What Is Open Interest in Options Trading?
Open interest in options trading is the total number of outstanding contracts for a specific strike price and expiry date that remain open — not yet closed, exercised, or expired. It represents every active options position across all traders on that particular contract at a given point in time, and Pluang updates the figure once per trading day. Open interest is not the same as trading volume: volume counts how many contracts change hands during a single day, while open interest counts how many contracts are still active once that day's trading ends. Open interest increases when a new buyer and a new seller both open fresh positions in the same contract, and decreases when an existing position is closed, exercised, or expires. As a general rule, higher open interest signals more market participation and deeper liquidity for that specific strike and expiry, making it easier to enter or exit a position near the quoted price — while low open interest often means wider bid-ask spreads and slower order fills.
What moves open interest:
- Increases — a new buyer and a new seller both open positions in the same contract for the first time, so a fresh long and a fresh short are created together.
- Decreases — an existing long position is closed against an existing short position, or the contract is exercised, assigned, or expires.
- Stays the same — an existing holder sells their position to a new trader who is opening a position; one side opens while the other closes, so net open interest doesn't move.
Where to check it on Pluang: Open interest is shown alongside strike price, premium, and trading volume on the options chain for each expiry date, so it can be compared strike by strike before placing an order.
Related questions:
Q: What's the difference between open interest and trading volume?
Trading volume counts every contract bought or sold during a single day, even if the same contract changes hands multiple times, while open interest counts only the contracts still open once that day ends. A contract can show high volume with little change in open interest if most trades are simply closing out existing positions. Both figures are useful together: volume shows how actively a contract is trading now, while open interest shows how many positions are currently outstanding.
Q: Does high open interest mean an option is a good investment?
No — open interest is a liquidity indicator, not a signal of profitability or price direction. A contract with high open interest simply means more positions are outstanding, producing tighter bid-ask spreads and easier order execution. It says nothing about whether the underlying stock will move in a trader's favor, and options with high open interest can still expire worthless. Read it alongside strike price, premium, and expiry — not as a standalone buy or sell signal.
Q: Where can I check the open interest for a specific options contract on Pluang?
Open interest is displayed on the options chain screen for each underlying stock or ETF, listed next to strike price, premium, and trading volume for every available expiry date. Because open interest is tied to one specific strike-and-expiry combination, the same underlying asset can show very different open interest figures across its various contracts. Checking this figure before placing an order helps gauge how liquid a particular strike and expiry are likely to be.
Q: Why does open interest change from one day to the next?
Open interest changes because it reflects the net result of positions opened and closed since the previous count. If more new positions are opened than are closed, exercised, or expired on a given day, open interest rises; if more positions are closed than opened, it falls. Near an expiry date, open interest for that expiry typically declines as traders close out positions or let contracts expire, which is a normal pattern rather than a warning sign on its own.