Kalshi, Polymarket and Polymarket US reported a combined $50.59 billion in trading volume for July, a monthly record driven largely by FIFA World Cup contracts. The total rose 7.8% from $46.95 billion in June, even as open interest across the three venues fell sharply after the tournament ended, indicating that much of the activity was tied to short-lived sports events rather than longer-running positions.
Kalshi accounted for the largest share of July trading, reporting $37.7 billion in volume, up 14% from June. Polymarket recorded $7.9 billion, down 26% month over month, while Polymarket US posted the fastest growth, with volume rising 54% to $5 billion.
The figures place Kalshi at the center of the World Cup trading surge and show a diverging picture for the two Polymarket operations. Polymarket US gained activity after lifting its initial waitlist restrictions in May, opening the service to all U.S. users. Yet that expansion did not fully offset the drop on Polymarket’s main platform, where monthly volume declined.
World Cup contracts powered July turnover
The FIFA World Cup ran from June 11 through July 19, concentrating global attention on a sequence of matches, team outcomes and tournament-wide predictions. Those events produced some of the largest individual contracts on the platforms during the month.
Kalshi’s market tied to the final between Spain and Argentina drew roughly $1.9 billion in trading volume, according to the platform’s figures. Polymarket’s contract on the eventual tournament winner attracted about $4 billion. The two contracts alone accounted for nearly $6 billion in trading, demonstrating how a single major sporting event can concentrate liquidity in prediction markets.
Prediction-market contracts allow users to trade on whether a defined event will occur, with the contract generally settling at a fixed value if the outcome is correct and at zero if it is not. During a tournament such as the World Cup, contracts can be created around every stage of the competition, from a team’s progress to the result of a particular match. The rapid arrival of fresh information — team selections, injuries, match results and elimination rounds — can generate sustained trading through the event’s final weeks.
Kalshi’s July increase suggests it captured a larger portion of that demand than its rivals. Its $37.7 billion monthly total represented almost three-quarters of the three-platform aggregate, compared with Polymarket’s combined $12.9 billion across its offshore and U.S. operations.
Polymarket’s U.S. growth did not reverse the combined decline
Polymarket US reported $5 billion in July volume, up from roughly $3.25 billion in June based on the stated 54% monthly increase. The platform’s removal of waitlist limits in May gave it access to a wider pool of U.S. users during one of the year’s biggest sports betting and prediction-market events.
The main Polymarket platform moved in the other direction. Its $7.9 billion in July volume was 26% below June’s level, according to the reported platform figures. Across the two Polymarket venues, volume fell from $14 billion in June to $12.9 billion in July.
That split complicates any simple reading of U.S. access as a direct transfer of activity from the main platform to Polymarket US. The World Cup itself created unusually high demand across the sector, while the different platforms were competing for contracts, liquidity and users during a brief, high-volume period.
Harry Crane, a statistician at Rutgers University, estimated that U.S. users represented about 30% of volume on Polymarket’s main platform during the 12 months ending April 30, 2026. His estimate included users who had used workarounds to access the offshore venue. The figure points to the scale of U.S. demand that had previously reached Polymarket’s international platform despite its formal restrictions.
Open interest fell after the final
The July volume record was accompanied by a decline in open interest once the World Cup concluded. Open interest across Kalshi, Polymarket and Polymarket US fell from about $2 billion at the beginning of July to $1.2 billion by the end of the month, according to the reported platform data.
Open interest measures the value tied up in contracts that remain unresolved. Its decline after July 19 reflects the settlement of contracts linked to the final and other tournament outcomes. Trading volume can remain high during a major event because users repeatedly buy and sell contracts, while open interest falls once the event that underpins those trades reaches a definitive result.
The $800 million reduction also shows that the record monthly turnover did not translate into a permanently larger base of outstanding positions. Sports events can draw large amounts of short-term activity, but their contracts tend to close quickly once results are known.
State disputes remain a constraint on sports contracts
The surge in World Cup trading came as Kalshi and Polymarket continued to face legal challenges in the United States over sports-linked event contracts. More than a dozen state regulators have accused the platforms of offering unlicensed gambling products and have sought to stop such contracts in their states, according to the supplied account of the disputes.
Kalshi and Polymarket, alongside the Commodity Futures Trading Commission, have challenged those state actions. Their position centers on federal preemption: the argument that federally supervised event-contract markets fall under the CFTC’s authority rather than separate state gambling laws.
The outcome carries practical consequences for platforms trying to build regulated U.S. prediction markets around sports. A favorable federal interpretation would give venues more room to list contracts linked to games, tournaments and awards. State regulators, meanwhile, argue that sports-related contracts can fall within gambling rules designed to protect consumers and preserve local control over betting.
July’s numbers show the commercial appeal of sports markets while also exposing their dependence on a small number of major events. Kalshi’s record-setting month, Polymarket US’s rapid growth and the post-tournament decline in open interest leave the legal fight as the next major factor shaping how long that activity can persist in the U.S.
Explore how event contracts work in practice with Toobit’s detailed guide on event contracts and prediction-style trading.
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