Open interest is the total number of outstanding derivative contracts, such as futures or options, that have been opened and not yet offset by an opposite trade, exercised, settled or allowed to expire. Each contract has one buyer and one seller, so a single contract adds one to open interest, not two. The figure is published daily by exchanges and is widely followed as a gauge of participation in a market.
Open interest is often confused with trading volume. Volume counts every contract traded during a period, including trades that simply pass an existing position from one party to another; open interest counts only the positions still standing at a point in time. In crypto, it is especially watched in markets for perpetual futures, which never expire and where positions can build up for long periods.
Open interest in plain terms
Think of a cloakroom at a theatre. Volume is the number of times coats change hands at the counter during the evening. Open interest is the number of coats still hanging on the rails at any moment. A busy counter does not necessarily mean the rails are filling up: people may be collecting coats as fast as others hand them in.
When open interest rises, more people have taken positions and left them open, so more money is committed to the market. When it falls, people are closing positions and taking money off the table. The number does not say who is right, only how many bets are still running.
How open interest is counted
Because every open contract has exactly one long and one short side, open interest can be stated simply:
Whether a trade changes open interest depends on whether each party is opening or closing a position:
- Both sides opening. A new buyer and a new seller create a fresh contract, and open interest rises by the size of the trade.
- One opening, one closing. An existing position is passed from one trader to another, and open interest is unchanged.
- Both sides closing. A long holder and a short holder both exit, the contract disappears and open interest falls.
Worked example
On day one, trader A buys 10 contracts from trader B, and both are opening new positions, so open interest is 10. On day two, trader C buys 5 contracts from trader D, both opening, so open interest becomes 10 + 5 = 15. On day three, A sells 4 contracts to a newcomer, E; A is closing and E is opening, so open interest stays at 15 even though 4 contracts traded. On day four, A sells the remaining 6 contracts to B, who is buying back an earlier short position; both are closing, so open interest falls to 15 − 6 = 9. Total volume over the four days was 25 contracts, while open interest ended at 9.
How traders interpret open interest
Analysts commonly read open interest together with price:
| Price | Open interest | Common reading |
|---|---|---|
| Rising | Rising | New money is entering, supporting the uptrend. |
| Rising | Falling | Shorts are closing; the rise may lack new buyers. |
| Falling | Rising | New short positions are building, supporting the downtrend. |
| Falling | Falling | Longs are closing out; selling pressure may be easing. |
Very high open interest combined with heavy use of leverage can signal fragility. If prices move sharply, many leveraged positions may hit their margin limits at once, setting off cascading liquidations. In perpetual markets, traders also compare open interest with the funding rate to judge whether longs or shorts are more crowded. In options markets, open interest at particular strike prices shows where large positions sit, which some traders watch near expiry.
Open interest in crypto markets
Crypto derivatives trade on many venues at once, including regulated exchanges such as the CME and large offshore platforms. Data providers add up open interest across exchanges, usually quoted in dollar terms rather than contract counts. That dollar figure rises when prices rise even if no new contracts are opened, so changes should be read with care. Reporting standards also differ between venues, and some platforms are less transparent than regulated futures exchanges.
Limitations
Open interest shows how many positions are open, not which side holds the stronger hand, and every long is matched by a short. It can be distorted by contract rolls before expiry, by hedging activity unrelated to market views, and by changes in contract size. It is best treated as one input alongside price, volume and broader liquidity conditions, not as a forecast. Related concepts are explained under futures contract and the options market.