Open Interest

Open interest is a count of how many contracts of a specific options or futures listing are currently active — meaning opened but not yet closed, expired, or exercised. It answers a simple question: how many contracts of this exact strike, expiration, and type actually exist right now that someone is holding open?

Every contract has two sides, a buyer and a seller. When a brand-new contract is created — a buyer and seller trade with each other and both are opening new positions — open interest goes up by one. When two existing holders close out their positions against each other, open interest goes down by one. But if one trader opens a new position and the other side is simply closing an old one, open interest stays flat, because a contract that already existed just changed hands. This is the part people trip on: trading volume tells you how much activity happened in a day, but open interest tells you how many of those trades actually created new exposure versus just passing an existing contract along.

Open interest is reported with a one-day lag on most platforms — the number you see is typically calculated from the previous session's activity, not live. That lag matters if you are trying to read open interest intraday, since it will not yet reflect today's trades.

A high open interest number generally signals a strike or contract that many participants care about, which tends to mean tighter bid-ask spreads and easier order fills. A low number can mean the opposite: thin interest, wider spreads, and the risk that a decent-sized order moves the price more than expected.