Option Greeks measure how an option’s price responds to different market factors, such as changes in the underlying stock price, time decay, and implied volatility.
Here is a breakdown of how Delta and Theta work, along with the two other primary Greeks every beginner should understand.
1. Delta ($\Delta$): Sensitivity to Stock Price
Delta measures how much an option’s premium is expected to change for every $1.00 move in the underlying stock, assuming other factors remain unchanged.
Call Options: Typically have a positive Delta between $0.00$ and $+1.00$. If a call has a Delta of $0.50$, its premium may increase by approximately $0.50 if the stock rises by $1.00$.
Put Options: Typically have a negative Delta between $-1.00$ and $0.00$. If a put has a Delta of $-0.30$, its premium may increase by approximately $0.30 if the stock falls by $1.00$.
Probability Indicator: Traders sometimes use Delta as a rough indicator of the probability that an option will expire in-the-money (ITM). However, Delta should not be treated as an exact probability.
2. Theta ($\Theta$): Sensitivity to Time Decay
Theta measures how much an option’s value is expected to decrease each day due to the passage of time, assuming other factors remain unchanged.
Works Against Option Buyers: Because options have a fixed expiration date, their time value generally decreases as expiration approaches. If an option has a Theta of $-0.05$, its premium may lose approximately $0.05 per share ($5.00 total) in one day, assuming other factors remain constant.
Decay Accelerates: Time decay is not linear. It generally becomes more significant as an option gets closer to expiration, particularly for short-dated options.
Seller’s Advantage: Theta generally works in favor of option sellers because the passage of time can reduce the value of the options they have sold. However, option selling can involve substantial risk.
Summary of Other Essential Greeks
To complete the picture, two other important Greeks influence option pricing:
Gamma ($\Gamma$): Measures how quickly an option’s Delta changes for every $1.00 move in the underlying stock. It helps show how rapidly an option’s sensitivity to price movement can change.
Vega ($\nu$): Measures how much an option’s premium is expected to change for a 1 percentage-point change in Implied Volatility (IV). When IV rises, option premiums generally increase for both calls and puts, while falling IV can put downward pressure on premiums.