Skip to content
Theta Vantage
Connect your AISign in

25% off your first 3 months of Pro, or your first year on yearly, with FALL25, through Nov 6.

For a first Pro subscription. The 7-day free trial comes first.

See pricing

Open interest

Also called OI

The number of option contracts open at a strike and expiration, published once a day as of the previous close.

Open interest (OI) is how many contracts of an option are open: opened and not yet closed, exercised, or expired. A trade can raise it (both sides opening), lower it (both closing), or leave it unchanged (one side handing the position to another).

Open interest is counted after the close and published once a day, before the next open. Every number in Theta Vantage that uses it describes positions as of the previous close.

Why it matters here

  • Every dealer exposure and level (GEX, the walls, zero gamma, max pain) is weighted by open interest.
  • Contracts opened today carry no open interest until tomorrow. On a busy 0DTE session the day's real positioning can differ a lot from the estimate.
  • Through the session, open interest stays fixed, so the intraday heatmap shows yesterday's positions re-weighting as price, time, and volatility move.

Volume is different

Volume counts contracts traded in the session, whatever they did to open interest. The option chain shows both. A flow larger than the open interest is marked unusual, since it can't all be closing trades.

Where it appears

Related terms

All 52 terms