fn_cumulative_Total_en.M

// Code written by Hans Peter Pfister, www.powerbi-pro.com
let
    Source = (Input as table) =>

let
    Sorting = Table.Sort(Input,{{"Date", Order.Ascending}}),                                        // Sort table
    added_Index = Table.AddIndexColumn(Sorting, "Index", 1, 1),                                      // add Index, base 1
    cumulativ_total = Table.AddColumn(                                                               // add new column with running total 
                                            added_Index, "Total", 
                                            each List.Sum(
                                                         List.Range(added_Index[Amount],0,[Index])
                                                        )
                                            ),
    extract_total = cumulativ_total[Total]                                                           // transform new column into list as result for grouping
in
extract_total
in
    Source