Open Interest

Formula

Open Interest counts each open contract once (one long matched with one short), so it is not the sum of buy and sell sides. Change in OI for a period = OI at end of period − OI at start of period.

How it is read

OI is commonly read alongside price movement to describe how positions are forming or unwinding. The four standard price-plus-OI combinations are: rising price with rising OI is termed a "long buildup" (fresh long positions being added); falling price with rising OI is termed a "short buildup" (fresh short positions being added); rising price with falling OI is termed "short covering" (existing shorts closing out); and falling price with falling OI is termed "long unwinding" (existing longs closing out). Traders also look at where OI is concentrated across strikes to gauge which levels carry large outstanding positions. Volume measures contracts traded in a period, while OI measures contracts still open, so the two are read together rather than interchangeably.

What it does not tell you

OI tells you how many contracts are open, not who is right or which direction price will move next; the buildup labels describe what positions did, not what happens afterward. Because every open contract has a long and a matching short, OI alone does not reveal which side is "stronger" or who initiated the trade. OI can shift sharply around expiry as contracts are settled or rolled to the next series, and a single instrument's OI can be misread without the context of price, volume, and the wider option chain. Data is published with the exchange's reporting cadence, so intraday figures may differ from end-of-day settled numbers.