How much the contract moves for each dollar the stock moves. Call: between 0 and ++1 (positive). Put: between 0 and −−1 (negative). Also a rough indicator of the chance the contract finishes in the money.
How to read the number
Delta reads as a number between 0 and 1 for calls (Calls) and between 0 and −1 for puts (Puts). A Delta of 0.50 means the contract price moves about $0.50 for every $1 the stock moves. The deeper a contract goes in the money, the closer its Delta gets to 1 and the more it moves like the stock. The further out of the money it sits, the closer to zero, and the weaker its response.
Why this number matters
Delta answers two questions at once: how much do I make if the stock moves my way, and roughly how likely is the contract to finish in the money? The market treats a Delta of 0.30 as a rough estimate of a 30% probability. That is a reading convention, not a mathematical promise. The sum of your positions' Deltas also tells you your total directional exposure: a portfolio whose Deltas sum to zero is not directly affected by a small move in the stock.
Hypothetical example
A stock at $100 and a call with a $100 strike and a Delta of 0.50. The stock rises to $101: the contract price rises about $0.50. If the strike were $90 (deep in the money), the Delta would be about 0.90 and the contract would rise about $0.90 for the same move.
Common mistake
Reading Delta as a fixed number. Delta itself changes with the stock's move and with time, and the speed of that change is Gamma. Someone who buys a contract with a Delta of 0.30 and then sees the stock move their way may find the Delta has become 0.45, so gains accelerate. The reverse holds against them.
Where to see it on the platform
The options calculator shows Delta for every contract you price, and the gamma dashboard adds up dealer positioning derived from Delta and Gamma across the whole chain.
