Bid, Ask and the Spread - What Trading an Option Costs
Reviewed by Leon Moyer - Published October 9, 2026 - Last reviewed October 9, 2026
In this lesson
Read an option's bid, ask, last and mark, and calculate what the bid-ask spread costs on a trade.
The bid-ask spread is the gap between the highest price a buyer is offering for an option (the bid) and the lowest price a seller will accept (the ask). On an XYZ 50 call quoted at $2.15 bid and $2.25 ask, the spread is $0.10 per share, or $10 per contract.
That $10 is the loss on an immediate round trip if you buy at the ask and sell at the unchanged bid, and on some contracts it is many times larger. Reading the four prices on a quote, and understanding which prices are available, is one of the most practical skills on the chain.
What do bid and ask mean in options?
Every quote on the chain has two sides:
- The bid is the highest price anyone is currently willing to pay. If you sell with a market order, this is the quoted selling reference, not a guaranteed fill.
- The ask (also called the offer) is the lowest price anyone is currently willing to sell for. If you buy with a market order, this is the quoted buying reference, not a guaranteed fill.
A quote is often written as "bid x ask", so the XYZ 50 call from How to Read an Options Chain is "$2.15 x $2.25". In a normal two-sided quote, the ask is above the bid. Quotes can change before execution, and the displayed size may not cover your whole order. A fill can improve on the quote or be worse. The SEC explains why market orders do not guarantee a price.
Market makers and other participants post bids and offers; the best available prices across exchanges form the displayed quote. The Options Industry Council explains how option bids, offers and quoted size work.
Bid, mark and ask for the XYZ 50 call
Bid $2.15
Highest price buyers are offering
Mark $2.20
Midpoint of the bid and the ask
Ask $2.25
Lowest price sellers will accept
What is the mark price of an option?
The mark is the midpoint between the bid and the ask: mark = (bid + ask) / 2. For the 50 call, that is ($2.15 + $2.25) / 2 = $2.20.
The midpoint need not be a price anyone has traded at or will accept. Some brokers use it to value open positions; others use different marks, so check your platform's definition. Where the account values a position at the mark, it can show a small loss the instant you open it: you paid the ask, but the account values the contract at the midpoint.
What is the last price, and why can it mislead you?
The last price is the price of the most recent trade. On a busy contract it sits close to the mark: the 50 call might show a last of $2.22.
On a quiet contract, the last trade might be hours old. Suppose the XYZ 52 put last traded at $2.40 in the morning, and the stock has fallen since. The current quote is $2.55 x $2.75, so $2.75 is the current buying reference, not the earlier $2.40. The last price only tells you what someone paid then. The bid and ask show current quoted interest, subject to available size and price changes.
How much does the bid-ask spread cost you?
Imagine buying a contract and selling it straight back a moment later, with nothing else changing. You buy at the ask and sell at the bid, so you lose the spread. That is the cost of a round trip, and it is one plain formula: spread cost = (ask - bid) x 100 x the number of contracts.
The same idea is easier to compare across contracts as a share of the price. The 50 call's $0.10 spread is about 4.5% of its $2.20 mark. On the 63-day tab of the same chain, the 55 call is quoted at $0.85 x $1.25: a $0.40 spread on a $1.05 mark, or about 38%. That is a large execution hurdle; stock price, volatility, time remaining and the spread can all affect the price you can sell at.
Buy at the ask, sell straight back at the bid
Tight quote: 35-day 50 call ($2.15 x $2.25)
Wide quote: 63-day 55 call ($0.85 x $1.25)
Worked example
What the spread costs on five XYZ 50 calls
XYZ trades at $50.40. The 35-day 50 call is quoted at $2.15 x $2.25. Assume you buy 5 standard 100-share contracts at the ask, quotes stay unchanged, and fees are excluded.
- You pay the ask: $2.25 x 100 x 5 = $1,125.
- If your account values them at the midpoint: $2.20 x 100 x 5 = $1,100, so the position shows -$25 right away.
- If you sold immediately at the bid: $2.15 x 100 x 5 = $1,075, a round-trip loss of $50. That is the $0.10 spread x 100 x 5.
The spread also moves your break-even. Paying the ask, the break-even at expiration is $50 + $2.25 = $52.25. Had you been filled at the mark, it would have been $52.20.
On five contracts of a liquid option, the spread is a modest cost. On the wide 55 call, the same five-contract round trip would cost $0.40 x 100 x 5 = $200, on a position worth $525 at the mark.
Illustrative and hypothetical. The ticker and prices are invented for teaching, and the figures exclude commissions, fees, margin interest and taxes, which reduce real results. Past or hypothetical outcomes do not indicate future results.
How can you avoid overpaying the spread?
You cannot make the spread disappear, but you can avoid paying all of it every time:
- Use a limit order. A limit order names the most you will pay (or the least you will accept). Many traders start at or near the mark and adjust in small steps. A limit order is not guaranteed to fill, which is the trade-off. Limit Order vs Market Order for Options, later in this course, covers order types in detail.
- Check the spread against the price. Before you trade, divide the spread by the mark and compare it with nearby strikes and expirations. The wider it is relative to the mark, the more an immediate round trip at the quoted ask and unchanged bid would cost. Also check quoted size.
- Prefer liquid contracts. Spreads are usually tightest at the expirations and strikes where the most trading happens. Volume and Open Interest shows how to find them.
Check your understanding
An option is quoted at $1.10 x $1.20. What is the mark, and what is the spread per contract?
Show answer
The mark is $1.15, the midpoint of $1.10 and $1.20. The spread is $0.10 per share, or $10 per contract.
You buy 3 contracts at a $1.20 ask and sell them right back at the $1.10 bid. What did the round trip cost, before fees?
Show answer
$30. The spread is $0.10 per share, times 100 shares, times 3 contracts.
A contract's last price is $2.40, but its quote is $2.55 x $2.75. What is the quoted buying reference, and is it guaranteed?
Show answer
$2.75, the ask. The last is an earlier trade. A market order may fill at a different price as quotes and available size change.
Key takeaways
- The bid is what buyers will pay and the ask is what sellers want. The displayed quote does not guarantee a market-order fill.
- Here the mark is the midpoint; broker valuation methods vary and a midpoint fill is not assured.
- The last price is only the most recent trade and can be stale; trade off the current bid and ask.
- An immediate round trip at an unchanged ask and bid costs the spread x 100 x the number of standard contracts, before fees. Compare the spread to the mark to see how expensive a contract is to trade.
Common questions
Do you buy options at the bid or the ask?
The ask is a reference for buying and the bid for selling. Market orders seek the best available price, but the displayed quote is not a guaranteed fill. A limit order lets you name a price in between, but it only fills if someone takes the other side at that price.
What is a good bid-ask spread for options?
There is no fixed number. Compare the spread with the option's midpoint and with nearby strikes and expirations, then check quoted size. A wider spread relative to the option's price raises the cost of an immediate round trip if you buy at the ask and sell at the unchanged bid.
What is the mark price of an option?
Here, mark means the midpoint between the bid and the ask. Broker valuation methods differ, which is why a position can show a small loss the moment you buy at the ask.
Why is the last price outside the bid and ask?
The last price is the most recent trade, which may have happened minutes or hours ago. If the stock has moved since then, the current bid and ask can be far from it, so use the bid and ask, not the last price, to judge what a contract is worth now.