Price tells you where the market is. Open interest tells you where the market is positioned, and positions are harder to fake than prices. That is why open interest analysis is usually the first check an F&O trader makes.
What is open interest?
Open interest is the total number of outstanding options contracts, calls or puts, that have been opened but not yet settled or squared off. Every unit of OI represents a live commitment, a buyer and a seller with money on the line at that strike.
Open interest versus volume
The two are often confused and they measure different things.
Volume counts every trade and resets to zero each day. It measures activity.
Open interest carries over from one day to the next and rises only when new positions are created. It measures how much conviction is parked at a level.
This distinction matters because a strike can show heavy volume while OI falls, which means positions are being closed rather than opened. The activity suggests interest arriving; the OI tells you it is leaving.
Why open interest indicates support and resistance
Institutions and large funds are typically option sellers, and a seller loses money when price moves through the strike they have written. A writer of calls at a given strike is exposed above it, which gives them a direct interest in defending that level. The larger the Call OI at a strike, the more capital is committed to holding price below it.
The same logic in reverse makes strikes with large Put OI act as floors. As an analytical observation, the strike carrying the highest Put OI tends to act as support and the strike carrying the highest Call OI tends to act as resistance.
The two charts in the OI widget
The Open Interest widget on IBT-ProTrade stacks two charts, and the pair tells you more than either alone. Red bars show Call OI, green bars show Put OI, and a dashed line marks the current spot level.
Total open interest shows all outstanding contracts at each strike for the selected expiry. This is where the established walls stand.
Today's OI change shows only what moved today, meaning where fresh positions were added or existing ones unwound. New walls carry more weight than old ones, which is why intraday traders work mainly from this second chart.
The OI and price cheat sheet
| What you see | What it indicates |
|---|---|
| High Put OI at lower strikes | Support zone, put writers defending it |
| High Call OI at higher strikes | Resistance zone, call writers defending it |
| OI rising with price rising | Long buildup, fresh buying behind the move |
| OI rising with price falling | Short buildup, fresh selling pressure |
| OI falling with price rising | Short covering, the rally may lack fresh conviction |
| OI falling with price falling | Long unwinding, existing longs exiting |
| Sudden OI buildup at a new strike | A new range may be forming, worth watching |
| Call and Put OI both heavy at one strike | Consolidation or pinning zone around that level |
Using the widget
Switch instruments with one tap across the major indices, or use Search Scrips for stock F&O. Pick your expiry, noting that indices carry weekly expiries while stocks are monthly. Toggle Call OI, Call OI Change, Put OI and Put OI Change individually to declutter the view, and switch between Chart and Table when you want exact figures rather than bars. Everything updates live during market hours.
A three step routine
Step 1. On the total OI chart, mark the highest Put OI strike and the highest Call OI strike. That pair frames the range the market is currently positioned for.
Step 2. On the OI change chart, check where fresh positions went today. Newly built walls carry more weight than older ones.
Step 3. Read it against price. Rising OI supports the prevailing move, falling OI raises questions about it. Treat a wall that breaks while OI unwinds as a genuine change rather than noise.
Go deeper. The Open Interest widget shows the walls. The Option Chain gives strike by strike detail including premiums and Greeks, Multistrike OI tracks chosen strikes through the day, and Max Pain distils the same OI data into a single expiry level.
