What is
Open Interest?
Open interest is the clearest signal of where real money is committed in the options market. Here's what it means, how to read change in OI, and how it reveals support and resistance.
Open interest, defined
Open interest (OI) is the total number of option contracts at a given strike and expiry that are currently open — created but not yet closed out, exercised or expired. Every contract has a buyer and a seller; one new contract between a fresh buyer and a fresh seller adds 1 to OI.
OI rises when new positions are opened and falls when existing positions are closed. That makes it a running measure of commitment in the market, unlike volume, which only measures the day's activity.
Open interest vs volume
- Volume = contracts traded today. Resets to zero each session.
- Open interest = contracts still open. Carries over day to day.
A strike can have huge volume but little change in OI (day traders opening and closing), or modest volume with a big OI jump (positions being held). Reading them together tells you whether activity is genuine positioning or just churn.
Change in OI — the real signal
The single most useful field is change in OI. Combined with the price move, it classifies what traders are doing:
- Long buildup — price up, OI up → fresh buyers (bullish).
- Short buildup — price down, OI up → fresh sellers (bearish).
- Short covering — price up, OI down → sellers exiting (bullish, often sharp).
- Long unwinding — price down, OI down → buyers exiting (bearish).
Support & resistance from OI
Option writers defend the strikes where they've sold, so OI concentrations act like walls. The highest call OI strike tends to act as resistance; the highest put OI strike tends to act as support. Watch for these walls to shift — when heavy OI unwinds at a level, that level is likely to break.
Watch OI move in real time
TradePulse shows live OI and change in OI across every NIFTY and Bank Nifty strike, with AI commentary on the buildup.