Lesson film
Watch this lesson as a short film
Bid, ask, mark and open interest: turn a wall of numbers into a clear menu.
What you'll learn
- Read the columns of a real options chain without getting lost
- Tell the difference between bid, ask, mark and last
- Identify which numbers matter most when you are selling
An options chain is just a menu. Pick a stock, pick an expiration date, and the chain lists every available strike with its current prices. Calls are usually on the left, puts on the right, strikes running down the middle. Once you know what each column means, a wall of numbers turns into a clear set of choices.
A worked chain
Here is a slice of a PFE (Pfizer) put chain with the stock trading around 28 dollars, expiration about 30 days out. We are shopping for a put to sell, so read down the put strikes.
| Strike | Bid | Ask | Mark | Volume | Open interest |
|---|---|---|---|---|---|
| 29 (put) | 1.55 | 1.65 | 1.60 | 210 | 1,940 |
| 28 (put) | 0.95 | 1.05 | 1.00 | 1,120 | 6,300 |
| 27 (put) | 0.55 | 0.65 | 0.60 | 880 | 5,150 |
| 26 (put) | 0.30 | 0.38 | 0.34 | 340 | 2,700 |
If you sold that 27-strike put, you would aim to collect around the mark of 0.60, which is 0.60 x 100 = 60 dollars for one contract. The bid of 0.55 is the worst-case fill; the ask of 0.65 is what a buyer pays. Placing a limit order near the mark usually gets you a fair fill.
Make a guess
Another put on the chain shows bid 1.10 and ask 1.30. Where is the mark, per share?
Volume and open interest: is anyone home?
Volume is how many contracts traded today; open interest is how many contracts are currently open in the market. Both tell you about liquidity — how easy it is to get in and out at a fair price. Notice the 28 strike has huge volume and open interest, while the 26 strike is thinner. Thin strikes have wider bid-ask spreads, which quietly costs you money on every trade.
What would you do?
Your call
Two strikes on the same stock have a mark near 0.60. Strike A: bid 0.58, ask 0.62, open interest 4,800. Strike B: bid 0.40, ask 0.80, open interest 35, and a 'last' of 0.75 from yesterday. How do you sell?
Fig. 1Interactive
Try it in YieldCove
When you log a sold put in YieldCove, the position page tracks your fill, premium and breakeven so you never have to redo this math by hand.
Key terms in this lesson
Each term has its own glossary page with a picture and related terms.
- BidGlossary entry
- The highest price a buyer is willing to pay right now. As a SELLER, this is roughly what you can collect if you sell immediately.
- AskGlossary entry
- The lowest price a seller is willing to accept right now. A buyer pays around this.
- Mark / MidGlossary entry
- The midpoint between bid and ask. A fair estimate of the option's real value, and a sensible price to aim your limit order at.
- LastGlossary entry
- The price of the most recent actual trade. Can be stale if the option has not traded in a while — trust bid/ask more.
Key takeaways
- An options chain is a menu of strikes and prices; calls left, puts right, strikes down the middle.
- Bid is what you collect as a seller, ask is what a buyer pays, mark is the fair midpoint, last can be stale.
- Liquidity matters: prefer tight bid-ask spreads and healthy open interest so spreads do not tax your returns.
Checkpoint
Knowledge check
Answer to lock in what you just learned.
As a SELLER getting filled quickly, which price are you most likely to receive?
You sell the PFE 27 put at the mark of 0.60. How much premium do you collect for one contract?
Why does a wide bid-ask spread hurt you?
Keep going
7 more chapters, from your first put to an expert playbook
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Educational content only — not financial advice. Options involve risk of loss and are not suitable for every investor.