What it means
Every futures or options contract has a buyer on one side and a seller on the other, and open interest counts each of those matched pairs once. When a new buyer and a new seller create a fresh contract, open interest rises by one; when both sides close out, it falls by one.
Open interest is often confused with trading volume, but the two measure different things. Volume counts how many contracts traded during the session, including traders who opened and closed a position within minutes, while open interest counts only what is still outstanding when the bell rings.
For a business, open interest matters most as a liquidity signal. A commodity contract with large open interest is usually easy to enter and exit at a fair price, which is exactly what a finance team wants when hedging fuel, grain or currency exposure.
Analysts also read open interest alongside price. Rising prices with rising open interest suggest new money is backing the move, while rising prices with falling open interest often mean traders are simply closing out losing short positions.
One nuance catches people out: open interest is reported with a delay, usually the following morning, because exchanges reconcile positions overnight. It also concentrates in particular expiry months, so a headline figure covering all expiries can hide the fact that only one contract month is genuinely liquid.
In practice
Real-world examples.
Example
A bakery chain wants to fix its wheat cost for next year. The treasurer compares two futures expiry months and picks the one with open interest of 180,000 contracts over the one with 4,000, because the busier month means orders will fill close to the quoted price.
Example
An equity analyst notices that open interest in a mining company's call options has tripled in a fortnight while the share price has crept up. She flags it to the desk as a sign that traders are building new bullish positions ahead of a resource announcement, rather than just churning existing ones.
Example
A treasury team at an importer holds currency futures and checks open interest weekly. When it starts falling sharply into the expiry month, the team rolls its hedge forward early rather than risk wide spreads in a thinning market.
Think of it
“Open interest is how many contracts are still open-outstanding positions not yet closed.
Formula
Calculation
Closing open interest = opening open interest + contracts newly opened - contracts closed
A crude oil futures contract starts the day with 12,000 contracts outstanding. During the session traders open 3,000 brand new positions and close out 1,800 existing ones, so closing open interest is 12,000 + 3,000 - 1,800 = 13,200 contracts.
To see what that represents in money terms, multiply by the contract size and the price. Each contract covers 1,000 barrels and oil is trading at $70 a barrel, so the notional value of all open positions is 13,200 x 1,000 x $70 = $924,000,000.Case study
Seen in the real world.
Northbeam Freight is an illustrative haulage company invented to show how open interest is used in practice. Its finance director wanted to hedge twelve months of diesel purchases and asked a broker for the cheapest available contract month.
The broker came back with two options at almost identical prices, but very different open interest: 96,000 contracts in one month and 2,300 in another. Northbeam chose the busier contract, accepting a marginally worse quoted price in exchange for the confidence that it could unwind the hedge quickly if fuel volumes changed.
Six months later the company won a contract that cut its fuel needs by a third. It exited part of the hedge in a single morning with barely any price impact, something the thin contract month would not have allowed. The fictional example makes a simple point: liquidity is a cost you pay for only when you need it.
Watch out
Common mistakes.
- Treating open interest and volume as the same number. Volume is activity during the day, while open interest is the stock of positions still outstanding at the end of it.
- Assuming high open interest means prices will rise. It says how much money is committed, not which direction that money is betting.
- Looking only at total open interest across all expiries. Liquidity is usually concentrated in one or two front months, and the total hides that concentration.
Questions
People also ask.
Does open interest count both the buyer and the seller?
No, one contract with a buyer and a seller counts as one unit of open interest, not two.
Why did open interest fall on a day with heavy trading?
Because most of that trading was existing holders closing positions with each other rather than new positions being created.
Is open interest relevant to ordinary shares?
No, shares have a fixed count in issue, so the concept applies to derivatives such as futures and options where contracts are created and destroyed.
From the founder's library
Take it further with the book.
Build your financial confidence beyond this definition. Shihan's full-length guide, Accounting Fundamentals, takes the same plain-English approach and turns it into a complete, practical playbook for non-finance managers, business owners and students - with chapter-end quiz answers and presentation slides included.
25% off with code MMHQ25, applied at checkout. Priced in USD - checkout may show the equivalent in your local currency.
View the book and save 25%Related