expansion, while concerns over insider trading, manipulation and public trust remain unresolved.
The industry's next phase will depend not only on the accuracy of its forecasts but also on whether platforms can demonstrate fair trading practices and operate within a clear regulatory framework. Investors should distinguish market-implied probabilities from verified political facts and independently assess the economic consequences of election outcomes.
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Disclaimer: This article is for informational and educational purposes only and should not be considered investment advice.