On 10 Jun 2026 the 23,500 Nifty call in the June chain carried 44,81,555 units of open interest. Divide by the lot size, 65, and the same count reads 68,947 contracts. Same cell, two numbers, 65 times apart. Put one beside the other and you can "prove" almost anything. That is how most chain mistakes start: a column counts one thing and the reader assumes another. I check the unit before I read anything else on a chain. This lesson reads one chain from the strike column outwards, one column at a time. Every figure comes from the end of day files of 10 Jun 2026, so nothing here is live and nothing is a view on where the index goes next.
3By the end you can
- Say what every column of an option chain counts, and in which unit.
- Find the at the money row from the future, not from the spot.
- Explain why the largest open interest is not a floor or a ceiling.
The idea, plainly
Think of a chain as a ladder. Each rung is a strike, a level of the index. Calls hang on the left of the rung, puts on the right, and the same columns repeat on both sides. Read across one rung before you read down a column. A call and a put at one strike tell you more about each other than two calls tell you about the market.
A chain is two mirrored tables around one strike column
| Calls | Strike | Puts | ||
|---|---|---|---|---|
| OI | Settle | Settle | OI | |
| 16.6L | 467.85 | 23,000 | 221.05 | 52.2L |
| 21,255 | 437.55 | 23,050 | 239.25 | 1.1L |
| 2L | 405.90 | 23,100 | 258.10 | 5.2L |
| 35,100 | 374.55 | 23,150 | 278.95 | 1.3L |
| 8.2L | 347.70 | 23,200 | 300.60 | 17.7L |
| Spot 23,214.95 | ||||
| 2.9L | 321.65 | 23,250ATM | 322.05 | 3L |
| 11.2L | 294.60 | 23,300 | 347.65 | 14.7L |
| 2.7L | 272.55 | 23,350 | 371.80 | 2.7L |
| 10.6L | 248.10 | 23,400 | 398.75 | 11.3L |
| 1.4L | 226.65 | 23,450 | 426.80 | 1L |
| 44.8L | 206.25 | 23,500 | 456.80 | 38.8L |
Shaded cells are in the money. Outlined cells hold the most open interest among the strikes shown. OI is in units and volume is in contracts; L is lakh and Cr is crore.
The term this section turns on: Open interest
- Strike. The index level the contract is written on. A row label, not a forecast.
- LTP. The price of the last trade, in rupees per unit. On a quiet strike it can be hours old.
- Settle. The exchange's end of day price, used to mark open positions. It is not always a trade.
- Volume. Contracts traded today. It is not open interest.
- OI. Contracts still open, one count for each buyer and seller pair. It is not the size of one side.
- Change in OI. OI today minus OI yesterday. Contracts added or closed, not buying or selling pressure.
- IV. The yearly volatility that makes an option model return this price. A price in volatility terms, not a forecast.
Forward ≈ strike + call − put
Read 5 more paragraphs, 230 words
Three things to see in the table. The spot line sits between 23,200 and 23,250, but the ATM tag sits on 23,250. Call and put prices swap places at that row: calls cost more below it, puts cost more above it. And open interest is lumpy, with the hundreds far fatter than the fifties between them.
Seven things sit on a full chain. Each counts something different.
Mind the unit in the OI column. NSE's end of day file counts open interest in units, so one contract adds 65. A chain screen may count contracts instead. Divide units by 65 to get contracts. On a few strikes the division is not clean, because part of the count was opened under the older lot size. Compare volume with open interest only after both are in contracts.
Now the at the money row. It is the strike nearest the forward, the level at which the index is priced for that expiry. For a monthly expiry the forward is the future of the same month. A weekly expiry has no future, so the forward is read off a call and a put at one strike.
Call and put here are the prices at that one strike. The spot is the wrong yardstick. It leaves out the net carry between today and expiry, which is why the future sits above it here.
Worked example: the 10 Jun 2026 June chain
The index closed at 23,214.95 and the June future settled at 23,240.10. The strike nearest the spot was 23,200. The strike nearest the future was 23,250. Which one is at the money? Check the prices. At 23,250 the call settled at 321.65 and the put at 322.05, almost equal. At 23,200 the call cost 347.70 and the put 300.60, a gap of 47.10. Equal call and put prices mark the forward, and here the forward is the future's level, not the spot's.
| The 23,250 row | Call | Put |
|---|---|---|
| Settle, rupees per unit | 321.65 | 322.05 |
| One lot of 65 units, rupees | 20,907.25 | 20,933.25 |
| Open interest, units | 2,92,110 | 2,98,285 |
| Open interest, contracts | 4,494 | 4,589 |
| Change in OI, units | −1,47,160 | −1,03,285 |
| Volume, contracts | 10,854 | 9,004 |
| IV | 15.1% | 14.6% |
Open interest piles up on round strikes, on both sides
Trading is thick at the hundreds and thin at the strikes between them
IV is not one number: it changes with the strike
Read 5 more paragraphs, 257 words
Run the formula on the 23,200 row: strike plus 47.10 gives 23,247.10. The future settled at 23,240.10, so the two forwards sit 7.00 apart. On an index this size that is close. The four prices were not struck at one instant.
Now the change column. At 23,200 the call lost 2,741 contracts of OI, so positions were closed there. At 23,400 the call gained 2,953 contracts, so new positions were opened. In both cases the number says that contracts moved. It does not say whether buyers or sellers did it.
Volume and OI answer different questions. Volume is the day's traffic, OI is what stays parked. The 23,500 call traded 94,808 contracts against 68,947 open at the close, 138% of the open count in one session. In units, that same pair would look like a trickle.
Not every row is a market. NSE lists strikes far from the future, and many of them sit idle. The 22,250 call had 0 contracts traded and 13 open. The sheet still prints 1,097.10. No trade stands behind that price. Check volume before you trust a number on a far row.
Last, the IV column. It is not flat. At about the same distance either side of the future, the 22,500 put showed 16.2% and the 24,000 call 14.4%. The usual single reference is the at the money IV, read at the future between the two nearest strikes: 15.0% on this chain. The shape across strikes is called the smile, and a later lesson takes it apart.
The common mistake
The claim goes: The strike with the highest open interest is the support or resistance for the index.
A big number looks like a big commitment, so it sounds like logic. Test it on this chain. The 23,500 strike holds 44,81,555 units on the call side and 38,83,945 on the put side. If a big count made a wall, that one strike would be a ceiling and a floor at once. Widen the view from the table to the chart and the biggest call count moves to 24,000, with 80,36,850 units. Every open contract has a buyer and a seller. The count shows where positions sit. It does not show who is right, who is hedging a share portfolio, or who closes the position by lunch.
Key takeaways
- Calls sit on the left, puts on the right, the strike in the middle.
- Open interest is what stays open. Volume is what traded today.
- Check the unit: the day file counts units, a screen may count contracts.
- At the money means nearest the future, not nearest the spot.
- A far strike can print a price with no trade behind it. Check volume.
- The biggest open interest shows where positions sit, not where the index turns.
Before you trade. Derivatives trading carries a high risk of loss. SEBI's study "Profitability of Individual Traders in the Equity Derivatives Segment (FY25 to FY26)" (August 2026) found that 87.7% of individual traders in equity F&O made net losses in FY26, with aggregate net losses of Rs 91,685 crore. Read the SEBI study