An option chain is a table of every strike price of one expiry. The call figures sit on one side and the put figures on the other. Each row holds open interest, traded volume and the last traded price for that strike, on both sides.
Definition and Formula
The chain is organised around the strike price, which runs down the middle. Everything to one side of it belongs to the calls (CE) at that strike. Everything to the other side belongs to the puts (PE).
Open interest is a count of contracts still open at that strike. It is not the number of contracts traded during the day — that is volume, a separate column. A strike can carry very large open interest and see almost no trading, and the reverse can also happen.
The strike closest to the current price of the underlying is called the ATM strike. Strikes are usually shown a few steps on either side of it. Those rows carry most of the activity, and a full chain runs to dozens of rows.
The last traded price column records the price at which that contract last changed hands. On a strike far from the current price, that trade may have happened some time ago. So the figure can be older than the ones next to it. The chain does not stamp each price with its own time.
Strikes are listed at fixed intervals set by the exchange, and the interval differs between instruments. Nifty strikes are listed 50 points apart, while Bank Nifty strikes are listed 100 points apart. So a window of the same number of strikes covers a different span of price on each instrument.
Formula: ATM strike = the listed strike nearest the underlying price · Change in OI = current OI − OI at the last close
A Worked Example
| Underlying | 24,280.00 |
|---|---|
| Strikes in the chain | 24,200 · 24,300 · 24,400 |
| Call OI at those strikes | 12.5 L · 21.0 L · 16.8 L |
| Put OI at those strikes | 24.5 L · 17.2 L · 9.4 L |
| ATM strike | 24,300.00 |
|---|---|
| Strike with the highest Call OI | 24,300.00 |
| Strike with the highest Put OI | 24,200.00 |
| Total Call OI | 50,30,000.00 |
| Total Put OI | 51,10,000.00 |
Each result is computed by the same code that builds the option chain pages on this site, from the chain above.
What This Number Tells You
The chain states, strike by strike, how many contracts are open and how many changed hands. Those are counts of what has already happened.
The ATM strike states which listed strike currently sits closest to the price of the underlying. It moves as the underlying moves.
And What It Does Not Tell You
Open interest does not state who is on which side. Every open contract has a buyer and a writer, and the chain shows only that the contract exists.
A large figure at one strike is not a statement about where the price will go. It is a count of contracts, and contracts are opened and closed for reasons the chain does not record.
The chain describes the present moment only. Open interest changes through the session and again on the next one.
Frequently Asked Questions
What is the difference between open interest and volume?
Open interest counts contracts still open at that strike. Volume counts contracts that changed hands during the session. A contract that was opened and closed the same day adds to volume and leaves open interest unchanged.
Why does the chain show only a few strikes?
A full chain runs to dozens of strikes, most of them far from the current price. This site shows a window around the ATM strike, and states how many strikes that window covers.
What does CE and PE mean?
CE is a call option and PE is a put option. On this site both appear at every strike, so each row lets the two sides of the same strike be read together.
Does an option chain apply to one expiry or all of them?
One. Each expiry has its own chain, and the same strike carries different figures in other expiry dates.
Why is the last traded price sometimes stale?
Because it records the last trade in that contract, whenever it happened. On a strike far from the current price, that may have been some time earlier in the session.