What Is Open Interest? | How Do Futures Work?

Open interest is the total number of futures contracts in a market that are still outstanding, meaning they have been opened and not yet closed, delivered, or expired. Each open contract has one long and one short, so open interest counts contracts, not sides.

Open interest vs volume

Volume counts how many contracts traded during a session. Every trade adds to volume.
Open interest counts how many contracts are still open at the end of the day. Only some trades change it.

A market can have huge volume and flat open interest if traders are mostly passing existing positions back and forth.

How it changes

Buyer	Seller	Effect on open interest
Opens a new long	Opens a new short	+1 (a new contract is created)
Opens a new long	Closes an existing long	0 (the position changed hands)
Closes an existing short	Opens a new short	0 (the position changed hands)
Closes an existing short	Closes an existing long	-1 (a contract is extinguished)

A tiny example

Monday, open interest in a contract is zero.

Ana buys 10 contracts from Ben, both opening positions. Open interest: 10.
Chris buys 4 contracts from Ana, who is closing part of her long. Open interest: still 10 (Ana 6 long, Chris 4 long, Ben 10 short).
Ben buys back 6 contracts from Ana, both closing. Open interest: 4.

Volume for the day was 10 + 4 + 6 = 20 contracts. Open interest ended at 4.

Where to find it

Exchanges publish volume and open interest for every contract, usually the next morning for the prior day. The CFTC’s weekly Commitments of Traders report breaks open interest down by trader category.

What it can tell you

Liquidity. Contracts with high open interest usually have tighter bid-ask spreads and more resting orders.
Which month is active. Open interest moves from the front month to the next contract around the roll, as positions are closed in one and opened in the other. See rolling futures contracts.
Participation. Rising open interest means new money is entering positions; falling open interest means positions are being closed.

What it cannot tell you

Open interest says nothing about whether the new positions are bullish or bearish, since every long has a matching short. Popular rules of thumb that combine price direction and open interest are not reliable signals, and this site does not offer trade ideas. Treat open interest as a measure of size and liquidity, not of direction.

A quick check before trading a contract

Compare open interest across months. A deferred month with very little open interest can be costly to get in and out of, even if the front month is very liquid. This matters most for smaller contracts and for trades held near expiry.