Acumulative Totals suming previous row

source

code

let
    Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
    fx = (tbl) => 
        [lst = List.Buffer(Table.ToRows(tbl)),
        excess = tbl[Total to Allocate]{0} - List.Sum(tbl[Store Needs]),
        gen = List.Generate(
            () => 
                [
                    i = 0, 
                    alloc = List.Min({lst{0}{2}, lst{0}{3}}), 
                    stock = lst{0}{3} - alloc
                ],
            (x) => x[i] < List.Count(lst),
            (x) => 
                [
                    i = x[i] + 1, 
                    alloc = List.Min({lst{i}{2}, x[stock]}),
                    stock = x[stock] - alloc
                ],
            (x) => lst{x[i]} & {x[alloc], if x[i] = List.Count(lst) - 1 then excess else 0}
        )][gen],
    group = Table.Group(
        Source, 
        "Product", 
        {"x", fx}
    ),
    tbl = Table.FromRows(List.Combine(group[x]), Table.ColumnNames(Source) & {"Allocated", "Excess/Missing"})
in
    tbl

 result