Event contract

Also called binary option · outcome share

A contract that pays exactly $1 if a stated real-world outcome happens, and $0 if it does not.

Every instrument on Polymarket and Kalshi is one of these. The payout is fixed at one dollar, which bounds the price between zero and one and lets the price be read straight off as a probability — no odds conversion, no decimal-to-American translation. Prediction markets quote prices, not odds, and that is the practical reason why.

Kalshi lists them as regulated event contracts and calls one unit a contract. Polymarket issues them as on-chain outcome tokens and calls one unit a share. The instrument is the same: buy at 30¢ and you have risked 30¢ to make 70¢, with both the ceiling and the floor known before you enter.

That bounded payoff is what makes the arithmetic on this site possible. Position sizing runs on a known net payout multiple of (1 − cost) / cost rather than an estimate of downside, hedges collapse to a closed-form lock, and a full set of outcomes in a one-winner event has a computable total cost. It is also why the honest cost question is never the sticker price but the all-in cost — price plus fees — since a fee of a cent and a half on a 40¢ contract moves your breakeven by nearly four percent of the stake.

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Definitions describe how Polymarket and Kalshi behave and how WhaleTracks models them; venue rules and fee schedules can change, so confirm anything you size a position on with the venue itself. WhaleTracks is informational analytics, not financial advice. Past performance does not guarantee future results.