Ref: http://www.optionstradingsignals.com/understanding-implied-volatility-when-trading-options-part-1/ 1 Std Dev = 68% Probability 2 Std Dev = 95% Probability 3 Std Dev = 99% Probability This formula is fine for 1 Std Dev 1 Std Dev = Price x Volatility x SQRT( Calendar Days/ 365.25) 68% = Price x Volatility x SQRT( Calendar Days/ 365.25) ************* Question1: Whats the above formula for 2 Std Dev ? 95% = ??? Question2: Whats the above formula for any probability percentage ? 75% = ??? NOTE: I assume you dont change volatility to fit, as thats a fixed variable. Any ideas??? Thanks

Thanks.. got it.. But I cant seam to calculate the 1.152.. hows that worked out ? Please make as simple example

look in the spreadsheet. The numbers are for the ERF function http://en.wikipedia.org/wiki/Error_function