Theta Erosion

Theta erosion is the daily reduction in an option's premium due to the passage of time. It is the cost paid by option buyers to the sellers for the potential of outsized returns.

The rate of erosion is non-linear and becomes most pronounced as the option approaches its expiration date. For sellers, theta erosion is a consistent source of potential profit, often referred to as "collecting theta." For buyers, it acts as a constant headwind that must be offset by favorable price movements or increases in implied volatility.

Understanding the mechanics of theta erosion is vital for structuring trades that align with a trader's time horizon and outlook. It is the primary engine of time-based trading strategies.