Open interest (OI) is the number of option contracts at a strike that are still open: bought and sold, and not yet closed, exercised or expired. In the option chain it is the outermost column on each side, call OI on the far left and put OI on the far right.
How a trade changes open interest
Every option contract has two sides: a buyer, who pays the premium, and a writer, who receives it. OI counts contracts, not people, and it moves only when a trade opens or closes a position:
- A new buyer trades with a new writer: OI goes up by one.
- Someone closing a position trades with someone opening one: the contract changes hands and OI stays the same.
- A buyer and a writer both close: OI goes down by one.
That is why OI and volume differ. Volume counts every trade in the session. OI counts what is still open once those trades are done.
Reading OI in the sample chain
In the sample chain, total call OI is 13,11,460 contracts and total put OI is 11,35,910. The largest single figure on the call side is 1,48,630 at the 25,500 strike; on the put side it is 1,42,960 at 25,000. With spot at 25,180, the heaviest call OI sits 320 points above spot and the heaviest put OI 180 points below it.
Spot 25,180. The two largest positions are labelled.
- Call OI
- Put OI
Show the numbers
| Strike | Call OI | Put OI |
|---|---|---|
| 24,550 | 9,420 | 47,380 |
| 24,600 | 14,860 | 71,560 |
| 24,650 | 6,210 | 38,940 |
| 24,700 | 18,930 | 82,610 |
| 24,750 | 7,480 | 49,270 |
| 24,800 | 26,340 | 1,12,450 |
| 24,850 | 9,870 | 55,830 |
| 24,900 | 31,550 | 86,720 |
| 24,950 | 12,640 | 61,340 |
| 25,000 | 68,210 | 1,42,960 |
| 25,050 | 21,470 | 58,410 |
| 25,100 | 49,880 | 79,550 |
| 25,150 | 36,720 | 44,280 |
| 25,200 | 91,640 | 63,170 |
| 25,250 | 58,330 | 23,640 |
| 25,300 | 1,04,870 | 31,020 |
| 25,350 | 61,920 | 11,480 |
| 25,400 | 88,450 | 17,960 |
| 25,450 | 57,160 | 6,930 |
| 25,500 | 1,48,630 | 21,370 |
| 25,550 | 52,780 | 4,860 |
| 25,600 | 96,310 | 8,740 |
| 25,650 | 41,260 | 3,120 |
| 25,700 | 83,540 | 5,630 |
| 25,750 | 33,870 | 2,410 |
| 25,800 | 79,120 | 4,280 |
Many traders read a large block of call OI above spot as a level where call writers have positioned, and a large block of put OI below spot the same way for put writers. That reading describes where positions sit today. It is not a forecast: positions change every session, and OI does not show whether a writer or a buyer started a position.
What OI does not tell you
- Direction. Each contract has a buyer and a writer, so OI on its own is neutral. Pair it with the price change to see which side was more active: that is what OI buildup describes.
- Intent. Some positions are hedges against a portfolio, not views on where Nifty is going.
- Other expiries. A chain shows one expiry at a time. OI at the same strike in another expiry is a different set of contracts.
Platforms also differ in units: some show OI in contracts and some in units, which is contracts times the lot size. The reading is the same; only the scale changes.
Where to look next
OI is a level. How it moved today is in the next column, change in OI. Paired with the price change, that gives the four buildups, and adding OI up across every strike gives the put-call ratio.
Related lessons
- Change in OI: what positive and negative numbers mean
- Long buildup, short buildup, short covering and long unwinding
- PCR (put-call ratio) in the option chain
Open the sample chain to select any number and read what it means.
Educational content, not investment advice. Every figure here comes from a synthetic sample chain, not live prices. See the terms of use.