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Prices are probabilities

Every contract on Polymarket US is priced between $0 and $1. The price represents the market’s collective belief about how likely an outcome is. If you buy a YES contract at $0.55 and the outcome happens, the contract settles at $1.00 — you profit $0.45 per contract. If it doesn’t happen, it settles at $0.00 and you lose your $0.55.

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The order book

Polymarket US runs a central limit order book. Prices aren’t set by Polymarket — they come from traders placing buy and sell orders against each other. The order book has two sides: The spread is the gap between the best bid and the best ask. A tight spread means the market is liquid. A wide spread means fewer people are trading. The BBO (best bid and offer) is the tightest price on each side — the highest bid and the lowest ask. This is the price you’d trade at if you placed a market order right now.

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How trades happen

When you place a market order, it fills immediately at the best available price on the other side of the book. You’re a taker — you’re taking liquidity. When you place a limit order at a specific price and it doesn’t fill immediately, it sits on the book waiting. You’re a maker — you’re providing liquidity for others to trade against. If your limit order’s price crosses the best available price on the other side, it fills immediately (like a market order). Otherwise, it rests on the book.

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Settlement

When a market resolves, every contract settles at either $1.00 (YES won) or $0.00 (NO won). The exchange handles this automatically — winning contracts are credited to your balance, losing contracts go to zero.

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Market states

A market goes through different states during its lifecycle: