Running Value for each column based on the previous column Value

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("TZA7DkMhDATvQo308A9MnxOkRRSvyA1yf8WQ2KHZYpZFA2Okx/1+pZyesALTzCPphf3CgmIImC0r78Koc23Nslt+C4pB6Zblh9kxIxxYHGMrB1bHBHrgkCE5T0MJmfNuAMdCe+PuEPKEdZlmIfXub0Swuwqxq7FTXF0T/414NWasa0cZTGbODw==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Column1 = _t, Column2 = _t, Column3 = _t]),
    #"Promoted Headers" = Table.PromoteHeaders(Source, [PromoteAllScalars=true]),
    #"Changed Type" = Table.TransformColumnTypes(#"Promoted Headers",{{"Date", type date}, {"R1", Int64.Type}, {"R2", Int64.Type}}),
    #"Added Custom" = Table.AddColumn(#"Changed Type", "Custom", (k)=> let t = Table.SelectRows(#"Changed Type",each [Date]<=k[Date])
in 
13749 - List.Sum(t[R1]) - List.Sum(t[R2])
,Int64.Type)
in
    #"Added Custom"

How to use this code: Create a new Blank Query. Click on "Advanced Editor". Replace the code in the window with the code provided here. Click "Done". Once you examined the code, replace the entire Source step with your own source.