Hi Paul, in that sample your table on the right doesn't have a row above so it's aonly doing the this part of the expression:
-Sum(TOTAL Aggr(Sum({<year, month>}[Amount]*-1), YearMonth))
Yo can try it leaving only this as expression, it only sums all the amounts... in a wird thing beacuse it shows the negative of a value multiplied by -1 wich can be simplified to:
Sum(TOTAL Aggr(Sum({<year, month>}[Amount]), YearMonth))
And if you want to work based in the (max) year and month selected:
Sum({$<year, month, date={'<=$(=Date(Max(date)))'}>}TOTAL Aggr(Sum({<year, month, date={'<=$(=Date(Max(date)))'}>}[Amount]), YearMonth))
For the last year you can sum all values until 12 months before the max date:
Sum({$<year, month, date={'<=$(=AddMonths(Max(date), -12))'}>}TOTAL Aggr(Sum({<year, month, date={'<=$(=AddMonths(Max(date), -12))'}>}[Amount]), YearMonth))
