Bid-Ask Spread

The bid-ask spread is the difference between the highest displayed buying price and the lowest displayed selling price for an instrument.

The spread is an implicit trading cost because an immediate buyer typically pays near the ask while an immediate seller receives near the bid. It often narrows when many participants compete and quoted size is abundant, then widens during volatility, thin trading, or market stress. The displayed spread does not include every cost and can change before execution, especially for large orders.