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Key Takeaways
- The bid is the highest displayed buy price; the ask is the lowest displayed sell price.
- The midpoint equals the average of bid and ask. Spread width equals ask minus bid.
- Compare spread percentage and displayed size to evaluate execution cost across contracts.
- Read the execution against the quote, then connect the trade side, contract, and related legs.
- A platform’s mark is its own valuation price, set at the midpoint on some platforms and by a model on others, so check which one the P&L uses.
What are bid, ask, and midpoint?
The bid is the highest displayed price buyers will pay. The ask, also called the offer, is the lowest displayed price sellers will accept. The midpoint is the average of the two, and the bid-ask spread is ask minus bid. Together they describe the market available for a stock or option at that moment.
For an option quoted $2.00 bid and $2.20 ask, the midpoint is $2.10 and the spread is $0.20. Displayed size states how many contracts are quoted at each price. Read price and size together to compare the available market with your order.
US listed options trade across multiple exchanges. The national best bid and offer, or NBBO, combines the best displayed prices across those venues.
How do you calculate the spread cost?
Use three calculations:
- Midpoint: ($2.00 + $2.20) ÷ 2 = $2.10.
- Spread: $2.20 − $2.00 = $0.20.
- Spread percentage: $0.20 ÷ $2.10 × 100 = 9.5%.
With a 100 premium multiplier, ten contracts bought at $2.20 cost $2,200. The same quantity filled at $2.10 costs $2,100, a $100 improvement.
With the quote unchanged, buying at $2.20 and selling at $2.00 produces a $200 round-trip cost across ten contracts. Each side is $0.10 from the midpoint, so the two sides total one full $0.20 spread per quoted unit.
Formula
Midpoint = (bid + ask) / 2; Spread = ask − bid; Spread percentage = 100 × (ask − bid) / midpoint- Multiply quoted option premium by contracts and the premium multiplier to calculate cash value.
- Compare executions with the national best bid and offer recorded for the execution time.
- Use spread percentage to compare execution cost across contracts with different premium levels.
Worked Example
An XYZ call is quoted $2.00 bid by $2.20 ask, with 45 contracts bid and 38 contracts offered. A trader wants to buy 10 contracts and compares paying the offer with working a midpoint order.
- Midpoint: ($2.00 + $2.20) / 2 = $2.10
- Spread: $2.20 − $2.00 = $0.20, or $0.20 / $2.10 = 9.5 percent of the midpoint
- Cost at the offer: $2.20 × 10 × 100 = $2,200
- Cost at the midpoint: $2.10 × 10 × 100 = $2,100, a $100 difference
Ten contracts filled at $2.10 cost $100 less than ten filled at $2.20, using a 100 premium multiplier. With the quote unchanged, buying at $2.20 and selling at $2.00 costs $200 across ten contracts. That is one full quoted spread for the round trip.
How do traders use the midpoint?
A buy limit sets the maximum acceptable purchase price. A sell limit sets the minimum acceptable sale price. A midpoint order requests a price inside the displayed spread; a marketable limit reaches the opposing quote while retaining its stated price boundary. Confirm filled quantity and execution price in the order report.
Exchange auctions and competing liquidity providers also produce fills inside the spread. Compare the execution with the quote at that moment to measure price improvement.
A platform’s mark is its selected valuation price. Some marks use the midpoint; others use a theoretical model or another convention. Read the platform’s mark definition before trusting an open P&L, because a model mark can sit away from the $2.10 midpoint.
How do you compare liquidity across options?
Compare nearby strikes and expirations using spread percentage, displayed size, volume, and open interest. A narrow dollar spread can still represent a large part of a low-priced option’s premium. Translate that spread into the cash cost of your intended quantity.
Read depth and auction activity together. Displayed quotes describe visible resting size; reserve liquidity and auction responses add other execution opportunities. Match the order size to the available market and the price you intend to pay.
How do bid and ask help read options flow?
Start with the print’s price relative to the bid, ask, and midpoint. Then read call or put, strike, expiration, premium, size, and related executions. Ask-side call buying adds positive call delta; ask-side put buying adds negative put delta. Combine the legs to identify the package’s exposure.
Options flow shows each print with its quote context beside nearby contracts, and the options profit calculator connects the selected strike and premium with the planned payoff.
Limitations of bid, ask, and midpoint quotes
- Size the order to the displayed quote. It shows visible resting size only; reserve liquidity and auction responses can add to it, and an order larger than the displayed size can fill at more than one price.
- Use the midpoint as the benchmark for a fair fill, and confirm the fill in the execution report. A midpoint order fills only when matching liquidity arrives at that price or better.
- Judge every fill against the quote at its execution time, since a quote from another moment misstates both the cost and any price improvement.
- A dollar spread hides relative cost. A $0.10 spread is 33.3% of a $0.30 premium and 1.7% of a $6 premium, so compare spread percentage.
- Read the whole package before calling a print bullish. An ask-side call can be one leg of a spread, so related legs and the contract type complete the read.
Bottom line
The bid, ask and midpoint describe the market available at a moment: what buyers will pay, what sellers will accept, and the price halfway between. Use the midpoint to set limit prices, spread percentage and displayed size to compare liquidity, and the quote at execution time to judge every fill.
Clear answers
Frequently Asked Questions
Sources and Further Reading
- Options Industry Council: Understanding the Bid and Ask Prices for Options
- Options Industry Council: Mark to Market, Where Every Option Finds Its True Value
- Cboe: U.S. Options Exchange Crossing Orders and AIM Price Improvement
- Cboe Options Lite: NBBO, trade, and quote data
How entries are sourced, calculated and updated: editorial methodology.