This is a free spreadsheet that downloads free historical stock data from the Yahoo database into the spreadsheet and calculates the historical or realized volatility of the selected stock. The standard deviation of prices are plotted along side the stock price chart. The user can freely change the stock used by entering the ticker symbol into the appropriate field and perform a fresh download. Users are also able to change the date range used for the stock data, the number of days back to use for the volatility calculation and the number of volatility days to use.

Historical Volatility is a statistical calculation that tells option traders how rapid price movements have been over a given time frame. The most common method of calculating historical volatility is called the Standard Deviation.

Standard Deviation measures the dispersion of a set of data points from its average. The more disperse (spread out) the data is, the higher the deviation. This deviation is referred by traders as volatility.

Don't get too caught up in trying to understand the how's and whys of the standard deviation, just accept that all traders use this method for determining historical volatility.