Courses
Open Interest vs. Volume: What They Tell You
Volume measures a single day's trading activity, while open interest tracks total open contracts over time — together they signal how easily a position can be exited.
Volume counts today's trades. Open interest counts contracts still open. They tell you very different things.
Two counters, two questions
Volume is how many contracts of a specific option traded during today's session — it resets every day. Open interest is how many contracts are currently open — bought or sold and not yet closed, exercised, or expired — and it carries forward until a position is actually closed.
Volume tells you how active a contract was today. Open interest tells you the total commitment built up in that contract over its whole life so far. A quiet day can still sit on top of high open interest built over weeks; a single huge-volume day doesn't necessarily add to open interest if most of it was same-day trading in and out.
Worked example
Tracking one contract — the XYZ $50 call expiring in 30 days — across three days:
| Day | Volume (today's trades) | Open interest (contracts still open) |
|---|---|---|
| Monday | 200 contracts traded | 1,000 contracts open |
| Tuesday | 150 contracts traded, but 150 of those closed existing positions | 850 contracts open |
| Wednesday | 400 contracts traded, mostly new positions opened | 1,200 contracts open |
Tuesday had real activity, but because most of it closed existing positions, open interest actually fell. Wednesday's volume was high and open interest jumped — that day's trading was mostly new positions opening, not old ones closing.
Why it matters for liquidity
High open interest generally means more participants are willing to trade that specific strike and expiration, which tends to produce tighter bid-ask spreads (the next lesson's topic). Very low open interest — even a handful of contracts — can mean a position is hard to exit cleanly later, no matter how volume looked on the day you got in.
Key takeaway: Volume shows today's activity; open interest shows total commitment — check both before trusting that a contract will be easy to exit later.
That "easy to exit" question comes down to one more number: the bid-ask spread, covered next.
This lesson is educational content explaining standard options mechanics, not personalized investment or trading advice.
« Back to Options Basics