How to get cumulative market share

[abc_18]

Hello everyone,

I have to calculate Cumulative Market Share.

 As of now, the formula which I am using it's just summing up, attached screen shot below.

=rangesum(above(sum({<Date={">=$(=YearStart(max(Date),0,4))<=$(=AddYears(MonthEnd(max(Date)),0))"}>}sales)
,0,RowNo()))
/
RangeSum(above(total sum({<Date={">=$(=YearStart(max(Date),0,4))<=$(=AddYears(MonthEnd(max(Date)),0))"}>}sales_aggr),0,RowNo()))

It should be as per the following

Cumulative Growth for Apr'20: (Sales Apr'20- Sales Apr'19)/ Sales Apr'19
Cumulative Growth for May'20: (Sales Apr+May'20- Sales Apr+May'19)/ Sales Apr+May'19

Cumulative Growth for X'20: (Sales Till X'20- Sales Till X'19)/ Sales Till X'19. where X is the month in the FY

@Vegar , @Gysbert_Wassenaar , @sunny_talwar  Please suggest.

Regards

[abc_18]

Can anyone please suggest on below topic?