# 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. - **Source:** [ReadWrite](https://brifing.si/source/7a996b61-bc09-4e57-8483-78f2ad9dd914) - **Published:** 2026-09-15 - **Topic:** [Finance](https://brifing.si/c/finance) - **Original article:** - **On Brifing:** https://brifing.si/s/bbf33159-9091-4e1e-9c5b-bd144d9cca4b ## Record-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. ## Sports 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. ## Six-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. ## Economic 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. ## Combo 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. ## Platform 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. ## Retail 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. ## Market 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. ## Sources covering this story - https://readwrite.com/prediction-market-volume-kalshi-lead/ — --- _Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._