What is open interest?

Two numbers dominate any crypto derivatives screen: volume and open interest. Open interest is the total number of derivative contracts — futures or perpetual swaps, say — that are currently open and not yet settled or closed. Volume counts how many contracts changed hands over a period; open interest is a running total of live positions at a single moment. It’s one of the core structural metrics for any derivatives market.

What follows explains what open interest measures, how it climbs and falls, and how it differs from volume. It’s educational and describes market structure. It’s not a signal, and it offers no guidance on positioning.

What open interest measures

Every derivative contract has two sides: one party is long, the other short. A single open contract counts as one unit of open interest — the long and the short together are one outstanding agreement, not two. Open interest is the sum of all such outstanding contracts that haven’t been closed out or settled.

Because it counts positions that are still live, open interest tells you how much exposure a market is currently carrying. A rising figure means more contracts are open than before. A falling one means positions are closing faster than new ones open. Think of it as a snapshot of commitment outstanding, taken at a point in time.

How open interest goes up and down

Whether a trade changes open interest hinges on one thing: does it open new positions or close existing ones? When a buyer and a seller are matched, there are four cases:

The lesson lives in the bottom two rows. A trade can happen — adding to volume — without shifting open interest at all, because one trader is simply passing an existing position to another. Open interest only moves when contracts are genuinely created or extinguished.

Open interest vs trading volume

These two get confused constantly, because both are measured in contracts. But they describe different things:

• Volume is a flow. It counts every contract traded during a period and resets each period — daily volume, for instance. A contract opened and closed within the same day adds to volume twice yet leaves open interest untouched.
• Open interest is a level. It’s the stock of contracts still open right now, carried forward until those positions close. It doesn’t reset each period.

Here’s an analogy that sticks: volume is how many times a seat changed hands today; open interest is how many seats are currently occupied. High volume with flat open interest suggests positions are turning over between traders. Rising open interest suggests genuinely new positions are being added. Describing those relationships is structural observation — not a trading signal.

Why open interest matters for market structure

Open interest measures how much leverage and exposure is committed to a derivatives market. A few structural points follow:

• It sizes the market’s outstanding exposure. A larger open interest means more capital tied up in live positions that must eventually close or settle.
• It gives context for liquidations. Because derivatives are often leveraged, large open interest means more positions that could be force-closed if prices move against them. The mechanics are covered in how liquidations cascade.
• It complements funding and price data. On perpetual markets, open interest is usually read next to funding rates to gauge how crowded and how leveraged each side is. See how perpetual futures work for the contract mechanics.

These describe what the number reflects. They aren’t instructions on how to act on it.

A worked illustration

These numbers are invented to show how open interest accumulates, not real market data. Suppose a brand-new futures contract has just launched, so open interest starts at zero:

• Trade 1. Trader A opens a new long and Trader B opens a new short, for one contract. Both positions are new, so open interest rises to 1.
• Trade 2. Trader C opens a new long and Trader D a new short, one contract. Open interest rises to 2.
• Trade 3. Trader A sells their contract to Trader C, who uses it to close their earlier position. A closes a long; C closes a long. One contract is extinguished, so open interest falls to 1 — even though the trade added to the day’s volume.

By the end, three trades have happened (three units of volume), but open interest sits at 1. That’s the core mechanic in miniature: volume records activity, open interest records how many positions stay live once the dust settles.

Where the figure comes from

Open interest is reported by the exchange or clearing venue where the contracts trade, because only the venue knows exactly how many positions sit open on its books. On regulated futures markets, exchanges such as CME publish official open interest for each contract. In crypto, each derivatives exchange reports open interest for its own perpetuals and futures, and aggregators may sum these across venues to estimate a market-wide figure.

One subtlety: because the same underlying asset trades on many venues, aggregated open interest depends on which venues get included, so figures from different data sources may not match exactly. When precision matters, the exchange’s own reported number is the authoritative one for its contracts.

Open interest near expiry and on perpetuals

How open interest behaves over a contract’s life depends on the contract type. A dated futures contract has an expiry, and as that date nears, open interest usually declines: holders close their positions or roll them into a later-dated contract, so the number of open contracts in the expiring one falls toward zero by settlement. A large open interest heading into expiry therefore represents positions that must be closed, rolled, or settled in a fairly short window.

A perpetual contract has no expiry, so there’s no forced unwind date. Open interest just reflects however many positions are currently held, kept in line by the funding mechanism rather than an approaching settlement. And that’s why open interest reads slightly differently on dated versus perpetual markets: on the former it interacts with the expiry calendar, while on the latter it’s a continuous measure of standing exposure. The contract mechanics are covered in how perpetual futures work.

Common misunderstandings

• Confusing it with volume. The most frequent error. A busy day of trading won’t necessarily raise open interest, and open interest can rise on modest volume if those trades open new positions.
• Double-counting the two sides. Each open contract is counted once, not once per side. The long and short together are a single unit of open interest.
• Treating it as directional. Open interest doesn’t tell you whether longs or shorts dominate; it’s the total of open contracts, both sides included. A size measure, not a direction measure.

The bottom line

Open interest is the count of derivative contracts currently open and unsettled — a level, not a flow. It rises when new positions are created, falls when they’re closed, and stays put when an existing position merely passes between traders. Read alongside volume, funding and price, it describes how much exposure and leverage a derivatives market is carrying. Understanding it is fundamental to reading crypto derivatives structure — but the metric itself is descriptive, and it carries no built-in signal.