Time Decay

Time decay is the gradual decrease in the value of an option as time passes. This is because the option becomes less likely to be exercised as the expiration date approaches.

There are two main reasons for time decay:

* **The time value of money:** The longer you have to wait to receive a payment, the less valuable it is. This is because you could invest the money and earn interest in the meantime.
* **The increased probability of the underlying asset moving against you:** As the expiration date approaches, the probability of the underlying asset moving outside of the option's strike price increases. This means that the option is more likely to expire worthless.

The rate of time decay is determined by the following factors:

* **The underlying asset's volatility:** The more volatile the underlying asset, the faster the option will decay. This is because there is a greater chance that the asset will move outside of the option's strike price.
* **The time to expiration:** The longer the time to expiration, the slower the option will decay. This is because there is more time for the asset to move back into the option's strike price.
* **The interest rate:** The higher the interest rate, the faster the option will decay. This is because the opportunity cost of holding the option is greater.

Time decay can be a significant cost for option buyers, especially for long-term options. However, it can also be used to an advantage by option sellers, who can collect time decay as the option approaches expiration.

Here is an example of how time decay works:

Suppose you buy a call option on a stock that is currently trading at $50. The option has a strike price of $50 and expires in one year. The option premium is $5.

Over the next year, the stock price stays at $50. The option will expire worthless, and you will lose your $5 premium. This is because the option has no intrinsic value (the difference between the stock price and the strike price) and only has time value.

However, if the stock price had increased to $60, the option would have been worth $10 at expiration. This is because the option would have had $10 of intrinsic value (the difference between the stock price and the strike price) and no time value.

In this example, the time value of the option decayed from $5 to $0 over the course of one year. This is because the option became less likely to be exercised as the expiration date approached.

Time decay is an important concept to understand for anyone who is trading options. It can be a significant cost for option buyers, but it can also be used to an advantage by option sellers.