Open interest is the number of futures or options contracts that are still open in the market at the end of a session. Traders read it next to price to judge whether new money is entering a move or old positions are closing. This guide explains how it works, how to read it with price and options data, and where to find official figures.
Key Takeaways
- OI counts contracts that are still open, so it rises only when new positions are created.
- Volume resets every day, while OI carries forward from one session to the next.
- Read OI with price: rising price with rising OI is a long build-up, and falling price with rising OI is a short build-up.
- In options, compare call and put OI by strike and watch the put call ratio, but never treat one level as a signal.
- Official daily figures come from NSE after the market closes, and this guide is educational, not advice.
In this guide:
- What is open interest and why traders watch it
- How OI goes up and down
- Price and OI: the four combinations
- OI in options and the put call ratio
- Worked example over five days
- Where to find official OI data
- Common mistakes
- Pros and cons of open interest
- FAQ
- The bottom line
What Is Open Interest and Why Traders Watch It
Every futures or options contract has two sides, a buyer and a seller. Open interest, often written as OI, counts the contracts that have been opened and not yet closed, expired or settled. Each contract is counted once, not twice. If OI is 10, there are 10 long positions and 10 matching short positions.
Why does it matter? Price tells you where the market traded. OI tells you how many positions are still riding on that price. A move backed by growing OI means fresh positions are being added. A move with falling OI usually means traders are closing what they already hold. That context is useful, but it never predicts the next move on its own.
Open Interest vs Volume
Volume counts every contract traded during the day. Open interest counts the contracts still open when the day ends. A trader who buys and sells the same contract within minutes adds to volume but leaves OI unchanged, because no position is left open.
| Feature | Volume | Open interest |
|---|---|---|
| What it counts | Contracts traded in a session | Contracts still open |
| Resets each day? | Yes | No, it carries forward |
| What it shows | Activity and liquidity | Positions still held |
| Changes when | Any trade happens | A position is created or closed |
A Simple Way to Remember the Difference in Open Interest
Think of a shop. Volume is the footfall during the day, everyone who walked in and out. Open interest is the number of customers still inside at closing time. Footfall can be huge while the shop is nearly empty by evening.
How OI Goes Up and Down
OI changes only when a trade creates or closes a position. Three cases cover every trade. If both sides are opening new positions, OI rises. If one side opens and the other closes, the position simply changes hands and OI stays the same. If both sides are closing, OI falls.
| Trade type | Buyer | Seller | Effect on OI |
|---|---|---|---|
| Both sides new | Opens a long | Opens a short | OI rises |
| One new, one closing | Opens a long | Closes an old long | OI unchanged |
| Both sides closing | Closes a short | Closes a long | OI falls |
Why OI Stays Flat When Positions Change Hands
Suppose Trader B is short 200 contracts and wants out. Trader C wants a fresh short position of 200 contracts. B buys back to close, and C sells to open. One side closes and one side opens, so the count of open contracts does not move. Heavy trading with flat OI often means positions are being passed around rather than added.
Open Interest and Price: The Four Combinations
OI on its own says little. Pair it with the price change over the same period and you get four common readings. Each one describes who is likely entering or leaving the market, and each is a tendency, not a rule.
| Price | OI | Common name | What it often suggests |
|---|---|---|---|
| Up | Up | Long build-up | New buyers are entering |
| Down | Up | Short build-up | New sellers are entering |
| Up | Down | Short covering | Sellers are closing positions |
| Down | Down | Long unwinding | Buyers are exiting |
Reading Open Interest When Price Rises
Rising price with rising OI points to fresh buying, because new long positions are being added. Rising price with falling OI usually means short sellers are buying back to close. That second kind of rally has no new buyers behind it, so some traders treat it with more caution. It is still only a pattern.
Reading OI When Price Falls
Falling price with rising OI points to fresh selling. Falling price with falling OI means long holders are leaving. Zerodha Varsity also warns that unusually high OI together with sharp price moves points to crowded positions, where a small trigger can cause panic. When many traders hold the same side, an exit by a few can move the price quickly.
Open Interest in Options and the Put Call Ratio
Options have OI too. It is counted separately for each strike price and for calls and puts, so one index can show hundreds of OI figures on a single day. Traders scan these figures to see where positions are crowded.
How to Read Call and Put OI by Strike
A strike with very large call OI is a level where many call contracts are open. A strike with large put OI is the same for puts. OI does not say whether the larger share belongs to buyers or to option writers, and the two groups hope for opposite outcomes. So treat strike-wise OI as a map of where positions are crowded, not as a forecast of where the index will stop.
Put Call Ratio and Open Interest
The put call ratio (PCR) divides total put OI by total call OI. Suppose an index has 24,00,000 put contracts open and 18,00,000 call contracts open. The PCR is 24,00,000 divided by 18,00,000, which is 1.33. A ratio above 1 means more puts than calls are open. What that implies for the market is debated, and levels that look high or low change over time. Use PCR as one input next to price. You can find short definitions of PCR and similar terms in our FII DII glossary.
Worked Example: Reading Open Interest Over Five Days
All numbers below are hypothetical and chosen to show the method. They are not real market data. We start with how OI is counted, then pair OI with price.
