Bid-Ask Spread
The bid-ask spread is the difference between the best displayed buying price and the best displayed selling price.
How to calculate the spread
If a stock is quoted at $49.97 bid and $50.00 ask, the quoted spread is $0.03. Traders sometimes also consider spread as a percentage of price because a three-cent spread has a very different impact on a $5 stock than on a $500 stock.
Why spreads matter
Crossing the spread creates an immediate execution cost. If you buy at the ask and could immediately sell only at the bid, the position starts behind by roughly the spread before fees or price movement. For frequent traders, that friction can materially affect results.
What makes spreads wider
Spreads can widen when liquidity falls, uncertainty increases, volatility rises or market participants become less willing to quote aggressively. Thin securities, extended-hours sessions and fast-moving news events commonly exhibit less favorable spreads than calm, heavily traded markets.
Spread versus slippage
Spread and slippage are related but different. The spread is visible in the quote before the order. Slippage is the difference between the price a trader expected or intended and the actual execution price. A large order can experience both spread cost and additional slippage as it consumes liquidity at multiple price levels.
Practical questions before entering
- How wide is the spread relative to the expected target?
- Is the spread stable or jumping around?
- How much size is displayed near the inside market?
- Is the security unusually volatile right now?
- Would a limit order better match the execution objective?
Common questions
Is a one-cent spread always good?
It is generally favorable compared with a wider spread, but it does not guarantee deep liquidity or low volatility. Displayed size and how the quote behaves under pressure still matter.
Does the spread stay constant?
No. It can widen or narrow rapidly as orders enter or leave the market and as volatility changes.
Example: spread relative to target
Suppose a setup seeks a $0.15 move but the spread is already $0.08. A large portion of the expected move can be consumed by entry and exit friction. The same eight-cent spread may be much less significant for a trade targeting several dollars. Execution cost should be evaluated relative to the setup, not in isolation.
Source discipline
Market structure details can vary by security, venue, broker and order-routing arrangement. For formal rules and current exchange procedures, use primary sources such as the SEC, FINRA and the relevant listing/trading venue. See our Sources & Methodology.