Kalshi and Polymarket's combined volume falls 15% in August, first monthly decline in a year

Kalshi and Polymarket saw their combined volume decline last month, the first month-over-month drop in a year, following a World Cup-driven surge.

According to The Block's data dashboard, the combined monthly volume at Kalshi, Polymarket and Polymarket US fell 14.5% in August to $45.33 billion, marking the first decline since August 2025.

Specifically, Kalshi recorded $37.17 billion in volume in August, down 7.3% from $40.1 billion in July, while Polymarket and its U.S. platform saw a combined $8.16 billion, down 36.7% from $12.89 billion in July.

The August pullback followed a summer spike in prediction market activity driven by the World Cup, which ran from June 11 to July 19. Still, the August volume remained well above May's $25.66 billion.

Meanwhile, both Kalshi and Polymarket are facing increased scrutiny from state regulators in the U.S., particularly over sports-related contracts. Over a dozen states have taken enforcement action or filed lawsuits against Kalshi and Polymarket.

Last week, Connecticut sued Kalshi to block the platform from offering sports contracts, escalating the state's months-long legal fight against the platform.

Despite escalating legal fights with state-level authorities, Kalshi is still expanding its footprint in sports.

It recently signed a deal with the U.S. Tennis Association to become the exclusive prediction market partner of the U.S. Open, whose main draw began Aug. 30.

Meanwhile, earlier this week, Kalshi permanently banned former U.S. Rep. George Santos from trading on the platform, marking its first-ever permanent ban. Santos violated its rules by trading a bet on whether he would attend the State of the Union, and was ordered to pay a fine of over $71,000.