Open interest is the number of derivative contracts that are still open at a strike — neither closed out nor expired. Change in OI is the difference between that count now and the same count at the last close. Both are counts of contracts, not of rupees.
Definition and Formula
Every open contract has two sides. One party has bought it and another has written it, and the pair counts as one unit of open interest. When both sides close their positions, the count falls by one. When a fresh pair opens, it rises by one.
This makes open interest quite different from volume. Volume counts every contract that changed hands during the session, including contracts that were opened and closed on the same day. Those add to volume and leave open interest exactly where it was.
Change in OI is measured against the last close. The figure grows through the session and is fixed only once the session ends. A number read at eleven in the morning is one measurement. The same number read at three in the afternoon is another, of the same day.
The count is of contracts, not rupees. A strike on a large lot instrument cannot be compared with a strike on a small lot one by open interest alone. Multiplying by the lot size gives the number of underlying units, which is the comparable figure.
Exchanges also cap how much open interest a single participant may hold, and those caps are set per instrument. That is a rule about position size, not about the count itself. But it explains why the figure at some strikes stops growing while trading in them continues.
One further point about reading a change figure: it is a net number. A strike where two thousand contracts were closed and two thousand fresh ones opened shows a change of zero. Four thousand contracts moved even though the change reads zero. The change column and the volume column are answering different questions about the same strike.
Formula: Change in OI = open interest now − open interest at the last close · Underlying units = open interest × lot size
A Worked Example
| Call OI change at 24,200 / 24,300 / 24,400 | +1.80 L · +6.40 L · −1.20 L |
|---|---|
| Put OI change at 24,200 / 24,300 / 24,400 | +3.90 L · +2.10 L · −0.80 L |
| Largest call addition — strike | 24,300.00 |
|---|---|
| Largest call addition — contracts | 6,40,000.00 |
| Largest put addition — strike | 24,200.00 |
| Largest put addition — contracts | 3,90,000.00 |
| Total call OI in the chain | 50,30,000.00 |
| Total put OI in the chain | 51,10,000.00 |
The ranking and the totals are computed by the same code that builds the option chain pages on this site.
What This Number Tells You
Open interest states how many contracts stand open at a strike at this moment. Change in OI states how that count has moved since the last close.
A negative change states that more contracts were closed than opened at that strike during the session. A positive one states the reverse.
And What It Does Not Tell You
Neither figure states who is on which side. Every open contract has a buyer and a writer, and the count treats the pair as one.
Neither figure states why the contracts were opened. A position may be a hedge against something the chain cannot see, and the chain records only that the contract exists.
A large addition at one strike is not a statement about where the price will settle. It is a count of contracts opened, and nothing in a count carries a direction.
Frequently Asked Questions
Can open interest be higher than volume?
Yes, and often is. Open interest carries forward from earlier sessions, while volume counts only the current session. A strike with a large standing position can see very little trading on a given day.
What does a fall in open interest mean?
It means more contracts at that strike were closed during the session than were newly opened. It is a count of what happened, and it carries no direction of its own.
Is change in OI measured in contracts or shares?
In contracts. Multiplying by the lot size converts it to underlying units, which is what makes two instruments with different lot sizes comparable.
When is the figure final?
At the end of the session. Through the day it is a running measurement against the last close, so the same strike reads differently at different hours.
Why can change in OI be zero on an active strike?
Because the change is a net figure. If as many contracts were closed as were opened, the count ends where it started. A great deal of trading can still take place even so. Volume records that trading; change in OI does not.