Step 1: Insert a custom field Duration1 to your View. This column will have a formula that subtracts the task finish from the project start date Step 2: Right the column. Select Custom Fields. Select Formula and enter the formula ProjDateDiff([Project Start],[Finish]). http://i.imgur.com/wECRYzH.png Step 3: Default units of Duration is days. Select File backstage, Options, Schedule. Change the “Duration is entered in” to months.