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How to Read a Polymarket Order Book

Guide with a live order book · updated September 23, 2026

An order book lists every resting order to buy (bids) and sell (asks) an outcome. On September 23, 2026 the book for 25 bps increase in “Fed Decision in October?” showed a best bid of 67.0¢ (58,487 shares) and a best ask of 68.0¢ (25,482 shares): a 1.0¢ spread around a 67.5¢ midpoint — the number Polymarket shows as the probability.

Live example: Fed Decision in October? — 25 bps increase

Bids (buyers)

Price	Shares	Cumulative $
67.0¢	58,487	$39,186
66.0¢	60,111	$78,860
65.0¢	2,668	$80,594
64.0¢	2,536	$82,217
63.0¢	6,150	$86,092
62.0¢	5,000	$89,192
61.0¢	3,784	$91,500
60.0¢	4,528	$94,217

Asks (sellers)

Price	Shares	Cumulative $
68.0¢	25,482	$17,328
69.0¢	104,920	$89,723
70.0¢	35,914	$114,862
71.0¢	28,964	$135,427
72.0¢	6,205	$139,895
73.0¢	562	$140,305
74.0¢	10,392	$147,995
75.0¢	12,010	$157,003

Tick size 0.01 · minimum order 5 shares · last trade 32.0¢ · snapshot September 23, 2026, refreshed twice a day.

What a market buy would cost right now

Spend	Shares	Average price	vs best ask
$100	147	68.00¢	+0.00¢
$1,000	1,471	68.00¢	+0.00¢
$10,000	14,706	68.00¢	+0.00¢
$50,000	72,833	68.65¢	+0.65¢

Walks the asks from the cheapest up; fees not included (see Polymarket fees).

How to read it

📗 Bids are buy orders: the highest bid is what you get if you sell right now.
📕 Asks are sell orders: the lowest ask is what you pay if you buy right now.
↔️ Spread = best ask − best bid. A 1¢ spread is tight; wide spreads mean you give up more to trade instantly.
🎯 Midpoint = halfway between best bid and best ask — the probability shown on Polymarket. If the spread is wider than 10¢, Polymarket shows the last trade instead (Polymarket Help Center).
📚 Depth = how many shares sit at each price. Thin depth means a large order moves the price (slippage).
🧾 Maker vs taker. A limit order that rests on the book is a maker order (no fee); an order that fills against the book pays the taker fee.

Why a YES bid is also a NO ask

Every market has two outcome shares that together pay $1. Buying YES at 68¢ is economically the same as selling NO at 32¢, so the YES and NO books mirror each other: a bid for YES at p appears as an ask for NO at 1 − p.

Frequently asked questions

What is the spread on Polymarket?

The gap between the best ask (lowest sell price) and the best bid (highest buy price). Liquid markets often trade with a 1¢ spread; thin markets can be several cents wide.

Why does the Polymarket price differ from what I pay?

The displayed probability is the midpoint of the spread (or the last trade when the spread is wide). A market buy pays the ask — and more if your order is larger than the shares offered at the best price — plus any taker fee.

How do I avoid slippage on Polymarket?

Use limit orders at the price you want, split large orders, and check the depth first: the table above shows what spending $100 to $50,000 would cost right now.

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