Volume and open interest are the two activity numbers every futures data page shows, and they are often mixed up. Volume tells you how much was traded. Open interest tells you how much is still open. They answer different questions, they are published on different schedules and they behave differently around a contract's expiry. This guide explains both, shows how a single trade changes them and where they help – and where they do not.
Volume: contracts traded
Volume is the number of contracts that changed hands in a period, usually one trading day. A trade needs a buyer and a seller, but it counts once: if one buyer and one seller trade 10 contracts, volume rises by 10, not by 20. Volume is available live during the session and resets with every new trading day.
It measures activity and, indirectly, liquidity. A contract with high volume usually has narrow bid-ask spreads and absorbs larger orders with less price impact. A contract with low volume can have wide spreads and gaps, which makes a stop order less reliable.
Open interest: contracts still open
Open interest is the total number of contracts that have been opened and not yet closed, delivered or expired. Every open contract has exactly one long side and one short side, and it is counted once. Open interest is a stock, like the number of seats taken in a room; volume is a flow, like the number of people who walked through the door today.
Open interest changes only when positions are opened or closed, not when a contract changes hands between two traders who both stay in it. Here is how a single trade of one contract moves the two numbers:
| Buyer | Seller | Volume | Open interest |
|---|---|---|---|
| Opens a new long | Opens a new short | +1 | +1 |
| Closes an existing short | Closes an existing long | +1 | −1 |
| Opens a new long | Closes an existing long | +1 | 0 |
| Closes an existing short | Opens a new short | +1 | 0 |
The same volume can therefore go together with rising, falling or unchanged open interest. This is why you need both numbers.
When the numbers are published
Volume is available live from the exchange feed during the session; the official daily total, including block trades and other off-exchange trades, is final the next morning. Open interest is different: the exchange calculates it from clearing records after the trading day. CME publishes a preliminary figure that evening and the final figure the next business morning, and many data pages show the previous day's open interest next to today's volume. You cannot see open interest change during the session. Always check the date next to the figure before you use it.
How traders read the combination
A common reading looks at price and open interest together. It is a rule of thumb, not a law, and it works best for trending markets with enough history:
| Price | Open interest | Common reading |
|---|---|---|
| Rising | Rising | New money entering on the long side; the move has fresh participation. |
| Rising | Falling | Mostly short covering rather than new buying; the move may run out of fuel. |
| Falling | Rising | New short positions or trapped longs; the decline has fresh participation. |
| Falling | Falling | Long liquidation; selling pressure may fade once the weak holders are out. |
Treat the table as a question to ask, not an answer. Open interest does not say whether the new positions are hedges or speculation, and a rise can come from one large participant. For the question of who holds the positions, see the COT report guide, which breaks open interest down by trader group once a week. In the COT report, open interest equals the sum of all long positions – including spread positions and the small traders below the reporting level – and, equally, the sum of all short positions.
Open interest, volume and the roll
Each contract month has its own volume and open interest, and many platforms also show the total across all months. The numbers move as contracts approach expiry:
- In the weeks before expiry, volume and open interest drift from the expiring month to the next one. The date on which the next month overtakes the front month is, roughly, the roll (the roll dates on this site follow fixed rules); see roll dates.
- The open interest of an expiring contract falls toward zero at the end, because positions are closed, settled or delivered; see what happens at expiration.
- A drop in the open interest of the front month is therefore not a sign of weakness in the market. Compare the total across months, or the sum of the front two, to see whether participation really fell.
Traders often use the month with the highest volume or open interest as the working contract, because that is where spreads are tightest. Make sure you know the month you trade; see futures symbols and month codes.
Practical rules
- Use volume to judge whether you can trade a contract comfortably today, and open interest to judge how much money is committed.
- Check the date of an open interest figure; it lags by a day.
- Compare open interest across the roll with care: a drop in one month often has a matching rise in the next.
- Do not read a single day's change in open interest as a signal. Look at the direction over several days and together with price.
This guide is general information on market statistics and is not a trading recommendation. Futures trading carries a high risk of loss.
Educational content only – not investment advice. Futures trading involves substantial risk of loss.