How to Read an Options Chain: Bid, Ask, Volume, Open Interest, and IV

An options chain is the table a broker or exchange shows of every listed option on one underlying for one expiration date, with calls on one side, puts on the other, and the strike prices running down the middle. Each row tells you what buyers are bidding, what sellers are asking, how much traded today, how many contracts are open, and usually the implied volatility and delta for that strike.

In short: read a chain by first choosing the expiration, then finding the strike, then looking at the bid (the price you can sell at now) and the ask (the price you can buy at now). The gap between them is a real cost. Volume is contracts traded today; open interest is contracts still open, typically as of the previous day’s close. Implied volatility (IV) is the volatility the price implies, and delta estimates how much the option moves per $1 in the stock. All prices are per share; multiply by 100 for the cost of one standard contract.

The misconception: “the last price is the price”

Many people look at the Last column and assume that’s what an option costs. The last price is simply the most recent trade, which might have happened hours ago when the stock was somewhere else. What you can actually trade at right now is the bid and the ask. In a thinly traded option, the last price can be meaningless.

The layout

Most chains use a “straddle” layout:

Calls on the left, puts on the right, sharing a strike column in the middle.
Strikes run from low at the top to high at the bottom.
In-the-money options are often shaded. For calls, that’s strikes below the stock price; for puts, strikes above it. (See in the money vs out of the money.)
An expiration selector at the top switches between dates (weeklys, monthlies, LEAPS), often showing the days remaining. How those dates are set is in strike prices and expiration dates.

A worked chain

Hypothetical Maple Widgets Inc. trades at $50.00. Here is a hypothetical chain for options expiring in 30 days. The prices are built from a Black-Scholes model with volatility around 30%; volume and open interest are invented for illustration.

Calls

Strike	Bid	Ask	Last	Volume	Open int.	IV	Delta
$45	5.25	5.50	5.30	12	840	30.8%	0.90
$47.50	3.25	3.45	3.40	85	1,920	30.4%	0.75
$50	1.75	1.85	1.80	1,240	5,310	30.0%	0.53
$52.50	0.82	0.88	0.85	960	4,100	30.4%	0.32
$55	0.33	0.38	0.35	610	6,250	30.8%	0.16

Puts

Strike	Bid	Ask	Last	Volume	Open int.	IV	Delta
$45	0.20	0.24	0.22	430	3,880	30.8%	-0.10
$47.50	0.65	0.71	0.68	520	2,640	30.4%	-0.25
$50	1.58	1.68	1.62	890	4,470	30.0%	-0.47
$52.50	3.10	3.30	3.20	75	1,150	30.4%	-0.68
$55	5.05	5.30	5.15	9	380	30.8%	-0.84

Column by column

Bid and ask

Bid: the highest price someone is currently willing to pay. If you sell at market, you get roughly the bid.
Ask (or offer): the lowest price someone is willing to sell at. If you buy at market, you pay roughly the ask.
Mid (midpoint): halfway between. Some brokers show it as “Mark.” It’s a reference, not a guaranteed fill.

Worked example. Buying one $50 call at the ask costs $1.85 x 100 = $185. If you immediately sold it at the bid, you’d get $1.75 x 100 = $175. That $10 round-trip cost is about 5% of what you paid, before commissions and fees, and the stock hasn’t moved at all.

The spread matters more on cheap options. The $55 call’s spread is only $0.05, but the midpoint is about $0.355, so the spread is about 14% of the option’s value. The $45 put’s spread of $0.04 on a midpoint of $0.22 is about 18%. Low premiums with wide spreads are one reason short-term, far out-of-the-money options are so costly to trade.

Bid and ask are set mainly by market makers, firms that continuously quote both sides. Their role is covered in how options markets work.

Last and change

Last is the price of the most recent trade; Change (often shown) compares it with the previous day’s closing value. Both can be stale. The $55 put above traded only nine contracts today, so its last price may not reflect where it would trade now.

Volume

Volume is the number of contracts that have traded today. It resets every day. High volume generally means a more active market and often tighter spreads. In the chain above, the at-the-money $50 strike has the most activity, which is typical.

