The combined trading volume across Kalshi, Polymarket, and Polymarket US fell 14.5% in August to $45.33 B. According to data from The Block’s dashboard, this was the first monthly decline since August 2025.
Kalshi recorded $37.17 B in trading volume, down from $40.1 B in July, a 7.3% decline. Polymarket and Polymarket US saw their combined trading volume fall 36.7%, from $12.89 B to $8.16 B.
Pullback After the World Cup
The July peak came as the World Cup drew to a close. Kalshi’s market on the Spain–Argentina final generated around $1.9 B in trading volume, while the Polymarket contract generated around $4 B.
After the tournament ended, activity in sports markets declined, leading to the first monthly drop in a year. Even so, August trading volume remained well above the May figure of $25.66 B.
Sports continue to be Kalshi’s largest segment. In the week of August 24–30, trading volume on its contracts exceeded $10 B for the first time, reaching $10.17 B.
Legal Pressure on the Sector
Kalshi and Polymarket are also facing growing pressure from U.S. authorities over sports contracts. More than a dozen states have already begun enforcement actions or filed lawsuits.
On August 26, Connecticut Attorney General William Tong filed a lawsuit against Kalshi, seeking to ban the platform from offering sports contracts to state residents. Authorities consider these contracts to be unlicensed sports betting.
On August 31, Kalshi issued its first-ever lifetime ban to former Congressman George Santos and fined him $71,356. According to the platform, Santos traded a contract tied to his own appearance in the U.S. president’s address to Congress and made public statements that could have influenced the contract’s price.
We previously covered regulators’ efforts to crack down on insider trading in prediction markets here, here, and here.
Markets Await the Next Sports Peak
The next major source of sports trading volume will be the NFL season, which begins on September 9 with a game between the New England Patriots and the Seattle Seahawks. Both platforms already offer contracts for the first week of the season as well as season-long futures.
Kalshi has also reached an agreement with the United States Tennis Association (USTA) and become the exclusive prediction-market partner of the US Open.