Kalshi Dominates Prediction Markets with 92.1% Share as Weekly Volume Hits $14.1B
Sports and economic events drive record trading activity across decentralized platforms.
1Record-breaking trading volume
Kalshi and Polymarket Global reached $14.10 billion in contract volume during September 7-13, marking a 9.3% increase from the previous week. This surge coincided with the NFL season opening, US Open tennis, esports playoffs, and Federal Reserve positioning. Kalshi accounted for $12.98 billion (92.1% share) of this volume, setting a platform record. The combined trade count rose 10.7% to 86.50 million contracts, demonstrating growing retail participation in prediction markets.
2Sports dominate retail activity
Sports contracts generated $3.76 billion in trading volume across both platforms, representing the largest retail activity segment. Kalshi processed $3.265 billion in sports contracts, while Polymarket Global saw a 104.7% jump to $498.81 million. High-volume NFL markets included New England-Seattle ($57.86 million), San Francisco-Los Angeles ($45.30 million), and Washington-Philadelphia ($28.48 million). The data reveals sports betting as the primary driver of prediction market growth during major league openings.
3Six-week growth streak
The reported week capped a six-week period of continuous growth from August 9 through September 13. Kalshi's weekly volume increased 60.9% from $8.069 billion to $12.983 billion during this period. September's month-to-date volume through September 13 reached $23.45 billion, 53.4% higher than the same August period. This sustained growth trajectory indicates expanding mainstream adoption of decentralized prediction platforms beyond traditional financial instruments.
4Economic event trading surges
Beyond sports, Polymarket Global's Fed Decision market generated $48.85 million, up 48.8% from the previous week. This reflects growing trader interest in using prediction markets for macroeconomic speculation. Meanwhile, four League of Legends playoff matches combined for over $38.74 million in volume, highlighting esports' emerging role in prediction markets. The data shows diversification beyond traditional sports into economic and gaming verticals.
5Combo contracts dominate
Kalshi's multi-leg combo contracts, allowing traders to bundle predictions, reached $1.93 billion in volume - representing 99.4% of the $1.95 billion combo market across both platforms. This product innovation appears central to Kalshi's dominance, offering sophisticated traders more complex position-building capabilities. Open interest stood at 677.18 million contracts on Kalshi as of September 13, significantly higher than Polymarket's 321.34 million (Global) and 164.19 million (US) figures.
6Platform differentiation
While Kalshi maintained overall volume dominance, Polymarket Global recorded gains in sports trading and Fed decision activity. The data reveals distinct platform strengths - Kalshi leads in combo products and total volume, while Polymarket shows stronger week-over-week growth in specific event categories. This suggests market segmentation may be developing, with traders selecting platforms based on specific contract types or event coverage.
7Retail participation metrics
The $14.10 billion weekly volume across 86.50 million trades implies an average contract size of approximately $163, indicating significant retail rather than institutional participation. Sports contracts averaged about $44 each across platforms, while economic event contracts showed higher average values. These metrics suggest prediction markets are primarily serving individual traders rather than large financial entities at current adoption levels.
8Market maturity indicators
The sustained six-week growth, product diversification (sports, economics, esports), and platform specialization (combo contracts vs. event trading) collectively suggest prediction markets are maturing beyond novelty status. Kalshi's 92.1% share indicates potential winner-take-all dynamics, though Polymarket's niche strengths in specific verticals may sustain competition. The data paints a picture of an evolving alternative trading ecosystem parallel to traditional financial markets.