Between Monday 15 Jun and Tuesday 30 Jun 2026 the open interest of the June Nifty future fell on every session until about a quarter was left. Read alone, that looks like longs giving up, or shorts covering. Now look at the July future over the same days: its open interest climbed as steadily as June's fell. Same traders, new contract. I check which contract a number belongs to before I read anything into a fall in open interest. This lesson covers what open interest counts, how it differs from volume, and the four patterns that screens print from the two. Every figure comes from NSE end of day files and is dated, not live.

3By the end you can

  1. Say what open interest, change in OI and volume each count, and convert units to contracts.
  2. Name the four build up patterns from the price move and the OI move.
  3. Explain why a fall in the near month's OI can be a roll and not an exit.
The RupeeCase terminal on sample data: Order status: what do Placed, Open and Partly filled mean?
Watch in the terminal: what do Placed, Open and Partly filled mean? A short tutorial on sample data.

The idea, plainly

Open interest, or OI, counts the contracts that are still open. Every contract has one buyer and one seller, and the pair counts once. A new buyer meeting a new seller adds one contract. An old buyer and an old seller closing against each other remove one. If one side opens while the other closes, the count does not move.

One trade moves open interest up, leaves it alone, or moves it down

A trade changes open interest by one contract up, by none, or by one contract down, depending on whether the buyer and the seller are opening or closingDiagram with 4 boxes. A trade is struck to Both sides open; A trade is struck to One opens, one closes; A trade is struck to Both sides close.A trade is struckBoth sidesopenOI up by onecontractOne opens,one closesOI unchangedBoth sidescloseOI down byone contract
What counts is whether each side is opening a position or closing one. The count says nothing about which side was right. Source: RupeeCase illustration of how NSE counts open interest. As of 16 Oct 2026.
Read 2 more paragraphs, 129 words

Volume counts the contracts traded in the day, whatever they did to OI. Think of a car park. Volume is the cars that drove through. Open interest is the cars still parked at night. A day trader who buys and sells the same contract all day adds to volume with every trade and leaves nothing open at the close.

Mind the unit. NSE's end of day file counts open interest in units, so each contract adds 65. Many screens count contracts. Volume is in contracts. Convert before you compare. Change in OI is today's OI less yesterday's. Cumulative OI is the OI of every expiry month added together, which on a futures screen means the three monthly contracts. The short answer is on the open interest question page.

The four build up patterns

Screens combine two numbers, the day's price move and the day's change in OI, into four labels.

OI risesOI falls
Price risesLong build upShort covering
Price fallsShort build upLong unwinding
  • The roll. The near month's OI falls into expiry mostly because positions move to the next month, not because anyone gave up.
  • Hedges and arbitrage. A fund that holds shares and sells futures against them adds to OI, and on a day the price falls that prints as a short build up, with no view on the index at all.
  • Size. A rise of a few points earns the same label as a rise of a few hundred. The label records the sign of each number, not how large it was.
  • Both sides. Every new contract has a seller as well as a buyer. Price is read as showing which side was keener to trade. OI cannot say who is right.
Read one more paragraph, 75 words

Each label is a story told from the direction of price. Price up with OI up is read as new buyers. Price down with OI up, as new sellers. Price up with OI down, as sellers closing. Price down with OI down, as buyers closing. The labels describe the day. They are not signals for the next one, and four things can break even the description. The build up question page has the short version.

Worked example: June 2026 and the eve of expiry

First the roll. The June future's open interest, in units, at each close from 15 Jun to expiry day, 30 Jun:

The June future's open interest fell on every session into expiry

Open interest of the June Nifty future in units at each close from 15 Jun to 30 Jun 2026: it falls on every session until about a quarter is leftNifty rollover: from 1,78,17,930 at 15 Jun 2026 to 47,80,620 at 30 Jun 2026, high 1,78,17,930 at 15 Jun 2026, low 47,80,620 at 30 Jun 2026.50L75L1Cr1.25Cr1.5Cr1.75Cr15 Jun18 Jun21 Jun24 Jun27 Jun47.8L
Near month Nifty future, open interest in units, from 15 Jun to expiry day on 30 Jun 2026. Divide by 65 for contracts. L is lakh and Cr is crore. Source: NSE end of day data, computed by RupeeCase. As of 30 Jun 2026.

Now the same window for the July future.

The July future's open interest rose on every one of the same sessions

Open interest of the July Nifty future in units at each close from 15 Jun to 30 Jun 2026: it rises on every sessionNifty rollover: from 19,10,350 at 15 Jun 2026 to 1,79,38,180 at 30 Jun 2026, high 1,79,38,180 at 30 Jun 2026, low 19,10,350 at 15 Jun 2026.50L1Cr1.5Cr2Cr15 Jun18 Jun21 Jun24 Jun27 Jun1.79Cr
Next month Nifty future, open interest in units, over the same sessions. What June lost, July gained. Source: NSE end of day data, computed by RupeeCase. As of 30 Jun 2026.

