Monthly trading volume on the prediction-market platforms Kalshi and Polymarket more than doubled from May to July, reaching $53 billion as sports contracts drove most of the increase, according to a Pew Research Center analysis.
The combined volume was $26 billion in May. Sports became the largest trading category on both platforms by a wide margin, Pew reported Wednesday, though its figures measure the notional value of contracts rather than the cash bettors or traders paid to acquire them.
Pew analyzed platform data from digital-assets information firm The Block covering July 2024 through July 2026. Kalshi and Polymarket are the two leading prediction markets in the analysis. The center said its earlier research found sports-focused users tend to place more trades than users focused on other topics.
Sports contracts dominate the increase
During June and July, when the FIFA World Cup took place, sports trading topped $58 billion on Kalshi and approached $22 billion on Polymarket, according to the analysis. Those are two-month totals, not the July monthly volume for either platform.
Pew compared legal U.S. sportsbook wagers of about $40 billion in the first quarter of 2026 with a roughly similar combined prediction-market sports volume during the same quarter. The measures are not identical: Pew counts each contract traded by a taker at its $1 payout value, regardless of the price paid for it. Some regulators have argued that sports event contracts amount to sports betting offered nationwide in conflict with state and local gambling rules.
A prediction-market contract resolves around a specified outcome. A contract trading at 40 cents, for example, implies a 40% chance under the market's pricing and pays $1 if the outcome occurs. Pew's volume calculation counts that trade as $1, not 40 cents.
Trading eased slightly in August but still totaled $47 billion across the two platforms, Pew said. Early September data suggested volume was rising again with the start of football season. Pew ended its detailed category analysis in July because of changes in the availability of data for certain Kalshi combination contracts.
The platforms have different trading mixes
Kalshi's growth accelerated more rapidly than Polymarket's. As recently as March, each platform accounted for about half the trading volume between them. By July, Kalshi had grown more sharply, Pew found.
Cryptocurrency became Kalshi's second-largest topic, with $6 billion in July trading, although that remained far below sports. Politics was comparatively small on both platforms in 2026. Monthly political volume averaged around $2 billion on Polymarket and stayed below $300 million on Kalshi, after politics led both platforms during the 2024 presidential election.
Polymarket's U.S. platform also took a larger share of its business. Pew said Polymarket US, launched in late 2025 as a federally regulated platform, rose from 4% of Polymarket's total volume in January to 39% in July. Pew's Polymarket figures include both its U.S. and international operations.
To compare topics, Pew regrouped categories reported by The Block across the platforms. For Polymarket's international platform, those categories rely on the first topical tag attached to a contract; Kalshi categories come from the platform, with certain combination contracts mapped where possible. Those choices and the July cutoff limit how precisely the topic trends can be compared beyond that month.
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