Prediction markets recorded a monthly record $75.5 billion in notional volume in September, as sports, crypto and multi-event combination contracts—not political bets—drove activity ahead of the US midterm elections. Those three categories made up 94% of the total, while political contracts generated $901 million. The figures point to trading activity extending beyond the election cycle, but notional volume is shaped by how contracts are priced and does not equal the cash users put in.
NFL season lifts activity in short-dated contracts
The figures cover Kalshi, Polymarket’s international and US markets, and Novig. September’s record coincided with the start of the NFL and college football seasons, giving sports contracts a steady schedule of events. Unlike political contracts that may take months to settle, sports markets turn over quickly, allowing traders to commit funds again after one event resolves.
Crypto contracts can also have short time frames. Kalshi, for example, offers contracts that settle on whether a cryptocurrency’s price rises or falls over a 15-minute window. These markets track continuous price movements, allowing for repeated rounds of trading and settlement without waiting for an election or another distant event.
Multi-event combination contracts bundle several outcomes into one position, much like a parlay in sports betting; some are priced at just a few cents. Kalshi offers these contracts across sports and other event categories, so combination-contract volume cannot all be classified as sports trading. Their broad scope also makes it difficult to assess each event category’s contribution to a platform’s business from contract labels or aggregate volume alone.
Cheap combination contracts amplify notional volume
The way notional volume is calculated is central to understanding the record. If a contract can pay out up to $1, a trade may count as $1 in notional volume even when the buyer paid only a few cents. Low-priced contracts can therefore produce large headline trading figures despite relatively modest purchase outlays.
Kalshi’s combination contracts alone accounted for $34.2 billion in notional volume in September. As trading in low-priced combinations increased, the platform’s notional volume grew relative to the amount buyers spent. The report found that the average purchase price for Kalshi contracts with a maximum payout of $1 fell from 32 cents in July to 24 cents in September, attributing the decline to a larger share of combination contracts. Polymarket’s average purchase price held at about 50 cents over the same period.
At a lower average contract price, the same dollar of spending can correspond to more notional volume measured against maximum payouts. Notional volume can track contract activity, but it is not the same as funds received by a platform, user spending or platform revenue.
Kalshi gains notional share as political trading remains concentrated
Kalshi’s share of notional volume rose from 69% in July to 73% in both August and September. Novig’s data were included only from August 4, however, so the change in coverage should be considered when comparing platform shares across months.
Political contracts made up a relatively small share of industry-wide trading in September, but remained significant on some platforms. Polymarket’s US market handled more than half of political-contract trading that month. Political activity continued alongside high volumes in sports, crypto and other event markets, with category mixes varying by platform.
Across the four platforms, sports, crypto and combination contracts together accounted for 94% of September’s $75.5 billion in notional volume. The record came before the final stretch of the US midterm election campaign, indicating it was not driven solely by a surge in election trading. The low purchase prices of combination contracts also meant the headline notional total substantially exceeded the spending those trades represented.