This method of averaging the basis of mutual fund shares is no longer available.
At one time, the tax regulations offered two different methods for averaging the basis of mutual fund shares. The more complicated one, called the double-category method, maintained one average for shares with a short-term holding period and a separate average for long-term shares. This method was rarely used and has been discontinued. If you used the double-category method for any of your holdings, your basis for any shares sold on or after April 1, 2011 is determined by averaging together the basis of all the identical shares in the account, regardless of holding period.