Open Interest Explained

Open interest counts how many option contracts are still open, and reading it alongside volume reveals whether new money is entering or old positions are closing.

What open interest measures

Open interest is the total number of options contracts, for a given strike and expiration, that are currently open: bought and not yet closed, exercised, or expired. It's a running headcount of outstanding positions, updated once per day, not a live tally like volume. If open interest on a particular call is 5,000 contracts, that means 5,000 contracts' worth of that exact option currently exist as live positions somewhere in the market.

Every open contract has a buyer on one side and a seller on the other, so open interest doesn't tell you which side is bullish or bearish — only that a position exists and hasn't been unwound.

Open interest vs. trading volume

Volume counts how many contracts changed hands during a single session, a flow measure that resets to zero each day. Open interest counts how many contracts remain outstanding after all that trading, a stock measure that carries forward. A contract can trade heavily in a day while open interest barely moves, if most of that volume is existing holders trading with each other rather than new positions being created.

The distinction matters for interpretation: a volume spike alongside rising open interest suggests new money establishing fresh positions, while a volume spike alongside falling open interest suggests existing positions being closed out.

Reading rising and falling open interest

Rising open interest alongside a rising price is often read as new buyers stepping in and confirming a trend, while rising open interest alongside a falling price can suggest new bearish bets building. Falling open interest, regardless of price direction, generally signals that positions are being closed rather than opened — conviction fading rather than building.

None of these reads are mechanical rules; they're context clues traders combine with price action and volume, not standalone signals. Open interest by itself doesn't reveal whether the underlying positions are hedges, speculative bets, or something else entirely.

Expiration effects on open interest

Open interest is concentrated at specific expiration dates, and as those dates approach, the strikes carrying the largest open interest can become magnets for price action, since market makers hedging those positions need to adjust their stock holdings as expiration nears. After expiration, all open interest in that series disappears at once — contracts are exercised, assigned, or expire worthless, and the count resets for that series.

Traders watching heavy open interest at a round-number strike into a monthly or weekly expiration are often trying to anticipate exactly this kind of hedging-driven pinning behavior, which also underlies theories like max pain, discussed in its own guide.