Binary market

Also called YES/NO market · two-outcome market

A market with exactly two outcomes, quoted as a YES contract and a NO contract whose prices sum to $1 at fair value.

Exactly one of the two sides pays a dollar, so their fair prices add to a dollar. That identity is the single most useful fact in the whole venue, because it means buying NO at q is economically identical to selling YES at 1 − q. Every lock this site computes is built from it.

The two venues express it differently, and the difference matters when you go to execute. On Polymarket each side is its own token with its own order book, and the books mirror each other exactly — verified live against the CLOB, the NO side asking 0.997 for 9,694 shares is the same resting size as the YES side bidding 0.003 for 9,694. So each side's executable prices come straight from that side's own book. On Kalshi both sides of the book list resting bids, so buying YES crosses the NO bids: the executable YES ask is one minus the best NO bid, which the API also serves directly as a convenience field.

Multi-outcome events are assembled from binary legs. A five-candidate election is five YES/NO markets tied together by a flag that says how many of them can win, which is where negative risk and mutual exclusivity come in.

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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.