Options Theta Decay Calculator
Calculate and visualize how time decay impacts your options premiums.
How to Use the Options Theta Decay Calculator
- Input Stock & Strike Price: Enter the current market price of the stock and the strike price of the option.
- Set Expiration & Volatility: Input the number of days until the option expires and the annualized implied volatility percentage.
- Configure Rates: Adjust the risk-free interest rate if needed (default is 5%).
- Analyze Results: View the instant calculation for Theta (daily decay) and the interactive chart showing how the option's time value erodes as expiration approaches.
What is Theta Decay?
Theta (Θ) measures the rate at which an option loses value as time passes. This phenomenon is known as "time decay." Options are wasting assets, meaning their value erodes daily as they approach expiration.
Theta is typically negative for long option positions (buyers) and positive for short option positions (sellers). The rate of decay is not linear; it typically accelerates rapidly in the final 30 days before expiration, as visualized in our calculator chart.
Why is Theta Important?
Understanding theta is critical for options traders because time is constantly working against buyers and in favor of sellers. If you buy an option and the stock price stays flat, you will lose money every day due to theta decay.
Frequently Asked Questions
Why does Theta decay accelerate?
Theta decay accelerates as expiration approaches because there is less time for the option to move in-the-money. The external or 'time value' portion of the option's price evaporates faster in the final weeks and days.
Is Theta always negative?
For long option positions (calls and puts), Theta is almost always negative, meaning you lose value over time. For short positions, Theta is positive, meaning you gain value as time passes.
How is Theta calculated?
Theta is calculated using the Black-Scholes model, taking into account the stock price, strike price, time to expiration, volatility, and interest rates. It represents the dollar amount an option's theoretical price will decrease in one day.