Custom Column: End Of Last Month

[ivath0]

I want to use Power Query to calculate the number of days between the dates in a Dates column(A) and the end date of last month(B). Eg. Between: (A) 22/6/2020 and (B) 31/01/2021

[Vera_33]

Hi @ivath0 

You need the data type is Date, paste below M code in Advanced Editor of a blank query

let
Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WclTSUXJSitWJVjIy0jfTNzIwMgCKGBvqGxiCOIZKsbEA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Column1 = _t, Column2 = _t]),
#"Promoted Headers" = Table.PromoteHeaders(Source, [PromoteAllScalars=true]),
#"Changed Type1" = Table.TransformColumnTypes(#"Promoted Headers",{{"A", type date}, {"B", type date}}),
#"Added Custom" = Table.AddColumn(#"Changed Type1", "Custom", each Duration.Days(DateTime.Date(Date.EndOfMonth([B])) - [A]) - 1)
in
#"Added Custom"

[AlexisOlson · Accepted solution]

You could take the difference between the start of the current month and column A and subtract a day.

Duration.Days(DateTime.Date(Date.StartOfMonth(DateTime.LocalNow())) - [A]) - 1

[ivath0]

Thank you. That works.

And I tried Date.StartOfMonth(DateTime.LocalNow()) - 1) to give just the last date of last month. The syntax is passed but the column just shows errors. How do I correct the errors? And how do I see an explanation of the errors in Power BI?

[v-jingzhang]

@ivath0 

Use Date.AddDays to add or minus number of days.

Date.AddDays(DateTime.Date(Date.StartOfMonth(DateTime.LocalNow())),-1)

You can click the error cell to see the error message.

Regards,
Community Support Team _ Jing Zhang
If this post helps, please consider Accept it as the solution to help other members find it.