On expiry eve the strikes near the money traded many times their open interest

Show all columnsShow fewer columns
Option chain for Nifty, 30 Jun 2026 expiry: 11 strikes around the at the money strike 23,950.
CallsCallsStrikePutsPuts
OIVolumeVolumeOI
4.8L94,49323,70030.6L71.8L
2.6L71,27123,75025.2L42.1L
21.3L5.2L23,80051.4L1.06Cr
9.2L4.7L23,85040.6L41.9L
33.4L21.6L23,90080L92L
Spot 23,946.25Spot 23,946.25
51L37.3L23,950ATM72.3L55.9L
1.72Cr77.8L24,0001.03Cr1.2Cr
67.1L57.2L24,05057.8L22.4L
1.57Cr95L24,10060.8L49.4L
70.8L48.7L24,15017.3L8.2L
1.38Cr54.7L24,20015.3L27.2L

Shaded cells are in the money. Outlined cells hold the most open interest among the strikes shown. OI is in units and volume is in contracts; L is lakh and Cr is crore.

Calls on the left, puts on the right, the strike in the middle, for the Nifty chain of 29 Jun 2026. Volume is in contracts and open interest in units, so divide the OI by 65 before comparing. Source: NSE end of day data, computed by RupeeCase. As of 29 Jun 2026.
Read 4 more paragraphs, 237 words

A screen that shows only the near month would label every one of those June days long unwinding or short covering, according to the day's price move. Over the same days the next month was filling up. Whoever looked only at June saw a market emptying out. Whoever added July saw positions moving house. Module F10 follows that move and what it costs.

Now volume against OI, on the chain of Monday 29 Jun 2026, the eve of expiry. Take the 24,100 call. It traded 94,99,236 contracts that day. At the close 1,57,43,650 units were open, which is 2,42,210 contracts at 65 units each. Volume was 39.2 times the open count. The open count itself had grown by 1,21,811 contracts, from 1,20,399 the day before, so it roughly doubled and was still a small fraction of the day's traffic.

Try the arithmetic on the table. Pick any strike, divide its OI in units by 65 to get contracts, then divide the volume by those contracts. That is the turnover ratio. Do it again for a strike further from the money and compare the two.

So which one matters? Volume tells you how busy a strike was, which is liquidity. OI tells you how much is still open and has to be closed or settled. Neither tells you direction. The question page takes that one to its short answer, and module F18 reads OI across a whole chain.

3 terms this section turns on

3 terms this section turns on3 terms this section turns on. Open interest: The number of contracts still open at the close, counted once for each buyer and seller pair. Volume: The number of contracts traded during the day, whatever they did to open interest. Short covering: Price up and open interest down. Read as sellers buying back to close.Open interestThe number of contracts still open at theclose, counted once for each buyer and sellerpair.VolumeThe number of contracts traded during the day,whatever they did to open interest.Short coveringPrice up and open interest down. Read assellers buying back to close.
From the module glossary; every term is in the Learn glossary too. Source: Module 13.3, Open interest, volume and the four build up patterns.

The common mistake

The belief: Open interest is rising, so the big players are buying. Look at what rose. On the 24,100 call, OI roughly doubled in a day, and every one of those new contracts has a buyer and a seller. OI can tell you that positions were opened. It cannot tell you which side opened them with a view, which side was hedging shares, or which side will close by lunch. Price direction is doing all the work in the four labels, and open interest only decides which pair of labels you get. Treat a build up as a description of the day and check the contract month before you believe it.

Key takeaways

  • Open interest counts contracts still open. Volume counts contracts traded in the day.
  • NSE's day file counts OI in units. Divide by the lot of 65.
  • OI changes only when both sides open or both sides close.
  • The four labels describe the day. They do not signal the next one.
  • Near month OI drains into expiry because positions roll to the next month.
  • Hedges and arbitrage count as build ups with no view on the index.
The RupeeCase terminal on sample data: Return distribution: what do skew and kurtosis say?
Watch in the terminal: what do skew and kurtosis say? A short tutorial on sample data.

Before you trade. Derivatives trading carries a high risk of loss. SEBI's study "Profitability of Individual Traders in the Equity Derivatives Segment (FY25 to FY26)" (August 2026) found that 87.7% of individual traders in equity F&O made net losses in FY26, with aggregate net losses of Rs 91,685 crore. Read the SEBI study