Rolling of last 3 months

[capriconuser]

I am trying to take average of last months based on ration ie.

If jan month then amount of jan months as it is come because there is no past years.. if feb then this should be jan and feb 

i tried this 

sum( aggr( rangesum( above( sum(((BookAmount/Rev)/3)),0,3) ),Month))

[Gysbert_Wassenaar]

Try:

avg( aggr( rangeavg( above( sum(BookAmount/Rev),0,3) ),Month))

[Brett_Bleess]

Did Gysbert's expression work for you?  If so, do not forget to return to your thread and use the Accept as Solution button on his post to give him credit for the help and let other Members know this worked.  If you are still working upon things, please leave an update, it is appreciated to not leave threads unsolved if possible, so if Gysbert's suggestion did work, please mark it, or let us know it worked, and I can mark it for you.

Regards,
Brett