Bid-Ask Spread Calculator
Calculate the bid-ask spread of a stock, ETF, option, bond or currency in price, percent of midpoint and basis points, plus the round-trip cost of trading a given quantity at market.
How it works
Spread = ask − bid · midpoint = (ask + bid) ÷ 2 · spread % = spread ÷ midpoint × 100 (some sources divide by the ask) · basis points = spread % × 100 · round-trip cost = spread × quantity
The bid is the highest price a buyer is offering and the ask the lowest price a seller will take; the gap between them is a hidden trading cost paid to market makers every time you use a market order. Quoting it as a percentage of the midpoint lets you compare liquidity across securities with different prices: large-cap stocks and major currency pairs often trade at a few basis points, while small caps, options and corporate bonds can cost 1% or more. Limit orders near the midpoint can reduce the cost.
Worked example
A stock quoted 99.95 bid and 100.05 ask has a spread of 0.10 around a midpoint of 100.00 — 0.100% of the midpoint, or 10.0 basis points. Buying 500 shares at the ask and selling them at the bid would cost 0.10 × 500 = 50.00, and a single market order costs 25.00 versus the midpoint.
Sources: Investor.gov (SEC) — Bid price and ask price · Investopedia — Bid-Ask Spread
Frequently asked questions
How do you calculate the bid-ask spread percentage?
Divide the spread (ask − bid) by the midpoint price and multiply by 100. Some brokers divide by the ask instead; for tight spreads the two are almost identical.
What is a good bid-ask spread?
For large, liquid stocks and ETFs a spread of a few basis points (a penny on a 100 share price) is normal. Spreads above about 0.5% suggest thin liquidity and are worth avoiding with market orders.
Why do spreads widen?
Low trading volume, high volatility, news events, market open and close, and small company size all make market makers demand a wider spread to compensate for risk.
How can I avoid paying the spread?
Use limit orders at or near the midpoint, trade liquid securities during regular hours and avoid trading right at the open or close.
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Educational estimate, not investment, trading or tax advice. Brokers, issuers and data providers use their own conventions, fees and figures — confirm with your broker, the issuer’s documents or a licensed adviser before acting.