Change in OI (COI)

Change in OI, often abbreviated COI, is simply the difference between a contract’s open interest at two points in time — usually today’s OI compared with the previous session’s closing OI, or the day’s opening OI compared with the current intraday reading. Where open interest is a snapshot — the total number of contracts currently outstanding — change in OI is the flow: it tells you whether that total is growing, shrinking, or flat over the period you’re measuring.

COI is the metric that actually powers the four buildup and unwinding patterns traders rely on. A positive change in OI combined with a rising price is what defines long buildup; the same positive COI with a falling price defines short buildup; a negative COI with falling price is long unwinding; and a negative COI with rising price is short covering. Without tracking the change rather than just the absolute OI number, none of these four patterns can be identified at all.

On an option chain, COI is usually shown as its own column next to each strike’s OI, updating through the session so traders can watch, strike by strike, where fresh positions are being added or closed in near real time. At the market-wide level, the same metric powers OI gainers and OI losers screeners, which simply rank every F&O contract by the size of its change in OI to surface the most active positioning of the day.

One thing to keep in mind: COI can turn sharply negative purely because of expiry-week rollover, as traders shift positions from the current contract to the next one, which has nothing to do with a change in market view. Because of this, COI is best read together with volume and with what’s happening in the next expiry’s OI, rather than in isolation, especially during the last couple of sessions before a Nifty or Bank Nifty expiry.