Sales stage history - count

Hi,

I am trying to create a report showing the number or percentage of closed opportunities that have been in one specific stage previously. So, for example I have 5 sales stages, and I want to count the number of opportunities that are closed and that have been in sales stage 3.

I am creating a report on the Sales Stage History subject area, and have put a case statement on the sales stage history column (case when .. sales stage 3 then yes else no end). This works fine.

However, when I try to create my report, the opportunities that have been in sales stage 3 are counted twice. In one specific month, there are say 10 closed opportunities, out of which 4 have been in sales stage 3. I would expect to get a percentage of 40 / 60.