Power BI has some built-in, easy-to-use DAX functions to get the Day of Month and Day of the week, but nothing for Day of Year and Day of the quarter. These calculations, however, are very simple and easy to implement using other functions. This short blog and video explain a method to calculate those for Power BI.
Day of Year
One simple way of calculating Day of Year is to get the date difference of that date with the starting day of that year. Here is how it works:
Day of Year = DATEDIFF(STARTOFYEAR('Date'[Date]),'Date'[Date],DAY)+1
This code will give us the day number of year for a give date. ‘Date'[Date] means the column named “Date” under the table named “Date”.
Day of Quarter
You can use the same method and get the date difference of the given date with the starting date of that quarter.
Day of Quarter = DATEDIFF(STARTOFQUARTER('Date'[Date]),'Date'[Date],DAY)+1
Days until the end of the quarter
If you compare with end of the quarter, then you get the number of days remained from the quarter.
Days until the end of the quarter = DATEDIFF('Date'[Date],ENDOFQUARTER('Date'[Date]),DAY)
Days until the end of the year
The calculation for counting the number of days until the end of the year is as below;
Days until the end of the year = DATEDIFF('Date'[Date],ENDOFYEAR('Date'[Date]),DAY)
Day of Month and Day of Week
For the day of Month and Day of week, you don’t need a custom expression, the DAY function will give you the day of month, and WeekDay will give you the day of week (with the ability to set the start date of the week).
Power Query Functions
These calculations can be done also in Power Query. If you are using the calculation in a dynamic DAX measure, then the calculations above would help. But if you need them to be added as a column or a pre-calculated expression, then I suggest doing it in Power Query.