Understanding Open Interest: The term open interest (OI) is one of the most popular terminologies used among stock market traders. In this article, we are going to discuss what exactly is Open Interest. Here, we’ll discuss it’s definition, what does an increase or decrease in open interest implies, the difference between open interest vs volumes, and how one should interpret open interest. Let’s get started.

Open Interest Definition

Open Interest is the total number of the futures contracts (or Options) held by market participants at any given point of time. The total number of open interest contracts keeps on changing with every transaction executed. The open interest is said to be the best indicator to gauge the market sentiment and understand the reliability of the price movements.

Therefore, for an open interest to exist, there must be a buyer for every seller and vise-versa. Here, the relationship between buyer and seller creates one open interest. So, when buyers and sellers come together and initiate one new position, then open interest is increased by one unit. And when the same buyer and seller decrease their position, an open interest is reduced. But, if a buyer and seller passes their position to a new buyer and seller, then the Open interest remains unchanged, its just a transfer of position.

What does the Increase/Decrease in Open Interest Imply?

An increase in Open Interest means that new money is flowing in the market. And it generally indicates that the present trend (Bullish, Bearish, or sideways) is expected to continue.

A decline is an open interest usually implies, that the current trend is expected to halt and we could see a reversal in the market. To know the current open Interest, we just need to know the total from the buyer or seller side and not both.

Difference between Open Interest (OI) and Volumes

There is generally a common misconception that both OI and volumes mean one and the same thing. However, they are two different concepts, giving out two different sets of data. But, both the data can be used in conjuncture. Let us understand the concept of Open Interest with the help of an example.

Say, there are five traders (A, B, C, D, E) trading the Nifty futures contract. Let us understand, as to how their trading has an impact on the open interest and its calculation.

On Monday: ‘A’ buys 20 Nifty futures contract and ‘B’ also buys 10 Nifty futures contract. While ‘C’ sells 30 Nifty futures contract in the market. Therefore, we have a buying activity of 30 futures contracts and a selling activity of 30 futures contracts. Hence, the total Open Interest is 30.

Trader	Buy (L = Long)	Sell (S = Short)	Contract held
A	20		20L
B	10		10L
C		30	30S
D
E
Total			30

On Tuesday: C wants to get rid of half the position and ‘D’ comes into the market and takes 15 short contacts from C. Here just the mere transfer of position happened and no new contracts were added. So, the open Interest will still stand at 30.

Trader	Buy (L = Long)	Sell (S = Short)	Contract held
A
B
C	15		15L
D		15	15S
E
Total			30

On Wednesday: D wants to add 15 more short contracts. And both A & B want to add 5 long contracts each, to their existing long positions. And C wants to exit 5 more short contract position form here existing position of 15 short contracts. Therefore, 10 more long contracts (both A & B) are added in the market. And the contract between C and D would be just a mere transfer of positions. In short, the table on Wednesday would look like this:

Trader	Buy (L = Long)	Sell (S = Short)	Contract held
A	5		5L
B	5		5L
C	5		5L
D		15	15S
E
Total			30

On Thursday: Trader E decides to enter the market. And wants to sell 50 Nifty futures contracts. Therefore, trader D decides to exit his 30 lots position and transfers his position to E. While trader A & B add position so 10 lots each to their existing positions. Overall, 20 new lots get added to the system and the final table at the end of Thursday looks like:

Trader	L	S	Contracts	L	S	Contracts	L	S	Contracts	L	S	Contracts
A	20		20L			20L	5		25L	10		35L
B	10		10L			10L	5		15L	10		25L
C		30	30S	15		15S	5		10S			10S
D					15	15S		15	30S	30		0
E											50	50S

If we carefully analyze and look at the table above, it gives us a fair sense that open interest is eventually a zero-sum game. If we add all the longs and subtract them with all the shorts in the market. The end result is eventually zero.

Figure 1: Open Interest data (Moneycontrol.com)

Now, if we look at the snapshot above (Fig 1), it is the data showing the shares with the highest change in the open interest for the day. With the change in the open interest, the share price has also gone up and which is usually an indication that the buying momentum is expected to continue in these ten shares.

— Open Interest and Volume interpretation

From the discussion above it is clear that OI tells us information about the contract which are open and live in the market. But, the volume gives us information about the number of trades executed in the market.

The volume data is reset at the end of the day and the new counter starts at the beginning of the next day, but the data of the OI is a continuation from the previous day. 10 lots bought and 10 lots amount to 10 volume and 10 OI for the day.

— Interpreting Open Interest

Price	Open Interest (OI)	Expectation from market
Increase	Increase	The buying momentum is most likely expected to continue
Decrease	Decrease	Long unwinding can be seen i.e., buyers are exiting from the market
Increase	Decrease	Short covering can be seen in the market.
Decrease	Increase	We could be a reversal in buying momentum as we can see more shorts than longs in the Market.

Conclusion

In this article, we tried to simplify the concept of open interest in share market and what it interprets. Here are a few of the top takeaways from this post:

• Open interest gives you information about the total number of contracts which are outstanding in the market.
• It is an excellent indicator to understand the market sentiment and expected momentum in the market.
• When the contract switches hands, it’s just a transfer of positions and Open interest does not change.
• The data of volume refreshes every day but Open Interest is a continuous data.

That’s all for this post. I hope it was useful for you. If you still have any queries related to open interest in the share market, please comment below. I’ll be glad to help you out. Happy trading.