Prediction Markets Post $50.6 Billion July Volume as Open Interest Falls

Overview

• Data published on Aug. 3 show combined monthly notional trading volume across Kalshi, Polymarket and Polymarket US reached about $50.59 billion in July, driven largely by World Cup contracts.
• Kalshi supplied roughly $37.7 billion of that volume while Polymarket US rose about 54% to near $5 billion, making the three-platform total a record.
• Open interest fell sharply after the World Cup as many event contracts settled, dropping from about $2 billion earlier in July to roughly $1.2 billion by month-end, which signals less capital committed after settlement.
• Market structure shifted: Kalshi retained the most listings and the largest share of remaining open positions, Polymarket increased its share of open interest and led short-term daily turnover, and smaller venues lost capital faster.
• The reported $50.6 billion measures taker notional turnover rather than customer deposits or platform revenue, and the sector now faces a test in August to see if non-sports markets and the outcome of New York and Minnesota court actions sustain activity and user access.