What is open interest?

Open interest is the total number of derivative contracts — such as futures or perpetual swaps — that are currently open and not yet settled or closed. Unlike trading volume, which counts how many contracts changed hands over a period, open interest is a running total of live positions at a given moment. It is one of the core structural metrics for any crypto derivatives market.

This article explains what open interest measures, how it rises and falls, and how it differs from volume. It is educational only and describes market structure; it is not a signal and offers no guidance on positioning.

What open interest measures

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

Because it counts positions that are still live, open interest tells you how much exposure is currently held in a market. A rising figure means more contracts are open than before; a falling figure means positions are being closed faster than new ones are opened. It is a snapshot of commitment outstanding, taken at a point in time.

How open interest goes up and down

Whether a trade changes open interest depends on whether it opens new positions or closes existing ones. There are four cases when a buyer and a seller are matched:

The key insight is in the bottom two rows: a trade can occur — adding to volume — without changing open interest at all, because one trader is simply handing an existing position to another. Open interest only moves when new contracts are created or existing ones are extinguished.

Open interest vs trading volume

These two are often confused 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 (for example, daily volume). A contract opened and closed within the same day adds to volume twice but leaves open interest unchanged.
• Open interest is a level: it is the stock of contracts still open right now, carried forward until those positions are closed. It does not reset with each period.

A useful analogy: 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 these relationships is structural observation, not a trading signal.

Why open interest matters for market structure

Open interest is a measure of how much leverage and exposure is committed to a derivatives market. Several structural points follow from it:

• It sizes the market’s outstanding exposure. A larger open interest means more capital is tied up in live positions that must eventually be closed or settled.
• It provides 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 of that are covered in how liquidations cascade.
• It complements funding and price data. On perpetual markets, open interest is usually read alongside funding rates to understand how crowded and how leveraged each side is. See how perpetual futures work for the contract mechanics.

These are descriptions of what the number reflects, not 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 opens 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 is closing a long; C is closing a long. One contract is extinguished, so open interest falls to 1 — even though this trade added to the day’s volume.

By the end, three trades have occurred (three units of volume), but open interest sits at 1. The example shows the core mechanic: volume records activity, while open interest records how many positions remain 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 are 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.

A subtlety worth noting: because the same underlying asset trades on many venues, aggregated open interest depends on which venues are 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 type of contract. A dated futures contract has an expiry, and as that date approaches, open interest typically 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 relatively short window.

A perpetual contract has no expiry, so there is no forced unwind date; open interest simply reflects however many positions are currently held, held in line by the funding mechanism rather than by an approaching settlement. This difference is why open interest is read slightly differently on dated versus perpetual markets: on the former it interacts with the expiry calendar, while on the latter it is 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 does not 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 does not tell you whether longs or shorts dominate; it is the total of open contracts, both sides included. It is 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 are closed, and is unchanged 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 market structure, but the metric itself is descriptive and carries no built-in signal.