Direct Answer
Option open interest is the number of option contracts that have been opened and not yet closed, exercised, or expired. It is reported once per day, typically by the clearing house, for each contract. Rising open interest alongside volume means new positions are being added; falling open interest means positions are being closed.
Option Open Interest: Formula, Meaning, Signals, Examples and How to Use It
How Is Option Open Interest Calculated?
Option open interest is the number of option contracts that have been opened and not yet closed, exercised, or expired. It is reported once per day, typically by the clearing house, for each contract.
Formula: OI_today = OI_yesterday + contracts opened - contracts closed, exercised or expired
Inputs:
- Previous day's open interest for the contract
- Contracts newly opened that day
- Contracts closed, exercised or expired that day
Worked example. A contract with 12,000 open contracts, 3,500 new openings and 1,800 closings ends the day at 13,700. The inputs are illustrative numbers, not market data.
Reading it. Rising open interest alongside volume means new positions are being added; falling open interest means positions are being closed. It indicates the size of the outstanding contract base, not the direction of participants.
Limits. It updates once a day, so intraday values are the prior close. Each contract has a buyer and a seller, so open interest does not show which side is bullish. Vendors can differ slightly in revision timing.
What is Option Open Interest?
Option open interest is the number of option contracts that have been opened and not yet closed, exercised, or expired. It is reported once per day, typically by the clearing house, for each contract.
How to use Option Open Interest
Rising open interest alongside volume means new positions are being added; falling open interest means positions are being closed. It indicates the size of the outstanding contract base, not the direction of participants. A reading alone is never a buy or sell signal; it needs context from price structure, volume, volatility and the broader market regime.
Strengths
- It is a stock rather than a flow: it accumulates openings and subtracts closings, so it shows how many contracts remain outstanding.
- Being published by the clearing organization after each session, it is an official count and not an estimate built from trades.
- Reproducible when the formula and data convention are fixed.
Weaknesses and limitations
- A day with equal opening and closing activity leaves open interest unchanged, so heavy trading can occur with no visible change.
- Contracts disappear at expiry, so open interest series show a built-in drop on expiration dates that is not a market view.
- Correlated indicators can create false confidence by repeating the same underlying information.
Editorial and risk note
This page is educational content, not individualized investment advice. It should not imply guaranteed prediction, accuracy or outperformance.
Frequently Asked Questions
Is Option Open Interest a buy or sell signal?
No. Rising open interest alongside volume means new positions are being added; falling open interest means positions are being closed. It updates once a day, so intraday values are the prior close. A trade built on it still needs a trigger, an invalidation rule, a position size and realistic execution assumptions.
What is the best setting for Option Open Interest?
Option Open Interest takes these inputs: previous day's open interest for the contract; contracts newly opened that day; contracts closed, exercised or expired that day. There is no universal best setting for the tunable ones, so test them across instruments, regimes and out-of-sample periods and favor stable parameter regions over one historical winner.
Can Option Open Interest be used by itself?
It updates once a day, so intraday values are the prior close. Each contract has a buyer and a seller, so open interest does not show which side is bullish. Vendors can differ slightly in revision timing. For that reason it is read next to measures of direction, participation, valuation, liquidity and risk, not alone.
Does Option Open Interest work on every timeframe?
The calculation (OI_today = OI_yesterday + contracts opened - contracts closed, exercised or expired) can be run on any bar size, but behavior is not portable: a reading on a five-minute chart describes a very different market window from the same reading on a daily chart. Validate the exact timeframe before relying on it.
Why does Option Open Interest give false signals?
A day with equal opening and closing activity leaves open interest unchanged, so heavy trading can occur with no visible change. Contracts disappear at expiry, so open interest series show a built-in drop on expiration dates that is not a market view. Lag, noise and regime changes add to this, because market participants react to new information after the reading is calculated.
How should Option Open Interest be backtested?
Rebuild Option Open Interest from previous day's open interest for the contract using point-in-time data, write the rules before testing, include delisted securities where relevant, model realistic fills and costs, reserve a validation sample and compare with a simpler baseline.