Your Velocity & Sensitivity Gauge
Delta measures how sensitive your option's price is to a $1.00 move in the underlying stock. Think of it as the velocity of your position.
If a stock moves $1.00 and your call option has a 0.50 Delta, your option price should theoretically increase by $0.50. It's the first-order derivative of price, showing you the immediate impact of a price change.
If you buy a put, you have negative delta (you want the stock to go down). However, if you sell (short) a put, you are "shorting a negative." This gives you positive delta. When you sell a put, you are essentially "bullish"—you want the stock to stay above your strike or rise.
If you buy a call (+0.50 Delta) and buy a put (-0.50 Delta) with the same expiration, your Net Delta is 0. This is called being "Delta Neutral." You don't care which way the stock moves; you are simply betting that the size of the move will be larger than the premium you paid.
If you have a total portfolio Delta of +250, you are making or losing money at the same rate as someone owning 250 shares of the stock. You can "hedge" this by selling calls or buying puts to bring that number closer to zero if you become bearish.
Delta is a great "Probability of Profit" (POP) proxy. A 16-delta out-of-the-money (OTM) put has roughly an 84% chance of expiring worthless. Traders often sell these "low-delta" options to collect high-probability income.
One of the most powerful things about Delta is that you can add different positions together to see your "Net Delta." This helps you understand your overall market exposure across all positions.