Prediction Market Statistics

Volume is the price multiplied by the number of contracts for each trade, counting only one side, summed into weekly totals.

Notional volume is the number of contracts traded, counting only one side of each trade, summed into weekly totals.

Open interest is the number of dollars in active markets for a given venue.

No venue publishes a fee column, so fees are estimates. We apply each venue’s published fee schedule to every trade, using the rates in effect on the trade date, and include both the taker and the maker fee where a schedule charges both. When we are unsure, we understate, and anything the files cannot identify, such as a trader’s volume tier, is left out. Treat these figures as a floor.

Kalshi pays a taker fee of 7% times contracts times price times (1 - price), and 3.5% on index contracts. Maker fees are not modelled.

Polymarket US charges takers 0.06 times contracts times price times (1 - price), and 0.0695 from 2026-09-17. Makers receive a rebate and no fee. Table tennis and combo formulas are not modelled.

Novig charges only the taker side: 0.10 on combos and 0.06 on NFL, MLB and NCAAF futures. Straights are charged only while the event is live, and the files carry no in-game flag, so straights are treated as free.

Gemini charges a taker fee of 0.07 and a maker fee of 0.0175, rounded up to the cent, on listings from 2026-03-18. Maker fees are waived from 2026-09-02 to 2026-12-31, and nothing is counted before 2026-03-18.

UnderdogX has changed its fee schedule many times since launch. We apply the current one to every date: takers 0.07 and makers 0.0175, rounded to the cent. Combos have paid a 0.07 maker fee since 2026-10-09 and none before. Earlier schedules charged makers more in places, so the earlier figures may understate.

Rothera charges 0.02 per side, which is the retail rate. The files show no participant type, so professional and market-maker rates cannot be told apart.

Crypto.com charges $0.02, $0.10 or $1.00 per side per contract, depending on whether it is a $1, $10 or $100 contract. We read the size from the price scale, so a $10 contract trading under $1 is counted as a $1 contract.

ForecastEx charges $0.01 per contract on each side, Yes and No, of every matched pair. Its block trades are fee-free from 2026-09-22 to 2026-12-01, but the files do not mark them, so we charge them too. ProphetX is charged only on parlays, from 2026-08-19. We assume no fee on straights: they pay 2% of each customer’s net gains at settlement, which cannot be worked out from trades, so this figure understates ProphetX.

Railbird charges takers $0.01 per contract on every trade, combos included, and makers $0.0025, each rounded up to the cent. From 2026-10-01 the maker fee on combos is 0.035 times price times (1 - price) instead. The files do not say which side was the taker, so we use the printed price.

Polymarket is not an estimate: it is the USDC fee recorded on-chain for each fill. Refunds paid back to traders are not subtracted, so this figure can run slightly high.

PredictStreet is not included. Part of its fees are paid in outcome shares rather than USDC.

Transactions are the number of trades in each week, counting only one side of each trade.

Users are the number of unique traders in each week. A week or month counts each trader once, so it is not the sum of its days.

Volume is the price multiplied by the number of contracts for each trade, counting only one side. Trades across every venue, split by the topic of each market. Every series of markets on a venue carries exactly one topic, so no trade is counted twice. Combos (parlays) are their own series. Untagged is trading in markets not tagged with a topic yet: new market series before the next tagging run, and trades a venue files without a market.