How Option Prices are Determined

There are 5 components that determine the value of an option:

1.    The price of the underlying stock

2.    The strike price of the option

3.    The time until the option expires

4.    The cost of money (interest rates less dividends, if any)

5.    The volatility of the underlying stock 

The first four components are easy to figure out.  Each can precisely be measured.  If they were the only components necessary, option pricing would be a no-brainer.  Anyone who could add and subtract could figure it out to the penny.

The fifth component – volatility – is the wild card.  It is where all the fun starts.  Options on two different companies could have absolutely identical numbers for all of the first four components and the option for one company could cost double what the same option would cost for the other company.  Volatility is absolutely the most important (and elusive) ingredient of option prices.

Volatility is simply a measure of how much the stock fluctuates.  So shouldn’t it be easy to figure out?   It actually is easy to calculate, if you are content with looking backwards.  The amount of fluctuation in the past is called historical volatility.  It can be precisely measured, but of course it might be a little different each year.  

So historical volatility gives market professionals an idea of what the volatility number should be.  However, what the market believes will happen next year or next month is far more important than what happened in the past, so the volatility figure (and the option price) fluctuates all over the place based on the current emotional state of the market.