Bid-Ask Spread Calculator

By Calxy · Calculation methodology

Enter a bid and an ask quote to get the spread, the midpoint, the spread as a percentage of the ask and of the midpoint, and what the spread costs on a trade.

Printed from Calxy · https://www.calxy.net/financial/bid-ask-spread-calculator

Bid-ask spread$0.50
currency units per share

0 – 1000000000000

currency units per share

1e-12 – 1000000000000

shares or units

Optional. Enter 0 to skip the trading-cost figures.

Bid-ask spread

$0.50

  • Spread as % of ask0.5000%
  • Spread as % of midpoint0.5013%
  • Midpoint price$99.75
  • Round-trip spread cost (buy at ask, sell at bid)$50.00
  • Cost vs midpoint on one side$25.00

Quotes change constantly; commissions, fees and price impact on larger orders are not included.

How this was calculated

Spread = ask − bid = 100 − 99.5 = 0.5.

Midpoint = (ask + bid) ÷ 2 = (100 + 99.5) ÷ 2 = 99.75.

Spread % of ask = 0.5 ÷ 100 × 100 = 0.5%; % of midpoint = 0.5 ÷ 99.75 × 100 = 0.5012531328%.

Round-trip cost = spread × quantity = 0.5 × 100 = 50.

Formulas

Spread = ask − bid. Midpoint = (ask + bid) ÷ 2. Spread % of ask = spread ÷ ask × 100, and spread % of midpoint = spread ÷ midpoint × 100. Quote sources differ on which base they use; the midpoint version is the more common measure of liquidity.

Buying at the ask and selling straight back at the bid loses the whole spread: round-trip cost = spread × quantity. Against the midpoint, each side of a trade costs half the spread.

Worked example

Bid 99.50, ask 100.00. Spread = 0.50; midpoint = 99.75; spread is 0.5% of the ask and 0.50125% of the midpoint. On 100 shares, a round trip costs 50.00 before commissions.

How to use the Bid-Ask Spread Calculator

Enter the two quotes and an optional quantity.

  1. Enter the bid

    The highest price buyers are paying.

  2. Enter the ask

    The lowest price sellers are accepting.

  3. Add a quantity

    Optional, to see the trading cost of the spread.

References

Frequently asked questions

What is the bid and what is the ask?

The bid is the highest price a buyer is offering right now; the ask is the lowest price a seller will accept. You buy at the ask and sell at the bid.

What is a good spread?

Heavily traded large stocks and ETFs often have spreads of a cent or a few hundredths of a percent. Thinly traded securities can have spreads of several percent.

Can the bid be above the ask?

Not on a normal quote. The calculator rejects that input.

Last updated . Results are estimates for informational purposes only.