Trading Volume

High trading volume on a Prediction Market contract generally means many participants are actively buying and selling, which creates competition among market makers and tightens the Bid-Ask Spread. On Kalshi and Polymarket, volume is typically displayed prominently on each contract page and used to rank market popularity. Contracts with millions of dollars in daily volume, such as major US political events, can support large position sizes with little Slippage. Conversely, contracts with only a few thousand dollars of daily volume may have wide spreads and shallow Depth of Market, making them expensive to trade even if the Implied Probability looks attractive. Volume is therefore one of the first filters a serious trader applies when evaluating a market.

Sudden spikes in volume without a corresponding price move can indicate informed traders absorbing supply or demand at current prices before a larger move occurs. Volume rising alongside a price move suggests strong conviction behind the trend, a useful signal for Momentum Trading strategies. When volume falls sharply while Open Interest stays high, it suggests existing holders are not trading, which can precede volatility when sentiment eventually shifts. On decentralized platforms, Automated Market Maker pools do not have discrete volume in the same sense as Order Book venues, but swap counts serve an analogous role. For any Expected Value calculation, knowing whether a market is actively traded protects against relying on a Last Price set by a single stale trade.