> ## Documentation Index
> Fetch the complete documentation index at: https://learn.polymarket.com/llms.txt
> Use this file to discover all available pages before exploring further.

# How are prices calculated?

> The prices probabilities displayed on Polymarket are the midpoint of the bid-ask spread in the orderbook.

Prices = probabilities.

The probabilities displayed on Polymarket are the midpoint of the bid-ask spread in the orderbook.

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For example, in this market, the probability of 76% is the midpoint between the 73¢ bid and 78¢ ask. The spread between them is 5¢. If the bid-ask spread is wider than 10¢, the probability is shown as the last traded price.

You may not be able to buy shares at the displayed probability / price because there is a bid-ask spread. In the above example, a trader wanting to buy Yes shares would pay 78¢ for up to 165 shares, after which the price would rise to 79¢.