Polymarket Odds Explained

Converting a Polymarket price into probability

The basic conversion is direct:

This is a market-implied probability: the level at which participants are currently willing to trade. It is not an audited forecast or a promise that an event with a 95-cent price will occur.

How the displayed probability is calculated

Polymarket's current help guidance says the displayed probability is normally the midpoint between the best bid and best ask. If that spread is wider than $0.10, the interface uses the last traded price instead.

Example:

• Best bid: 0.44
• Best ask: 0.50
• Midpoint: 0.47

The page may therefore display roughly 47%, but an immediate buyer would need to accept the 50-cent ask. An immediate seller would receive the 44-cent bid.

If the last trade occurred at 0.60 and the current order book is 0.40 bid and 0.55 ask, a displayed last-trade value can be even less representative of the price available now. The order book is the source to use for execution.

Bid, ask, midpoint and last trade

Depth also matters. A 0.50 ask for ten shares does not mean 1,000 shares can be bought at 0.50. A larger order may fill at several higher prices.

How Polymarket payouts work

For a binary outcome held through resolution:

• a winning share redeems for $1;
• a losing share is worth $0; and
• profit before fees equals payout minus purchase cost.

Example: hold to resolution

You buy 200 YES shares at 0.35.

• Purchase cost: 200 × $0.35 = $70
• Gross payout if YES wins: 200 × $1 = $200
• Gain before fees: $200 − $70 = $130
• Loss if NO wins: $70

The attractive $130 potential gain exists because the market currently assigns YES a lower probability. The entire $70 purchase cost is at risk.

Example: sell before resolution

You buy 200 YES shares at 0.35 and later sell them at an average fill of 0.55.

• Sale value: 200 × $0.55 = $110
• Realized gain before fees: $110 − $70 = $40

This sale does not require the event to resolve. It does require sufficient buyers at the prices needed to fill the order.

Why YES and NO quotes can look confusing

Economically, the YES and NO outcomes form a $1 pair. If YES is 0.65, the complementary value is broadly 0.35.

The best displayed trading quotes may not add to exactly $1 because bids and asks are separate orders. A spread exists on both sides, and the front end may show a midpoint or last trade rather than a matched pair.

Focus on the side you intend to trade:

• for an immediate YES purchase, inspect the YES ask;
• for an immediate YES sale, inspect the YES bid;
• for a NO position, inspect the corresponding NO quotes; and
• for any large order, inspect quantities across several levels.

Are Polymarket odds accurate?

The price summarizes the views and incentives of active participants. That can make it informative, especially when new information is quickly reflected in orders.

It can still be wrong. Reasons include:

• traders have incomplete or incorrect information;
• the market has little liquidity;
• a large order temporarily moves the price;
• participants disagree about the resolution rules;
• the event has genuine uncertainty; or
• the displayed price is stale or sits inside a wide spread.

Accuracy should be evaluated over many resolved forecasts using a defined method, not by pointing to one dramatic success or failure.

A simple pre-trade odds check

1. Read the exact market rules.
2. Write down your own probability range.
3. Check the current bid, ask, and depth.
4. Use the actual intended entry price, not the midpoint.
5. Include the current fee and a realistic exit price.
6. Calculate the full loss if your outcome settles at zero.
7. Decide whether you would hold to resolution or try to sell.

If the idea only looks attractive at the displayed midpoint but not at the ask you must pay, it is not the same trade. Learn how to control the entry boundary in the limit-orders guide.

Limitations

Displayed-price logic, fee schedules, and the interface can change. Some markets have more than two named outcomes, but each individual outcome position still needs to be assessed using its own rules and order book. Examples on this page exclude fees and taxes so the mechanics remain visible; actual results can be lower.