Power Query | Create Column out of two dates

Laurent500 

The real challenge in your scenario is to calc. the #Months between [Start Date] and [End Date] as PQ currently doesn't have a function like Duration.Months or an equivalent to Excel/Dax https://docs.microsoft.com/en-us/dax/datediff-function-dax. I'm not aware of a perfect solution to this (One on the Net "claims" he figured it out but there are situations where his function doesn't return the correct #Months) ==> In the below query adjust AvgDaysPerMonth at your convenience

With https://docs.microsoft.com/en-us/powerquery-m/list-accumulate in attached sample:

(can be shortened)

let
    Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
    ChangedTypes = Table.TransformColumnTypes(Source,
        {{"Project", type any}, {"Budget", type number}, {"Start Date", type date}, {"End Date", type date}}
    ),
    AvgDaysPerMonth = 365/12,
    CalcMonths = Table.AddColumn(ChangedTypes, "Months", each
        Number.RoundUp(
            (Duration.Days(Date.EndOfMonth([End Date]) - Date.StartOfMonth([Start Date])) +1) / AvgDaysPerMonth,
            0
        ), Int64.Type
    ),
    MaxMonths = List.Max(CalcMonths[Months]),
    EarliestStart = Date.StartOfMonth(List.Min(CalcMonths[Start Date])),
    MonthsList = List.Transform({0..MaxMonths}, each Date.AddMonths(EarliestStart, _)),
    AddedMonths = List.Accumulate(MonthsList, CalcMonths,
        (accum,current) as table => Table.AddColumn(accum, Date.ToText(current,"MMM yyyy"), each
            if (Date.StartOfMonth([Start Date]) <= current) and ([End Date] >= current)
            then [Budget] / [Months]
            else null,
            type nullable number
        )
    ),
    RemovedMonths = Table.RemoveColumns(AddedMonths,{"Months"})
in
    RemovedMonths