> ## Documentation Index > Fetch the complete documentation index at: https://docs.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. ## Initial Price * When a market is created, there are initially zero shares and no pre-defined prices or odds. * Market makers (a fancy term for traders placing limit orders) interested in buying YES or NO shares can place [Limit Orders](../trading/limit-orders) at the price they're willing to pay * When offers for the YES and NO side equal \$1.00, the order is "matched" and that \$1.00 is converted into 1 YES and 1 NO share, each going to their respective buyers. For example, if you place a limit order at \$0.60 for YES, that order is matched when someone places a NO order at \$0.40. *This becomes the initial market price.* Polymarket is not a "bookie" and does not set prices / odds. Prices are set by what Polymarket users are currently willling to buy/sell shares at. All trades are peer-to-peer. ## Future Price The prices displayed on Polymarket are the midpoint of the bid-ask spread in the orderbook — unless that spread is over \$0.10, in which case the last traded price is used. Like the stock market, prices on Polymarket are a function of realtime supply & demand. ### Prices = Probabilities In the market below, 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¢.