Open interest (OI) is a number derivatives traders watch closely — and one that's widely misread. Here's what it actually tells you.
What open interest is
Open interest is the total number of derivative contracts (futures or options) that are currently open — not yet closed or expired. Unlike volume, which counts trades in a period, OI counts outstanding positions at a point in time.
- A new buyer and new seller opening a position → OI rises.
- Both sides closing → OI falls.
- One closing, one opening → OI unchanged.
Why traders watch it
OI hints at how much "fuel" is committed to a move:
- Rising price + rising OI — new money backing the up-move (often seen as strength).
- Rising price + falling OI — a move driven by closing shorts, which can run out of steam.
- OI build-up at a strike — large option OI at a level can act as a magnet or a battleground near expiry.
The big caveat
OI is widely misused. It is not a directional signal on its own — every open contract has a buyer and a seller, so OI alone never tells you which side is "right." Treat it as context about participation, not a crystal ball.
Using it sensibly
Combine OI with price action, the index trend and support/resistance. And whatever the OI picture, the trade is still governed by your stop and position size.
Open interest tells you how many are committed — not who's correct. Read it as context, never as a verdict.
Education only — not financial advice.