Volume doesn’t tell you whether trades were buys or sells; every trade has both.

Open interest

Open interest is the number of contracts that are open (not yet closed, exercised, or expired) at a strike. OCC tracks open positions, and chains usually show open interest as of the end of the previous trading day, so it doesn’t change during the session.

If a buyer and a seller both open new positions, open interest rises by the number of contracts.
If both close existing positions, it falls.
If one opens and one closes, it stays the same.

Open interest helps you judge liquidity: a strike with thousands of open contracts is usually easier to trade than one with a few dozen. But like volume, it doesn’t reveal who is long and who is short.

Implied volatility (IV)

Implied volatility is the volatility figure that, put into a pricing model, reproduces the option’s market price. It’s expressed as an annualized percentage. In the chain, IV is lowest at the money and rises at strikes farther away; this pattern, called a smile or skew, is common in real markets. Comparing IV across strikes and dates is more meaningful than comparing raw prices. See implied volatility explained.

Delta and other Greeks

Many chains show delta, and some add gamma, theta, and vega. Delta estimates how much the option price changes for a $1 move in the stock: the $50 call’s delta of 0.53 means roughly $0.53 per share, or $53 per contract, for a $1 rise in Maple. Puts have negative deltas because they lose value as the stock rises. All of the Greeks are introduced in option Greeks explained.

Putting it together: reading one row

Take the $52.50 call:

Cost to buy now: about $0.88 x 100 = $88.
Breakeven at expiration: $52.50 + $0.88 = $53.38, about 6.8% above the current price, within 30 days.
Spread: $0.06, roughly 7% of the midpoint.
Activity: 960 contracts today and 4,100 open, so reasonably liquid in this example.
Delta 0.32: gains about $32 per contract for the first $1 the stock rises.
If Maple is at $52.50 or below at expiration: the call expires worthless, and the $88 is gone.

Nothing in the chain tells you whether this or any other contract is a good idea. It tells you the price of a bet and how easy it is to get in and out.

Practical points

Check the expiration first. Similar-looking chains for different dates can have very different prices.
Check the underlying price shown at the top, and whether it’s real-time or delayed.
Use limit orders. A market order on a wide-spread option can fill at a poor price. A limit order sets the most you’ll pay or least you’ll accept.
Watch for non-standard contracts. After corporate actions, adjusted options can appear with odd deliverables and different symbols. Their prices won’t line up with the regular chain.
Canadian chains on the Montréal Exchange quote in Canadian dollars, with the same 100-share contract size for equity options.

What can go wrong

Trading off the last price instead of the current bid and ask.
Ignoring the spread. A round trip at the bid and ask can cost a significant share of a small premium.
Reading volume as direction. Heavy call volume doesn’t mean people are “betting on a rise”; many of those trades may be sales.
Mistaking open interest for an endorsement. Large open interest at a strike says many contracts exist there, nothing about where the stock will go.
Delayed data. Free chains are sometimes 15 minutes delayed, which is an eternity in a fast market.

Common questions

Why do some strikes show a bid of zero?

A zero bid means no one is currently willing to pay anything for that option, usually because it is far out of the money and close to expiration. You may be able to buy it at the ask, but you may not be able to sell it at all before it expires.

Why does the chain change when I switch expirations?

Each expiration is a separate set of contracts. Longer-dated options carry more time value, may have different implied volatilities, and often have different strikes listed, so the same strike can look very different from one date to the next.

What is the “Mark” or “Mid” column?

It’s the midpoint between the bid and the ask, used by many brokers to value positions in your account. It is a reasonable estimate of fair value in liquid options, but you can’t count on trading there.

The takeaway

An options chain lists every strike for one expiration, calls on one side and puts on the other. The bid and ask are the prices that matter; the spread between them is a cost you pay. Volume shows today’s activity, open interest shows contracts outstanding, and IV and delta summarize how the market is pricing each strike. Reading a chain well is about understanding costs and liquidity, not finding a signal.