fn_cumulative_Total.M

// Code written by Hans Peter Pfister, www.powerbi-pro.com

(Input as table) =>

let
    Sorting = Table.Sort(Input,{{"Datum", 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, "Saldo", 
                                      each List.Sum(
                                                    List.Range(added_Index[Betrag],0,[Index])
                                                    )
                                      ),
    extract_total = cumulativ_total[Saldo]  	                            // transform new column into list as result for grouping
in
extract_total