Open interest is the total number of open contracts that have not been closed or settled. If you want to know how many positions are still alive in a futures or options market, this is the number to check.
Many traders watch price and ignore it. That leaves out useful information, because open interest shows how much money is committed behind a move. This guide covers how it works, how to read it, and where it fits in a trading plan.
1. What Is Open Interest and How Does It Work?
So, what is open interest in practice? Every futures or options contract has a buyer on one side and a seller on the other. Open interest counts that contract once, not twice, so a trade between one new buyer and one new seller adds a single contract to the total.
A simple example shows how it moves:
Trader A buys 10 contracts from Trader B, who sells 10. Both are opening new positions, so open interest rises by 10.
Trader A then sells 5 of those contracts to Trader C, a new buyer. Open interest stays at 10, because the position only changed hands.
Finally, Trader B buys back all 10 short contracts from the two long holders, who sell out. Every position is now closed, so open interest falls by 10.
In short, open interest goes up when a new buyer and a new seller open a contract, and it goes down when both close. It stays flat when one trader replaces another. Exchanges work it out at the end of each session by adding up all outstanding contracts, so it updates once a day, not tick by tick.
2. Open Interest vs. Volume: What Is the Difference?
Volume counts every contract traded during a session, including those opened and closed on the same day. Open interest is a snapshot of what is still open when the session ends. A day trader who buys 100 contracts and sells them before the close adds to volume but leaves open interest unchanged.
A useful way to think about it: volume measures activity, while open interest measures commitment. High volume with flat open interest often means a lot of short term churn. Rising open interest means fresh money is entering the market.
The real value comes from reading price and open interest together. The table below shows the four combinations and what each usually suggests.
Price Open interest What it usually suggests
Up Up New money is entering long positions, so the uptrend has support
Up Down Short sellers are covering, so the rally may lack conviction
Down Up New short positions are being added, so the downtrend has support
Down Down Longs are exiting, so selling pressure may be fading
Treat these as tendencies, not rules. They tell you who is probably driving the move, not where it ends.
3. Open Interest in Options: How to Read It
If you are asking what is open interest in options, the answer is the number of option contracts at a given strike and expiry that are still outstanding, meaning they have not been exercised, closed or allowed to expire. An option chain lists this figure for every strike, for both calls and puts.
Here is how traders usually read it:
High call open interest at a strike. Many traders have sold calls there, and the level is often treated as resistance.
High put open interest at a strike. Many traders have sold puts there, and the level is often treated as support.
Change in open interest. The daily change matters more than the absolute level. Rising open interest alongside rising premium usually points to fresh buying. Rising open interest with falling premium often points to fresh writing.
One limit to keep in mind: open interest does not tell you whether a given contract was bought or written by a particular trader. It shows that positions exist, not who holds which side. Our Option Chain Analysis and Options Trading guides go deeper on strike selection and strategy.
4. How to Read an Open Interest Chart
An open interest chart usually plots open interest as a line or histogram beneath the price chart, so you can compare the two over the same period. The method is the same on any chart, so here is an annotated walkthrough you can apply to any market.
Picture price moving through four phases, with open interest plotted below:
Point Price action Open interest Reading
A Breaks above a range Rising Fresh longs are joining, so the breakout has backing
B Keeps climbing Flat The trend continues, but new participation has slowed
C Pulls back Falling Longs are taking profit, so this looks like an exit, not fresh selling
D Breaks below support Rising sharply New shorts are entering, so the breakdown has conviction
A few habits make the chart more reliable:
Compare the same contract. Open interest moves from the near month to the next month around expiry, so a sudden drop in an expiring contract is not necessarily bearish.
Look for divergence. Price making new highs while open interest falls is a warning that fewer traders are backing the move.
Use it with your usual tools. Our Futures Trading and Technical Analysis guides explain how to combine open interest with trend and support and resistance.
5. Participant Wise Open Interest: What FII, DII, Pro, and Client Positions Tell You
Participant wise open interest splits the market by who holds the positions. The NSE publishes this data after market close each trading day, covering index futures, stock futures, index options and stock options. It groups traders into four categories:
Client: individual and other non institutional traders
DII: domestic institutions such as mutual funds and insurers
FII: foreign institutional investors
Pro: proprietary traders and broker own accounts
For each group, the data shows contracts held long and short. Here is a worked example using made up numbers for index futures:
FII long: 90,000 contracts
FII short: 1,50,000 contracts
Net position: 90,000 minus 1,50,000 equals 60,000 net short
Suppose the previous day showed a net short of 40,000. FIIs added 20,000 net shorts, so their futures positioning is turning more cautious. Next, check the other groups. Because every contract has a counterparty, net positions across all four categories add up to zero, so a growing FII net short will be matched by net long positions elsewhere, often in the Client category.
Two cautions apply. The trend in net positions over several sessions tells you more than a single day. And a net short in futures does not always mean a bearish view, since institutions often use futures to hedge cash holdings or options positions.
6. Nifty Open Interest: How to Use It in Trading
Nifty open interest is one of the most watched figures in Indian markets, because it covers both Nifty futures and Nifty options. A simple routine keeps the analysis structured:
Check futures. Compare price with Nifty futures open interest using the four combinations in the table above.
Mark the option zones. Find the strikes with the highest call and put open interest on the option chain. These often frame the range traders expect.
Watch the changes. See where open interest is being added or removed, especially in the days before expiry.
Add participant data. Check whether FII and other groups are building or reducing positions.
Confirm with price. Wait for price action and volume to agree before acting.
The last step matters most. Open interest shows positioning, not direction on its own. A heavy put base can fail, and a call wall can break. Use it to understand who is in the market and how committed they are, then let price action and volume confirm the trade. Always size positions with a stop loss in mind.
7. Frequently Asked Questions About Open Interest
What does an increase in open interest mean?
It means new contracts are being opened faster than old ones are closed, so more money is entering the market. If price is rising at the same time, it usually supports the trend. If price is falling, it usually supports the downtrend.
Is high open interest bullish or bearish?
Neither on its own. High open interest means many positions are open, but it does not say which side is winning. Read it alongside price direction and volume before drawing a conclusion.
What is the difference between open interest and volume?
Volume counts all contracts traded in a session, including those opened and closed the same day. Open interest counts only the contracts still open at the end of the session.
How is open interest calculated?
The exchange adds up all outstanding contracts at the end of each trading day. A new buyer and a new seller increase it, closing trades reduce it, and a position simply changing hands leaves it unchanged.
How do you use open interest in options trading?
Compare open interest across strikes to spot likely support and resistance, and track daily changes to see where positions are being added. Then confirm with price action, premium movement and volume before placing a trade.
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