Kalshi, Polymarket August Volume Drops 14.5% in First Monthly Decline in a Year

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Combined trading volume across prediction markets Kalshi, Polymarket and Polymarket US fell 14.5% in August from the previous month to $45.33 billion, ending a run of monthly increases that had lasted since August 2025.

Kalshi generated $37.17 billion in August volume, down 7.3% from $40.1 billion in July. Polymarket and its U.S. platform recorded a combined $8.16 billion, a 36.7% decline from $12.89 billion a month earlier, according to The Block’s data dashboard.

Prediction-Market Activity Retreats After World Cup Boost

The August pullback followed elevated summer trading, as the World Cup, held from June 11 through July 19, helped drive activity across prediction markets.

Still, trading remained well above pre-tournament levels. August’s combined volume of $45.33 billion was 76.7% higher than the $25.66 billion recorded in May.

The decline also comes as prediction-market operators face regulatory disputes in the United States over sports event contracts. More than a dozen states have pursued enforcement actions or litigation involving Kalshi and Polymarket.

Connecticut, for example, sued Kalshi last week seeking to stop the company from offering sports contracts, extending a legal dispute between the state and the prediction-market operator that has been running for months.

Kalshi Expands Sports Business Amid Regulatory Disputes

Despite the state-level challenges, Kalshi has continued expanding its presence in sports. The company recently reached a multi-year agreement with the U.S. Tennis Association to become the US Open’s exclusive prediction-market partner, with the partnership beginning with the 2026 tournament’s singles main draw on Aug. 30.

The agreement gives Kalshi a presence across US Open digital platforms and on-court signage while also establishing an integrity framework covering its tennis markets.

Kalshi has separately stepped up enforcement of its trading rules. Earlier this week, the company permanently barred former U.S. Representative George Santos from its platform, marking the first lifetime trading ban in Kalshi’s history.

The action stemmed from Santos’ trading in a contract tied to whether he would attend the State of the Union. Kalshi imposed a penalty of more than $71,000 and permanently prohibited him from trading on the platform.