Kalshi weekly volume hits $18.37B, more than double its level six weeks earlier

Kalshi recorded $18.37 billion in trading volume for Sept. 28–Oct. 4, 2026, up 17.28% from $15.66 billion in the preceding UTC week, according to defirate.com. That was the highest reading in the outlet’s seven-week comparison—not an independently established all-time record.

The latest total was more than twice the $9.06 billion reported for the week ending Aug. 23. Based on unrounded figures, the six-week increase was 102.65%. The expansion was concentrated: Kalshi’s identified Exotics category supplied 86.95% of the platform’s $2.71 billion weekly gain.

Multi-leg markets drive the increase

Exotics volume reached $11.82 billion, rising 24.87% from $9.47 billion and representing 64.34% of Kalshi activity. Leading individual markets included a 10-leg NFL combination of player statistics and team winners with $117.16 million in volume, and a 10-leg college football combination covering games and point spreads with $102.68 million. A four-leg MLB player-performance combination involving Matt Olson, Mookie Betts, Jonathan Aranda, and Manny Machado generated $36.19 million.

Those examples do not establish the sports composition of the entire Exotics category, according to defirate.com. Each combination’s volume is counted once at the parent-market level, not separately for each condition. Kalshi’s separately identified Sports category produced $3.64 billion, up 1.31%, while Football-tagged series reached $1.37 billion, up 7.20%. Soccer-tagged volume increased 40.73% to $452.63 million; Baseball-tagged volume dropped 32.59% to $362.07 million in the reporting week following the Sept. 27 end of the MLB regular season.

Growth extends beyond sports

Kalshi’s identified Crypto category rose 7.37% to $2.42 billion. BTC-tagged series accounted for $2.13 billion, up 6.78%, including BTC-versus-ETH products; ETH-tagged series reached $118.90 million, up 21.61%. These tags can overlap and therefore cannot be summed. Financials increased 646.26% from $11.16 million to $83.25 million—a sharp percentage rise from a much smaller base than Exotics, Sports or Crypto.

Commodities volume climbed 24.38% to $274.64 million. Among smaller identified categories, Science and Technology increased 51.30% to $6.93 million, Economics rose 47.16% to $19.34 million, and Mentions advanced 31.34% to $9.80 million. The report treats Financials, Economics and Commodities separately rather than combining them into a single finance measure.

Polymarket readings diverge

Polymarket US volume declined 4.41% to $2.71 billion for Sept. 28–Oct. 4 Business Dates, from $2.83 billion for Sept. 21–27, according to defirate.com. The pullback followed a 223.22% increase, calculated using unrounded values, from a retained late-August benchmark of $876.42 million to the Sept. 21–27 total. Separately, Polymarket’s Eastern-calendar dollar volume increased 6.26% to $519.01 million from $488.42 million.

The platform figures are not directly interchangeable. Kalshi and Polymarket US use a $1 face-value volume convention, not cash spent, while Polymarket measures volume at execution prices. Their reporting calendars also differ: UTC weeks for Kalshi, official Business Dates for Polymarket US and Eastern-calendar weeks for Polymarket. The period spans the Sept. 30 end of Q3 and Oct. 1 start of Q4, but measures completed weeks rather than quarterly performance.

What it means for prediction markets

• The central question is persistence. Subsequent completed UTC weeks will show whether Kalshi maintains its $18.37 billion level after six weeks of substantial expansion.
• Market composition matters. Exotics contributed 64.34% of Kalshi volume and most of its weekly increase. The headline growth rate should not be read as uniform expansion across categories.
• Cross-platform totals require caution. Different valuation conventions and reporting calendars prevent these three figures from being combined into a consistent industry total.
• Volume is not evidence of trader migration. The category comparison uses a fixed mapping of identified series, with overlapping tags and some unclassified volume. Gains in Crypto and Financials do not establish that participants shifted away from sports.