Why Bid-Ask Spreads Exist and What They Represent
Every executed trade involves a buyer and a seller. Between the price a buyer is willing to pay and the price a seller is willing to accept, there is often a difference known as the bid-ask spread.
For traders operating in today’s electronic markets, bid-ask spreads provide a window into the interaction between buyers, sellers, liquidity, and current market conditions.
What Is a Bid-Ask Spread?
The bid-ask spread is the difference between the highest price a buyer is willing to pay for a security (the bid) and the lowest price a seller is willing to accept (the ask or offer). Collectively, bids and offers are referred to as quotes.
For example, if a stock has a highest displayed bid of $50.00 and a lowest displayed ask of $50.02, the bid-ask spread is $0.02.
The spread reflects the gap between the highest displayed price a buyer is currently willing to pay and the lowest displayed price a seller is currently willing to accept at a given point in time. In electronic markets, these displayed quotes generally change continuously as participants submit, modify, or cancel orders.
Why Do Bid-Ask Spreads Exist?
Bid-ask spreads exist because buyers and sellers may value a security differently at any given moment, resulting in buying and selling interest resting at different prices until orders interact.
A buyer placing a bid is indicating the maximum price they are currently willing to pay, while a seller placing an offer is indicating the minimum price they are currently willing to accept. The spread represents the difference between these two prices until an order interaction results in a trade.
Spreads are influenced by a range of factors, including liquidity, volatility, trading activity, news, and the characteristics of the security being traded.
Factors That Influence Bid-Ask Spreads
Several factors can influence the size of a bid-ask spread.
Liquidity
Liquidity refers to the availability of buyers’ and sellers’ quotes for a security. Securities with higher trading activity and greater participation may also have more displayed buying and selling interest available across multiple price levels. In some cases, this can contribute to narrower spreads.
Less actively traded securities commonly have fewer available quotes near the current market price, which can result in wider spreads. Liquidity is not determined by trading volume alone. Other factors, such as market depth and the availability of quotes at different price levels, also contribute to the overall trading environment.
Volatility
Market volatility can influence bid-ask spreads. During periods of increased price movement or uncertainty, market participants may adjust their displayed quotes more frequently. These changes can affect the prices at which buyers and sellers are willing to transact and may impact the spread.
Because market conditions can change quickly, spreads may expand or contract as participants respond to new information and changing levels of activity.
Market Conditions
Bid-ask spreads can vary depending on broader market conditions. Factors such as trading volume, economic events, company-specific news, economic news, and overall market activity can influence how participants provide and seek liquidity.
Spreads may also differ throughout the trading day and during extended trading hours, when participation and available liquidity may be lower. Market activity, available liquidity, and participation levels can change between the pre-market, market opening, regular trading hours, closing periods and post-market (after-hours) trading sessions. Liquidity is generally more limited in the pre- and post-market trading sessions.
Bid-Ask Spreads and Order Execution
The bid-ask spread is one factor to consider when evaluating the mechanics of an order execution.
A marketable order seeking immediate execution may interact with available displayed liquidity and, where applicable, other available liquidity (e.g. dark pools that do not display quotes) consistent with market structure and execution processes. A limit order specifies the price at which a participant is willing to transact.
The available liquidity at the time an order reaches the market can influence the price at which that order is executed. The spread is one component of the overall trading environment, alongside other factors such as order size, market conditions, market volatility, and execution venue.
For broker-dealers, order handling and routing processes are subject to regulatory requirements, including applicable best execution obligations. These processes consider factors relevant to the order and prevailing market conditions, including price, speed, and probability of execution.
Understanding Spreads in Modern Electronic Markets
Bid-ask spreads provide insight into the interaction between available buying and selling interest.
While the spread is often viewed as a simple difference between two prices, it reflects the interaction of buying and selling interest, available liquidity, and changing market conditions.
For traders, understanding bid-ask spreads provides additional context on how liquidity, orders, and execution interact across today’s electronic markets.
© 2026 Securities are offered by Lime Trading Corp., member FINRA, SIPC, NFA. Past performance is not necessarily indicative of future results. All investing incurs risk including, but not limited to, the loss of principal. Additional information may be found on our Disclosures Page. The material in this communication is not a solicitation to provide services to customers in any jurisdiction in which Lime Trading is not approved to conduct business. This communication has been prepared for informational purposes only and is based upon information obtained from sources believed to be reliable and accurate; however, Lime Trading Corp. does not warrant its accuracy and assumes no responsibility for any errors or omissions. The information provided is not an offer to sell or a solicitation of an offer to buy any security or a recommendation to follow a specific trading strategy. Lime Trading Corp. does not provide investment advice. This material does not and is not intended to consider the particular financial conditions, investment objectives, or requirements of individual customers. Before acting on this material, you should consider whether it is suitable for your particular circumstances and, as necessary, seek professional advice.