Prediction markets went from 9% of legal US sports betting volume in January to 27% during the 2026 World Cup, according to H2 Gambling Capital, a threefold jump inside a single tournament.
The dollar totals behind that share are just as steep. Kalshi alone posted $31 billion in notional trading volume in June, up more than 70% from May, with sports contracts making up roughly 85% of that figure, according to Dune Analytics tracking of the exchange’s on-chain activity.
Users wagered close to $6 billion on the final alone across Kalshi and Polymarket combined.
A contract on either platform still works one simple way: buy at a price between 0 and 100 cents, and it settles at $1 if the event happens or nothing if it does not. What changed this tournament was how many people started trading that contract instead of placing a bet.
Statistics Trace Back to Two Different Rails
Kalshi settles in dollars as a CFTC regulated exchange, while Polymarket runs on the Polygon blockchain and settles trades in USDC, with no traditional clearinghouse between the two sides of a contract, part of a broader shift toward smart contract based settlement replacing multi-day clearing across finance generally, not just in prediction markets.
That structural gap shows up directly in pricing data. Polymarket carried the lowest average implied vig across the tournament at 2.70%, ahead of Kalshi at 4.71%, with DraftKings at 4.97%, FanDuel at 5.07%, BetMGM at 5.64% and Fanatics trailing at 6.14%.
That structural gap explains the pricing gap better than brand strength does, since a fee on a trade structurally leaves less margin than odds built to cover a sportsbook’s risk.
The World Cup Numbers Kept Climbing
The scale numbers kept climbing throughout the tournament. Kalshi’s market on the eventual champion alone generated over $1.2 billion in trading volume, the single largest market the platform has ever run, while the company added roughly 3 million new users during the World Cup.
App install data tells a comparable story. Prediction markets accounted for 27% of all World Cup bets by dollar volume, and Kalshi and Polymarket together captured 78.5% of betting app installs across six major platforms tracked through June, up from about 6% a year earlier, a swing that took roughly twelve months to complete.
Daily active users moved in opposite directions for the two categories. Kalshi’s daily users climbed 36% above its mid June level, while DraftKings fell 36% from its own tournament peak, FanDuel dropped 41%, and BetMGM and Caesars each slipped 32% across that stretch.
The Underlying Statistics Predate the Apps
None of this is as new as the World Cup coverage made it feel. Traders were doing this on a university server long before anybody built a phone app for it, and the research Iowa publishes on its own market is the reason people take the format seriously at all.
The Iowa Electronic Markets have run since 1988 with stakes capped at $500 to keep the project a study rather than a casino. Across five presidential elections the market price landed closer to the final result than the polls in about 74% of comparisons, and the gap was widest months out rather than on election eve.
Money is the enforcement mechanism behind that accuracy. A trader who talks nonsense on the internet pays nothing for being wrong, while a trader who buys a contract at 80 cents and watches it settle at zero has lost real money.
That gap filters out the loudest opinions fairly quickly, and sport was always going to be the next test case, since match outcomes settle fast, the data is public, and opinions on a final score are never in short supply. The World Cup handed that decades old format its biggest stage yet.
