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BLACK-SCHOLES OPTION PRICING MODEL


The Black-Scholes model prices the "fair value" of an option. Current "appropriate" value of an option is calculated on the basis of historical data and calculated probabilities of future stock prices. The basic formula is presented below:

Call Premium = Expected Future Stock Price - Expected Cost of Exercising Option


The Black-Scholes model adds the following adjustments to this formula:
· for the possibility of a range of future stock prices,
· for the net present value of the exercising cost,
· for the possibility that the exercise price may become higher than the underlying stock price, etc.
The option always costs more than the differential between the exercise price and current stock price. The difference exists because the future underlying stock value may be more or less than $100. If the underlying stock rises to $104, the call premium rises to more than $8. The cost of the option above and beyond the difference between the strike and the underlying stock price is what you pay for the possibility of a higher price. The Black-Scholes model quantifies the possible future underlying stock prices. 

No one knows the future value of a stock with certainty. The Black-Scholes model assumes a standard normalized distribution curve for future stock prices. The sigma calculation for this curve, which determines the height or width of the standard curve, is derived from historical stock data. The more volatile a stock has been, the higher probability it has of being far from today's price on expiration date. To be compensated for this, the seller needs to receive more for the option, and the buyer needs to pay more for the possibility.
Historical data is used to predict future stock prices. In this respect, Black-Scholes modeling has the same problems as technical analysis: the past doesn't always predict the future.

The Black-Scholes option model is primarily used to search for underpriced option to buy, or overpriced option to sell and to hedge a portfolio to reduce risk (lower volatility). Options can be sold to offset losses in the underlying stocks. 

The Black-Scholes model does have weak points. The model uses normal standardized probability curves for future stock price approximations. While they can be considered accurate at any given time of pricing, the model discounts prices with low probabilities. But the lower future price with a low probability may still turn out to be the future price. 

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