The Greeks: Delta
The most important number in options — what it means for your trades
What Is Delta?
Delta measures how much an option's price changes when the underlying stock moves $1. A call option with a delta of 0.50 will gain approximately $0.50 in value for every $1 the stock rises. Conversely, it will lose $0.50 for every $1 the stock falls.
Think of delta as a speedometer for your option. It tells you how sensitive your option's price is to movements in the stock.
Delta Values Explained
Call options have positive delta (0 to +1.00). As the stock goes up, call values go up. Put options have negative delta (0 to -1.00). As the stock goes up, put values go down.
An at-the-money (ATM) option typically has a delta around 0.50 for calls or -0.50 for puts. Deep in-the-money options have deltas approaching 1.00 (or -1.00 for puts), meaning they move almost dollar-for-dollar with the stock. Far out-of-the-money options have deltas close to 0, barely responding to stock movements.
Real Example
Consider AAPL trading at $189.20. A $190 call (nearly ATM) might have a delta of 0.48. This means if AAPL rises $1 to $190.20, the option price increases approximately $0.48. If you paid $3.00 for the option, it would now be worth roughly $3.48.
A deep ITM $170 call might have a delta of 0.92 — it moves almost like owning the stock itself. A far OTM $220 call might have a delta of only 0.08 — it barely budges when the stock moves.
Delta as Probability
One of the most practical uses of delta is as a rough probability estimate. A delta of 0.30 suggests roughly a 30% chance the option expires in-the-money. This is why covered call sellers often look for delta when choosing strikes — selling a 0.20 delta call means there is approximately an 80% chance you keep your shares.
This probability interpretation is not exact, but it is a widely used rule of thumb that helps you quickly gauge risk.
Key Terms
Delta — Rate of change of option price per $1 move in the stock
Gamma — Rate of change of delta itself (how fast delta accelerates)
ATM (At the Money) — When the strike price equals the current stock price
ITM (In the Money) — When a call's strike is below the stock price (or a put's strike is above)
OTM (Out of the Money) — When a call's strike is above the stock price (or a put's strike is below)