a

[amitchandak]

@SillySuzy , try like

Within90DaysPurchases =
var _max = calculate(Min(Sales[OrderDate]), filter(ALLSELECTED ( Sales ), Sales[CustomerKey] = MAX ( Sales[CustomerKey] ) ))
return
CALCULATE (
COUNTROWS ( Sales ),
filter( ALLSELECTED ( Sales ),
Sales[CustomerKey] = MAX ( Sales[CustomerKey] ) &&
Sales[OrderDate] > _max &&
Sales[OrderDate] < _max + 90
) )

[SillySuzy]

I appreciate your help, but I cant use Filter(), sadly.