You use the Tab key or mouse to select each successive item to be entered. The underlying Javascript will calculate the value of the option. The equations governing the computation are shown. C is the value of the option, the number we are calculating. S is the price of the underlying Stock or commodity which the option covers.
L is the Strike price, the price at which the option owner can buy stock when the option matures.
The parameter r, rate per year, is the annualized rate of return for a risk free portfolio. Since the standard normal function is not available in Javascript, an approximation formula was used. You should compare numerical results from this model against others that are available on the net. Using the pop down list of links, under References , you can download any of the models and use them to calculate options. Since the calculation is in Javascript, the sourcecode for the program can be read using your browser.