Prediction markets posted their largest trading week on record, with cumulative volume reaching $20.4 billion, according to data from Artemis. It marks the first time weekly volume across the sector has exceeded the $20 billion threshold. The prior week came in just below that level at $19.8 billion. Both of the past two weeks have now surpassed the peaks recorded during the FIFA World Cup in June and July, which had stood as the sector's busiest stretch until this month. Prediction markets, broadly, are venues where traders buy and sell contracts whose payouts are tied to how real-world events resolve, from central bank decisions and crypto prices to elections and football games.

Daily figures also set records. Combined trading volume across prediction markets reached $4 billion on each of Saturday and Sunday this past weekend, with Kalshi accounting for roughly $3 billion on both days.

Kalshi Captures More Than Three-Quarters of Weekly Volume

Kalshi registered approximately 77% of all tracked volume for the week, at $15.8 billion. Polymarket ranked a distant second at $3.6 billion, followed by Nadex at $481.9 million and Rothera at $272.3 million, while Predict.fun and Opinion each cleared $120 million.

Polymarket nonetheless posted a strong weekend of its own, recording $770.4 million on Saturday and $662.4 million on Sunday. Kalshi's growth through September, however, has been considerably faster, and the gap between the two platforms now stands at its widest point of the year.

American Football Drives the Weekend Records

With September drawing to a close, the sector's trading volume for the month has already broken past the previous highs set in July. The records coincide with the start of the NFL and US college football season, and because most games are played on weekends, the bulk of sports-related trading has clustered in that window.

A substantial share of that activity flows through parlay-style combo contracts, which bundle multiple outcomes into a single bet. A trader might, for example, back three teams to win on the same Sunday afternoon. The contract pays out only if every leg hits, producing long odds and per-contract prices that often run to just a few cents.

Those low prices are where headline volume becomes inflated. Kalshi counts each contract at its $1 payout value rather than the amount the trader paid. A $20 bet on a long-shot parlay priced at 5 cents buys 400 contracts, which registers as $400 in volume. When thousands of such bets land on a busy football weekend, the dollar figures climb far faster than the money actually at risk. The effect is far smaller for contracts priced near $1, where the payout value is close to the amount paid — but with Kalshi representing roughly three-quarters of the week's volume, that counting convention plays an outsized role in the sector's headline figures.

Fed Decision, Crypto Markets and Midterms Added to the Total

Sports did not carry the entire week. The Federal Reserve's September rate decision drew steady positioning on both Kalshi and Polymarket. Short-duration crypto markets, which ask whether Bitcoin or Ether will close above a set price within hours or by the end of the day, turned over repeatedly as prices moved.

Traders have also begun positioning early for the Nov. 3 U.S. midterm elections, with control of both chambers of Congress at stake. Election contracts powered the sector's last major volume cycle in 2024, and the midterms are now five weeks away. The NFL regular season runs into early January.