Calendar (or date) table is crucial for performing date intelligence calculations in Power BI.
Normally, you would find a reasonable calendar table in most data models. But occasionally I come across models where there is no calendar table.
So I present to you, the ultimate & best way to generate calendar table using Power Query.
How to create the perfect calendar table with Power Query?
Start by creating a new “blank query” connection in Power BI.
Then use the =List.Dates() function to generate the dates you want.
For example, to get the calendar dates for year 2025 use below code:
= List.Dates(#date(2025,1,1),365, #duration(1,0,0,0))
This will generate a list of all the dates in 2025.
Now, convert the list to a table using the List Tools > Transform ribbon.
Once you have the dates in a table format, you can use the “add column” ribbon and “Date” options to introduce many date related columns.
For example you can add:
- Year (4 digit year value)
- Month number
- Month name
- Weekday name
- Weekday number
- Start of month
- End of month
- Start of week
- Quarter of the year
- Days in a month
Additional "smart" date columns
Apart from all the columns above, I normally add these two columns to my calendar tables.
- Year month (a 6 digit representation like 202308 for ex.)
- Type of month (current month, previous month, next month)
Let’s look at the Power Query (M) code for these columns.
Year Month (yyyymm):
= Table.AddColumn(#"Inserted Start of Month", "Year Month", each [Year] * 100 + [Month])
Type of Month:
= Table.AddColumn(#"Added Custom", "Month Type", each if Date.IsInCurrentMonth([Date]) then "This Month"
else if Date.IsInPreviousMonth([Date]) then "Previous Month"
else if Date.IsInNextMonth([Date]) then "Next Month"
else "Other Month")
Full M Script for generating the 2025 calendar table
Use this M script to generate the calendar table for year 2025.
To apply this, create a blank query in PQ and then go to View > Advanced Editor and paste the code there. Adjust the year in source step (step 1) to get the calendar for any year.
let
Source = List.Dates(#date(2025,1,1),365, #duration(1,0,0,0)),
#"Converted to Table" = Table.FromList(Source, Splitter.SplitByNothing(), null, null, ExtraValues.Error),
#"Renamed Columns" = Table.RenameColumns(#"Converted to Table",{{"Column1", "Date"}}),
#"Changed Type" = Table.TransformColumnTypes(#"Renamed Columns",{{"Date", type date}}),
#"Inserted Year" = Table.AddColumn(#"Changed Type", "Year", each Date.Year([Date]), Int64.Type),
#"Inserted Month" = Table.AddColumn(#"Inserted Year", "Month", each Date.Month([Date]), Int64.Type),
#"Inserted Month Name" = Table.AddColumn(#"Inserted Month", "Month Name", each Date.MonthName([Date]), type text),
#"Inserted Day of Week" = Table.AddColumn(#"Inserted Month Name", "Day of Week", each Date.DayOfWeek([Date]), Int64.Type),
#"Inserted Day Name" = Table.AddColumn(#"Inserted Day of Week", "Day Name", each Date.DayOfWeekName([Date]), type text),
#"Added Conditional Column" = Table.AddColumn(#"Inserted Day Name", "Is Weekend?", each if [Day of Week] = 6 then "Yes" else if [Day of Week] = 0 then "Yes" else "No"),
#"Inserted Start of Month" = Table.AddColumn(#"Added Conditional Column", "Start of Month", each Date.StartOfMonth([Date]), type date),
#"Added Custom" = Table.AddColumn(#"Inserted Start of Month", "Year Month", each [Year] * 100 + [Month]),
#"Added Custom1" = Table.AddColumn(#"Added Custom", "Month Type", each if Date.IsInCurrentMonth([Date]) then "This Month"
else if Date.IsInPreviousMonth([Date]) then "Previous Month"
else if Date.IsInNextMonth([Date]) then "Next Month"
else "Other Month")
in
#"Added Custom1"
Perfect Calendar with Power Query - Video
Check out this video to understand the process better.
How to customize the Calendar Query for other years?
You can change the “Source” step and replace the year number or number of days to generate the calendar for whatever year you need. For example, to make the 2 years calendar for years 2026 and 2027, use this code:
= List.Dates(#date(2026,1,1),730, #duration(1,0,0,0))
To make the calendar for next “n” years:
We can use additional date functions in Power Query M language to generate the calendar for next “n” years from a start date. For example, if you change the source step to below code, you will get next 5 years calendar from 1-Jan-2025.
= let start_date = #date(2025,1,1), number_of_years = 5, end_date = Date.AddYears(start_date,number_of_years), total_days = Duration.Days(end_date - start_date)
in List.Dates(start_date,total_days, #duration(1,0,0,0))
More ways to make the calendar table
Check out below tutorials from other Power BI / Excel folks to see different Power Query scripts.
8 Responses to “What is LAMBDA? 4 Practical examples to REALLY understand it”
Thanks so much for this, it's utterly brilliant!
Silly question - I assume LAMDA will work with dynamic arrays?
Very much so. Many of the new functions like MAP only make sense in the context of dynamic arrays and Lambda functions.
As usual, very informative material. Easy to understand and apply!
Thanks for making everyone awesome!
Easy to understand Lambda function through this tutorial. Thanks Chandoo.
I have Officce 365 (updated), but I can't see LAMBDA function. 🙁
I dont see "Office Insider" option in my excel 365.
Another option for First Monday...
=LAMBDA(anydate,WORKDAY.INTL(EOMONTH(anydate,-1),1,"0111111"))
Loving the binary options in WORKDAY.INTL David...