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.

For example, in this market, the probability of 37% is the midpoint between the 34¢ bid and 40¢ ask. 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 shares would pay 40¢ for up to 4,200 shares, after which the price would rise to 43¢.