3 Month Rolling Pivot Table

[hbuzz]

Hi there,

I'm trying to create a pivot table to report on average values by month as a 3 month rolling figure. My real data is approx 4000 rows x 80 columns. I have data for the past 18 months. What I want my pivot table to report on is the average of the last 3 months i.e.

March 2017 should include March, February, January
February 2017 should include February, January, December 2016
January 2017 should include January, Dec 2016, Nov 2016

Importantly rather than group these in the pivot table I need to report on the rolling figure so all months are detailed as opposed to grouping them.

I've attached a very simple file which represents the layout and the figures I'd expect the pivot to output.

Any help or ideas would be appreciated!