What is open interest in options?
Open interest is the number of option contracts that exist right now: positions that have been opened and not yet closed, exercised or expired. Every contract has a buyer and a seller, and one contract counts once.
Open interest versus volume
Volume counts contracts traded in a session. Open interest counts contracts outstanding at the end of it. A single trade can move them differently:
| Trade | Volume | Open interest |
|---|---|---|
| A buyer opens a new position against a seller who is also opening | +1 | +1 |
| A holder sells to close, to a new buyer opening | +1 | unchanged |
| A holder sells to close, to a seller who is also closing | +1 | −1 |
So a busy day with flat open interest means positions changed hands; a day where open interest jumps means new risk was created.
Why it matters for the stock
Every open contract has a counterparty, and the largest counterparties are market makers who hedge in the underlying. The bigger the open interest, the larger the hedging book behind the stock and the more the stock’s own trading is shaped by that hedging. That is the whole premise of this site: treat the entire open interest of a ticker as one portfolio, compute its greeks, and find the prices where the hedging flips.
Two levels fall out of that portfolio: the delta neutral price, where its summed delta is zero, and gamma max, where its summed gamma peaks.
How this site reports it
Every ticker page shows total open interest across all listed contracts, the change versus the previous session, and, for tickers with a full history page, the one-year percentile and the 5- and 21-session change. The most open interest screen lists the hundred largest chains each day, and open interest surge lists where it grew fastest over five sessions.
Open interest is reported once a day after the close, by the exchanges, which is why all of this site’s numbers are end-of-day.