Step 1: Count OI Day by Day
Suppose a new futures contract starts trading. Here is what happens in its first week.
| Day | What happens | Change in OI | OI at close |
|---|---|---|---|
| Mon | Trader A buys 600 contracts from Trader B. Both open new positions. | +600 | 600 |
| Tue | B buys back 200 contracts from Trader C, who sells to open. One side closes, one opens. | 0 | 600 |
| Wed | 300 new contracts are created between two new traders. | +300 | 900 |
| Thu | Traders on both sides close 150 contracts. | -150 | 750 |
| Fri | 250 new contracts are created and 100 are closed on both sides. | +150 | 900 |
The arithmetic is simple. Monday: 600. Tuesday: 600 plus 0 is 600. Wednesday: 600 plus 300 is 900. Thursday: 900 minus 150 is 750. Friday: 750 plus 250 minus 100 is 900. Notice that Tuesday had trading but no change in OI.
Step 2: Pair OI With Price
Now suppose an index future closes at 22,000 on day 1 with OI of 1,00,000 contracts. Over the next four days it moves as follows.
| Day | Close | Price change | OI | OI change | Reading |
|---|---|---|---|---|---|
| 2 | 22,220 | +1.00% | 1,08,000 | +8.00% | Long build-up |
| 3 | 22,110 | -0.50% | 1,03,500 | -4.17% | Long unwinding |
| 4 | 21,890 | -1.00% | 1,11,000 | +7.25% | Short build-up |
| 5 | 22,000 | +0.50% | 1,04,400 | -5.95% | Short covering |
Check day 2: price rose by (22,220 minus 22,000) divided by 22,000, which is 1.00%. OI rose by (1,08,000 minus 1,00,000) divided by 1,00,000, which is 8.00%. Price up and OI up gives a long build-up. On day 4, price fell by about 1.00% while OI rose 7.25%, so new sellers appeared. By day 5 the price is back at 22,000, the same as day 1, yet OI is 4.4% higher (4,400 divided by 1,00,000). Price alone would have hidden that extra positioning.
Where to Find Official OI Data
NSE publishes derivatives data for each trading day, including OI for futures and options, on its website after the market closes. Report names and release times may vary; check the official site for the current list. Your broker platform also shows intraday OI, though its refresh rate depends on the platform.
To see who holds the positions, use our page of participant wise open interest data, which splits OI across FII, DII, Pro and Client. Our FII DII F&O data page shows the daily change, and our FII and DII data home page links to every daily dataset. Official figures are released after the close. If the NSE file is new to you, the participant wise OI meaning guide walks through it, and the guide on Pro and Client positioning explains the biggest gap in that file.
SEBI has also changed how position limits count OI. If you want that background, read how SEBI now counts positions for limits and confirm the current rules on the SEBI website.
A Five-Step Daily Routine for OI
- Note the day’s price change in the contract you follow.
- Open the OI figure for the same contract and compare it with the previous day.
- Name the combination using the four-way table above.
- For options, list the strikes with the largest call and put OI and check whether they changed.
- Compare with participant wise data to see which group added or cut positions.
Common Mistakes When Reading OI
- Calling rising OI bullish by default. Rising OI only says new positions are being created. Direction comes from price.
- Ignoring expiry effects. Near expiry, OI in the current contract falls as traders close or roll to the next one, while OI in the next contract rises. A fall near expiry may say nothing about direction.
- Judging from one day. One session can be noise. Look at several sessions before naming a trend.
- Forgetting who holds the positions. The same OI can come from hedgers, arbitrage desks or directional traders, and they act differently.
- Treating a pattern as a signal. A long build-up does not promise a rally. Patterns describe what happened, not what comes next.
Pros and Cons of Open Interest
| Pros | Cons |
|---|---|
| Shows whether new positions are entering or old ones are leaving | Does not show whether buyers or sellers are the more aggressive side |
| Published by the exchange for each trading day | Can mislead near expiry because of closing and rollover |
| Adds context to price and volume | Official end-of-day data arrives after the session closes |
| Works for index and stock futures and options | Patterns are tendencies, not rules |
| Helps spot crowded positioning | Very high OI can mean crowded risk, and sharp reversals can follow |
Frequently Asked Questions
What is open interest in simple words?
Open interest is the number of futures or options contracts that are still open and not yet closed, expired or settled. Each contract is counted once, even though it has a buyer and a seller.
Is high OI good or bad?
Neither by itself. High OI means many positions are open, which usually goes with good liquidity. It can also mean crowded positions, so check price direction and who holds the contracts before drawing a view.
What does rising OI with rising price mean?
It is called a long build-up. Price is going up while new positions are being added, which often means fresh buyers are entering. It is a pattern, not a guarantee that the rise will continue.
How is OI different from volume?
Volume counts all contracts traded in a session and resets each day. Open interest counts contracts still open at the end of the session and carries forward to the next day.
Where can I check open interest data for Nifty?
NSE publishes derivatives data after the market closes, and broker platforms show intraday figures. For participant-wise splits, see the NSE participant wise open interest page on this site. Report names and timings may vary; check the official site.
The Bottom Line
Open interest is a simple count of contracts that are still open, yet it answers a question price cannot: are traders adding positions or leaving them? Paired with price, it gives four readings, long build-up, short build-up, short covering and long unwinding. Paired with strike-wise data, it shows where options positions are crowded.
Use it as context, not as a trigger. It changes with expiry, it does not say who is right, and a pattern that worked last week may not work next week. For more guides like this, browse the FII DII blog.
Your next step: pick one contract, write down the price change and the OI change for five sessions, and name the combination each day before reading any forecast.
Sources: Zerodha Varsity, Open Interest chapter; NSE India; SEBI. Worked example numbers are hypothetical.
Disclaimer: This article is for educational purposes only and is not investment advice. Please consult a SEBI-registered advisor before making investment decisions.
