📖 The Polymarket order book, explained simply

Every Polymarket price comes from an order book: two lists of real orders from real traders. One list is people offering to buy (bids), the other people offering to sell (asks) — each at a price and a quantity. There is no bookmaker setting a line; the "price" you see is simply where those two lists currently meet. Read the book once and market prices, spreads and slippage all stop being mysterious.

Bids, asks, and where "the price" comes from

Suppose a market's book looks like this:

• Asks (sellers): 500 shares at 47¢, 1,200 at 48¢, 3,000 at 50¢
• Bids (buyers): 800 shares at 45¢, 2,000 at 44¢, 5,000 at 42¢

Buy right now and you pay the best ask, 47¢. Sell right now and you receive the best bid, 45¢. The quoted "last price" is just wherever the most recent trade happened between those two. Nobody set 47¢ — a trader placed that order, and it stands until it fills or is cancelled. In Polyfox, any market screen shows this book, so you can look before you trade.

The spread: the cost of "right now"

The 2¢ gap between 45¢ and 47¢ is the spread. Buy at the ask and immediately sell at the bid, and the spread is what that round trip costs — before any fee. Busy markets have tight spreads (often 1¢); quiet ones can gap several cents. A wide spread isn't anyone charging you extra — it means few traders are competing to be on the other side of your trade, so the price of immediacy is high.

Depth and slippage: why size matters

The book above has only 500 shares at 47¢. Want 2,000 shares at market? You'd take all 500 at 47¢, then 1,200 at 48¢, then 300 at 50¢ — an average well above the quoted 47¢. That gap between quoted and average fill is slippage, and it grows with order size and shrinks with market depth.

This is why the same $500 order is a non-event in a busy election market and a price-moving splash in a market with $2,000 of total depth. Before sizing up, glance at the book: how much actually rests within a cent or two of the price?

How Polyfox market orders protect you

A Polyfox market order carries a slippage guard — by default it may fill up to 2% worse than quoted on buys and 10% on sells — and executes fill-or-kill: either the whole order fills within your limit, or nothing executes and nothing is spent. So a thin book gives you a failed order rather than a nasty average price. Copy trades have their own slippage settings.

When a limit order is the better tool

A market order pays the spread for immediacy. A limit order does the opposite: you name a price (0.001–0.999) and join the book yourself, filling only if the market comes to you — possibly partially, possibly never. It shines when the spread is wide (place your bid between the 45¢ bid and 47¢ ask), when you want a specific entry, or when you're in no hurry. Manual limit orders are good-till-cancelled; you can cancel any time and free the reserved funds.

This page is informational only and is not investment advice; positions can lose all of their value — see Legal notes.

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