Open Interest vs Volume in Options: What Each Number Tells You
Volume counts the contracts traded in a session; open interest counts contracts still open. How to read a volume spike and what the next day's reading adds.
Volume is the number of option contracts traded during one session; open interest is the number of contracts still open after it. Most explanations of open interest vs volume stop there. What matters when a contract suddenly trades thousands of times is what each number can and cannot tell you: a volume print says trading happened, the next day's open interest says whether positions were added, and neither says who holds them or why.
What is open interest in options?
Open interest counts the contracts in an option series that have been opened and not yet closed, exercised or expired. The Options Clearing Corporation calculates it by consolidating the exchanges' trade reports of each day's opening and closing transactions, and publishes a daily open interest report.
Every options order is marked to open or to close: buy to open, buy to close, sell to open, sell to close. When both sides of a trade open a position, open interest rises by that many contracts. When both sides close, it falls. When one side opens and the other closes, the contract changes hands and open interest is unchanged. An exercised option that results in assignment is treated as closed and removed, and contracts that expire leave open interest with them. The Options Industry Council sets out these mechanics in its October 2025 note, Open Interest: Why It Matters.
Open interest vs volume: what each number counts
Volume counts activity within a session and resets to zero at the next open. Open interest counts positions, and it carries from one session to the next.
The two can diverge widely. The same contract can trade many times in one day, and each trade adds to volume while open interest moves by at most one contract per contract traded. A contract's volume can therefore run far past its open interest without a single new position surviving the close.
Why does a volume spike not prove positions were added?
A contract that normally trades a few hundred lots and suddenly trades 4,000 looks like someone built a position. The volume number alone cannot confirm that. The same 4,000 contracts are consistent with new positions on both sides, with existing holders exiting, or with a handful of contracts passing between traders through the day. Each case prints the same volume.
Open interest is a settled figure: the OCC consolidates the day's transactions after the session, so the trades behind a volume spike appear in the next reading. Until it lands, all the spike confirms is that trading happened.
How do you read the next day's open interest?
The table below is an illustration with round numbers, not a real contract. The session starts with 500 contracts open and trades 4,000. Open interest can change by at most the session's volume, and it cannot fall below zero.
| Next-day open interest | Change | What it is consistent with |
|---|---|---|
| 4,400 | +3,900 | Nearly every trade opened positions on both sides. Positions were added. |
| 2,000 | +1,500 | Some positions were added. Most of the volume was contracts changing hands, or opens offset by closes. |
| 300 | -200 | Net closing. More contracts were closed than opened, and the rest of the volume changed hands. |
Even the first row leaves two things unknown: which side initiated the trades, and why. A large block of puts can be protection on shares the buyer already owns. Rising open interest in calls can be holders of the stock writing covered calls against it. The number confirms that contracts are open; it carries no direction.
What open interest and volume do not show
Neither number identifies the buyer or the seller, or the reason for the trade. Neither says whether a position is a bet, a hedge or one leg of a spread. Reading a put spike as bearish or a call spike as bullish adds a claim the data does not carry.
How our options board uses this
Our options board applies this reading each session: it compares every contract's volume with the prior session's open interest and flags the contracts where volume is above 1,000 and above three times that open interest. The following session it posts the new open interest beside each flagged row, so the spike and its settlement sit together. The data is end-of-day. For the 15-minute delayed view of the same contracts during the session, and the largest prints published after the close, see unusual options activity during the session.
See the options board and its next-session open interest follow-up →
Frequently asked questions
What is open interest in options?
Open interest is the number of contracts in an option series that remain open, meaning they have not been closed, exercised or expired. The OCC calculates it from the opening and closing transactions the exchanges report each day.
Can volume be higher than open interest?
Yes. Volume counts every contract traded in a session, and the same contract can change hands many times in a day, so a contract's volume can exceed its open interest. Open interest itself can change by at most the session's volume.
Does high open interest mean bullish or bearish?
Neither. Open interest counts open contracts without saying who holds them or why. A large put position can be a hedge on shares the holder already owns, so neither open interest nor volume shows direction on its own.
What does high open interest with low volume mean?
Many contracts remain open while few traded that session. Existing positions are being held rather than opened or closed. It does not show who holds them or why.
When does open interest update?
Open interest is a settled figure. The OCC consolidates the day's opening and closing transactions after the session, so trades from one session appear in the next open interest reading rather than during the day.
Educational content, not investment advice.