Options trading
Open interest (OI)
Definition
The number of option contracts in a series that are still open at the end of a trading day: opened earlier and not yet closed, exercised, assigned or expired.
Example
Say a $50 call series has open interest of 1,000 contracts at Monday’s close. On Tuesday, 300 contracts trade between a buyer and a seller who are both opening, and 100 more between two traders who are both closing, so the day’s volume is 400 while open interest ends at 1,200. Volume counts every trade; open interest counts only what is still open.
Hypothetical numbers, for illustration only.
Also defined in
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