What Is Open Interest?
Open interest is the total number of outstanding option contracts that have not been settled or closed. High open interest indicates liquidity and institutional activity.
Definition
Open interest (OI) is the total number of open options contracts that exist at a given strike and expiration — contracts that haven't been exercised, expired, or closed. When a new buyer and seller create a contract, OI increases by 1. When a contract is closed, OI decreases by 1.
Volume counts how many contracts traded today; open interest counts how many exist in total. Volume resets to zero each day; OI carries over. A spike in volume that increases OI means new positions are being opened. Volume without OI change means traders are closing existing positions.
High open interest at a specific strike (a 'max pain' strike) often acts as a gravity point near expiration, as market makers who sold those options have incentive to keep the stock near that level to minimize their losses.
Real-World Example
TSLA has a $250 call with 50,000 open interest. This means 50,000 contracts (representing 5 million shares) are held by traders betting TSLA stays below $250 (sellers) and traders hoping it rises above (buyers). High OI at this strike means the level is being watched by a lot of money.
Why It Matters
Open interest helps identify which strikes matter — high OI levels often act as support or resistance, and high OI overall means you can enter and exit positions without moving the market against yourself.
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Frequently Asked Questions
What is the difference between options volume and open interest?
Volume counts contracts traded today (resets daily). Open interest counts all outstanding contracts (builds over time). High volume with rising OI = new positions opening. High volume with falling OI = existing positions closing. Both together give a more complete picture of market activity.
What is max pain in options?
Max pain is the strike price where the most option contracts (both calls and puts) would expire worthless, causing maximum financial loss for option buyers. The theory is that stocks tend to drift toward max pain near expiration as market makers hedge. It's a controversial but watched indicator.
Is high open interest always good?
High open interest means liquidity — tight bid/ask spreads and easy entry/exit. For traders, this is almost always a positive. Very low open interest can trap you in positions where you can't exit at a fair price.
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