Number of Months between two dates

A work in progress, but maybe will help some:

let
    Source = Csv.Document(File.Contents("C:\temp\powerbi\months.csv"),[Delimiter=",", Encoding=1252]),
    #"Promoted Headers" = Table.PromoteHeaders(Source),
    #"Changed Type" = Table.TransformColumnTypes(#"Promoted Headers",{{"start", type date}, {"end", type date}}),
    #"Added Custom" = Table.AddColumn(#"Changed Type", "Years", each Number.RoundDown(Duration.Days(([end] - [start]) / 365.25),0)),
    #"Added Custom1" = Table.AddColumn(#"Added Custom", "Days Left", each Number.Mod(Duration.Days(([end] - [start])),365.25)),
    #"Added Custom2" = Table.AddColumn(#"Added Custom1", "StartMonth", each Date.Month([start])),
    #"Added Custom3" = Table.AddColumn(#"Added Custom2", "EndMonth", each Date.Month([end])),
    #"Added Custom4" = Table.AddColumn(#"Added Custom3", "Months", each [Years]*12 + ([EndMonth] - [StartMonth]))
in
    #"Added Custom4"

startendYearsDays LeftStartMonthEndMonthMonths

Need to fix that middle row obviously.