Delta

Delta measures how much an option's price is expected to change for a one-point move in the underlying, ranging from 0 to 1 for calls and -1 to 0 for puts. A 0.50-delta call gains roughly half a point for every one-point rise in the underlying. Delta also serves as a rough hedge ratio and an informal proxy for the probability an option finishes in the money.

Delta sits at the base of the options Greeks. At the money, a call typically has a delta near 0.50, meaning the market is roughly split on whether the contract finishes in or out of the money. Moving deeper in the money, delta climbs toward 1 (put delta toward -1) as the option behaves more like the underlying itself; moving further out of the money, delta shrinks toward 0 as the option's payoff becomes less connected to small price moves.

Delta is not fixed. It moves as the underlying moves - that rate of change is gamma - it drifts as time passes - that drift is charm - and it shifts as implied volatility changes - that cross-effect is vanna. Delta is therefore best read as a snapshot: the directional exposure an option carries right now, not a static number.

Because delta approximates how many shares of the underlying one contract behaves like, it doubles as a hedge ratio: a dealer holding a position with 100 deltas of exposure can offset it with roughly 100 shares (or the equivalent futures/index exposure) of the underlying. Summed across every strike and expiration, that aggregate figure becomes the dealer's overall directional hedge - see dealer delta exposure.

In 0DTE contracts, delta behaves in an unusually binary way. With little time left, an option's delta moves quickly toward 0 or toward 1/-1 as price crosses the strike, since there is barely any remaining time value to blur the outcome. That fast-moving delta is part of why same-day options require such active, continuous hedging into the close.

Calls and puts at the same strike and expiration are linked by a fixed relationship: call delta minus put delta equals 1, a mechanical identity known as put-call parity rather than a market view. A 0.60-delta call therefore always pairs with a -0.40-delta put at that same strike, and buying the call while selling the put replicates a position in the underlying itself.

Because delta captures both how far out of the money a strike sits and how much time remains to expiration in a single number, it doubles as the standard way to compare strikes across different expirations on equal footing. Rather than describing a strike by its raw distance from the current price, traders commonly describe it by its delta - a '10-delta put' or a '25-delta call' - since two strikes with the same delta carry roughly comparable odds of finishing in the money even if they sit at very different price distances or expiration dates. The 25-delta skew, a standard volatility metric, is built directly on this convention.

Delta does not only describe a single contract. Summed across every position in a portfolio, or, at the dealer level, across an entire chain of customer positions, it produces a single net figure describing overall directional exposure. That aggregate, applied to a whole dealer book rather than one contract, is what dealer delta exposure (DEX) measures, turning the same per-contract concept into a structural, chain-wide estimate.