Delta
Delta measures how much an option's price is expected to change when the price of the underlying asset moves by one unit. A delta of 0.5 means the option gains about 50 cents for each 1 dollar rise in the underlying.
Typical values
Call deltas range from 0 to 1, and put deltas from 0 to minus 1, because puts gain when the price falls. An at-the-money option has a delta near 0.5 for a call or minus 0.5 for a put. Deep in-the-money options approach 1 or minus 1 and move almost one-for-one with the asset. Far out-of-the-money options have deltas close to zero and barely react to small moves.
Delta changes all the time: when the price moves, when volatility changes and as expiry approaches. The rate at which delta changes is measured by another Greek, gamma.
An example
Say ETH trades at 3,000 dollars and a call option on 1 ETH has a delta of 0.40. If ETH rises to 3,050, the option's price is expected to rise by about 0.40 times 50, or 20 dollars. If ETH falls 50 dollars, the option loses roughly 20. Over larger moves the estimate drifts because delta itself changes.
Delta as exposure and hedge ratio
Delta also tells you how much of the underlying an option position behaves like. Ten calls on 1 BTC each with a delta of 0.3 behave roughly like holding 3 BTC for small moves. Traders who want to be delta neutral, insensitive to small price moves, offset that exposure with an opposite position in the underlying or futures, and adjust it as delta changes. Market makers do this constantly.
Delta is sometimes loosely read as the probability that an option finishes in the money. That is a rough approximation only, not a precise probability.
Limits
Delta is a snapshot for small moves. In fast crypto markets, prices often move far enough that delta-based estimates are clearly off. A delta-neutral position still carries other risks, including volatility changes, time decay and gaps that move faster than any hedge can be adjusted.
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Frequently asked questions
Why do puts have a negative delta?
Because a put gains value when the underlying price falls, its price moves in the opposite direction to the asset.
What does delta neutral mean?
A portfolio whose total delta is near zero, so small price moves in the underlying barely change its value. It must be rebalanced as delta shifts.
Is delta the probability of finishing in the money?
Only as a loose rule of thumb. The real probability differs, especially for longer-dated options and in volatile markets.
Related terms
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