# Call option value and volatility

These bid and ask prices are not chosen at random. They are values based on a mathematical formula, such as the Black-Scholes model.

To that model, market makers may decide to add tweaks of their own that depend on the current risk or lack thereof of their positions. The point is that these prices are not chosen at random. The value of an option can be calculated exactly if you know the true number for each of the seven items that go into the equation. In reality, only six of these ways to value options are known, and the seventh volatility must be estimated.

The best anyone can do is to estimate that volatility, which in turn produces an estimated value for the option. Specifically the time period is between when the option is traded and expiration.

Stock price — Consider a call option. The higher the stock price the more a call option is worth. Similarly, the lower the stock price, the more a put option is worth. The lower the call stock price, the more a put is worth. Strike Price — The price at which the call owner may buy, and the put owner may sell, stock.

Thus, calls increase in value as the strike price moves lower. Time before expiration arrives — The more time, the more an option is worth. As the option owner, you want the stock to undergo a favorable move. In reality, only six of these ways to value options are known, and the seventh volatility must be estimated. The best anyone can do is to estimate that volatility, which in turn produces an estimated value for the option.

Specifically the time period is between when the option is traded and expiration. Stock price — Consider a call option. The higher the stock price the more a call option is worth. Similarly, the lower the stock price, the more a put option is worth.

The lower the call stock price, the more a put is worth. Strike Price — The price at which the call owner may buy, and the put owner may sell, stock. Thus, calls increase in value as the strike price moves lower. Time before expiration arrives — The more time, the more an option is worth. As the option owner, you want the stock to undergo a favorable move. The more time, the greater the possibility of that favorable move occurring.

Interest rates — This is a minor factor in the price of an option. As interest rates rise, call options increase in value. When investors buy calls instead of stock, they have extra cash not used to buy stock and that cash can earn interest.

When rates are higher, they earn more interest, and thus, are willing to pay more to own call options.