Select the contract before comparing prices
Confirm the underlying, expiration, call or put, strike and whether the contract is standard or adjusted. Two rows with the same strike but different expirations are not interchangeable. Check the quote timestamp and whether the data are delayed.
The bid is an indicated buying price; the ask is an indicated selling price. Size and available liquidity can change. Last trade may be stale and may have occurred at a different underlying price. A model “mark” or midpoint is a reference, not a promise that an order will fill.
Read a fictional row
| Strike | Bid | Ask | Volume today | Open interest |
|---|---|---|---|---|
| 95 | 7.20 | 7.60 | 150 | 800 |
| 100 | 4.80 | 5.20 | 320 | 1,450 |
| 105 | 2.70 | 3.10 | 90 | 600 |
For the $100 call, the spread is $0.40 per share, or $40 per contract. The midpoint is $5.00, but buying at $5.20 and immediately selling at an unchanged $4.80 would lose $40 before fees. This arithmetic shows why comparing only the last price can understate transaction costs.
Distinguish volume from open interest
Volume counts contracts traded during the stated session. Open interest counts outstanding contracts and is commonly updated after clearing. A trade can open, close or transfer exposure, so 320 contracts of volume does not necessarily add 320 to open interest.
High open interest does not certify a tight spread, available depth or a bullish forecast. Every contract has both a long and a short side. Price, liquidity and position structure require more information than an activity count.
Use a repeatable reading sequence
Read the row left to right, calculate the full contract amount, and compare nearby strikes and expirations without losing track of their different obligations. Then inspect implied volatility and Greeks using the platform’s units. Some interfaces show Greeks per share; others show position totals.
For a multi-leg spread, calculate the combined debit or credit and evaluate the net quoted market. Filling one leg alone changes exposure. An attractive screen midpoint across several legs may not be available as a package. The expiration and assignment lessons explain why execution is not the end of the analysis.
If open interest is 1,450 and today’s volume is 320, is tomorrow’s open interest necessarily 1,770?
Show the explanation
No. Trades can open or close positions or transfer them. Open interest is an outstanding-position count determined through clearing, not yesterday’s count plus all volume.
Sources and editorial notes
Original explanations and hypothetical examples prepared with AI assistance. Primary reference check dates are listed below. Numerical examples are hypothetical unless explicitly identified otherwise.
- FINRA: Reading Options and Their Terms
Strike, expiration, premium, exercise and options terminology. The chain, its bid/ask arithmetic and activity counts are original hypothetical teaching data. Checked October 17, 2026.
- OCC / OIC: Options Basics
Call/put rights and obligations, premium quotation and standard versus adjusted equity contract deliverables. Checked October 17, 2026.