Jeremy BraginStart here
Three guides, in the order they make sense. The first explains the idea; the next two show it on the two biggest apps.
The idea · 7 min
What are prediction markets?
How a $1 contract works, why its price is a probability, how accurate markets are and who regulates them.
One app · 7 min
How does Kalshi work?
One trade from price to payout, with the real fee, order types, settlement and what can go wrong.
One app · 7 min
How does Polymarket work?
Polymarket US and the international site, how each settles, and what each charges.
What trading costs
Fees vary more than prices do, and most follow the same curve: highest at 50¢. These pages do the arithmetic.
Is it legal where you are?
Prediction markets are federally regulated in the US, and contested in several states. Outside the US, each app keeps its own list.
Choosing an app
More than a dozen regulated apps now offer event contracts. We score them on the same six criteria and compare them head to head.
How we work
How we match the same question across venues and how we score apps. Plus how to trade without losing more than you can afford.
Glossary
The terms every odds, fee and legal page uses, each defined in a sentence or two.
| Event contract | A contract that pays $1 if a stated event happens and $0 if it does not. The whole category is built on this one instrument. |
| Implied probability | The chance a price assigns to an outcome. On a prediction market it is the price itself: a 62¢ contract implies 62%. Sportsbook odds have to be converted first. |
| Yes price / No price | The price of the contract that pays on the event happening, and of the one that pays on it not happening. The two sum to roughly $1; the Yes price reads as the probability. |
| Bid and ask | The best price a buyer is offering (bid) and the best price a seller will accept (ask). You buy at the ask and sell at the bid. |
| Spread | The gap between the best bid and best ask. You pay it on every round trip, on every venue, and no fee schedule lists it. |
| Consensus | On our cross-venue pages, the mean Yes price across every venue that quotes the question, reported with the venue count, because one venue is not a consensus. |
| Cross-venue spread | The gap between the highest and lowest Yes price for the same question on different venues, the difference a single venue will never show you. |
| Volume | The dollar value of contracts traded over a period, usually the last 24 hours. It measures activity, not how much is still at stake. |