What is delta in options?

What delta measures

Delta is the derivative of the option price with respect to the underlying. In practice: a call with a delta of 0.40 gains about 40 cents per share for a one-dollar move, so roughly 40 dollars on a 100-share contract. Calls run between 0 and 1, puts between minus 1 and 0. A multi-leg position’s delta is the sum of its legs.

The figure holds for small moves and for the moment it was measured. Once the underlying has moved meaningfully, delta is a different number — the 40 cents in the example is a snapshot, not a rule that survives the next ten dollars of price movement.

What the values mean in practice

Delta doubles as a share-equivalence measure: 100 delta is roughly 100 shares. That lets you compare the directional load of an entire account regardless of how many legs it is spread across. Deep in-the-money options approach a delta of 1 or minus 1 and behave almost like the stock; far out-of-the-money options approach zero.

Net delta on a multi-leg position therefore says more than the delta of any single leg. A short iron condor sits near zero even though each of its four legs carries a meaningful delta — the directional load largely cancels, and the real risk lives somewhere else.

The common misreading

Delta is often read as the probability of finishing in the money. The two numbers sit close together but are not the same: the approximation comes out of the model and drifts noticeably with pronounced skew and long expirations. The second error is treating delta as fixed — how it changes is exactly what gamma describes.

Strategies where the term matters

• Covered Call — Are you willing to hand over the shares at the call strike - even if they keep running afterwards?
• Protective Put — What does this insurance cost you per year, as a percentage of the position?
• The Wheel — Would you buy and hold this stock even without the option premium?

Related terms

• Gamma
• Theta
• Vega

Every term in one place: the options glossary.