Kalshi hits $60bn September volume as rivals erode market share
Kalshi posted $60 billion in notional September volume, a monthly record. Combo (parlay) contracts drove 85% of the notional growth but only 46% of taker gains. Rivals Polymarket US, DKeX, and Novig cut Kalshi's market share to around 80% during the same period. The data shows Kalshi expanding in absolute terms while ceding relative ground to a growing field of competitors. Combos accounted for most of the period-over-period growth.
Kalshi's combo dependence masks a structural vulnerability: parlays inflate headline notional while generating less than half the taker revenue of single-leg markets. Rivals Polymarket US, DKeX, and Novig are capturing the price-sensitive traders Kalshi is losing to margin compression. FanDuel's market-maker role inside Kalshi now looks like a holding pattern while the sportsbook fixes its own combo pricing.
Polymarket US weekly volume recently reached nearly $3 billion, proving it can scale without relying on sportsbook partners. The platform that delivers sharper combo odds by mid-NFL season will flip these share numbers, because liquidity follows pricing, not branding. Kalshi must close its pricing gap or watch a temporary volume lead become a permanent disadvantage.
Polymarket joins Kalshi in clearing multibillion-dollar monthly volumes, with both venues now competing for the same sports-driven trader base after their combined total hit $53 billion over the summer.