Quote from jenek-cowboy:
okey...But i really don't understand why i must put the IV to the model to get the theori price which i get from the same model????? I am assured that the calculeting the IV is a independent method...
Let's put it this way. The parameters that you need to input into an option pricing model are:
- price of underlying
- strike price
- time to expiry
- risk free interest rate
- dividends
- volatility
The volatility is the estimated future volatility.
Without the volatility parameter you cannot calculate the theoretical option price.
Now, all of the above 6 parameters are either fixed or easily observable with the exception of volatility. Volatility is the only parameter that is unknown and is not fixed.
So, the idea behind implied volatility is that you have the first 5 parameters and you can also observe the option price in the market. Hence, the only unknown that remains is the volatility. Therefore, you use the known 5 parameters and the market option price to find the volatility that equates to that option price. This is called implied volatility because it is the volatility that is implied in the market option price. That's it, this is where the implied volatility concept ends.
Estimating what the correct volatility number to put into a pricing model, i.e. estimating future volatility that you believe is correct, is a completely different matter. Some use statistical volatility (aka histrical volatility), others use past levels of implied volatility, yet others use some volatility modelling methods such as GARCH, and some use a combination of any of the above.
As a side note, you don't seem to understand the difference between implied volatility and a volatility number that you use in an option pricing model to find the theoretical option price.
I've tried my best to explain to you the concepts, but you seem to miss the point completely. I don't know, maybe is the language barrier!?