convert to date format

Hi, mahoneypat 

You are absolutely right, obviously I am still not familiar with the PoweQuery language. It definitely saves a lot of steps.
But what confuses me is that in Excel it seems that the first day is January 1, 1900, and the result I get after converting the numbers to dates in Power BI indicates that the first day should be December 30, 1899, which is a little strange.
But your formula is definitely correct anyway. Thanks for sharing.

Anonymous  if you want to get result in Power Query, here is the improved M code:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMtY3MtU3MjAyVIrViVYyMTEyNgOzgOJGqOKWYBaYUFCKjQUA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Column1 = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Column1", type text}}),
    a = Table.AddColumn(#"Changed Type", "1899-12-30", each try Date.From([Column1]) otherwise Date.AddDays(#date(1899,12,30), Number.FromText([Column1])))//,
    //b = Table.AddColumn(a, "1900-1-1", each try Date.From([Column1]) otherwise Date.AddDays(#date(1900,1,1), Number.FromText([Column1])))
in
    a//b

Zerrick

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