Returns the start of month.
The name of a column containing dates or a one column table containing dates.
A table containing a single column and single row with a date value.
In order to use any time intelligence calculation, you need a well-formed date table. The Date table must satisfy the following requirements:
- All dates need to be present for the years required. The Date table must always start on January 1 and end on December 31, including all the days in this range. If the report only references fiscal years, then the date table must include all the dates from the first to the last day of a fiscal year. For example, if the fiscal year 2008 starts on July 1, 2007, then the Date table must include all the days from July 1, 2007 to June 30, 2008.
- There needs to be a column with a DateTime or Date data type containing unique values. This column is usually called Date. Even though the Date column is often used to define relationships with other tables, this is not required. Still, the Date column must contain unique values and should be referenced by the Mark as Date Table feature. In case the column also contains a time part, no time should be used – for example, the time should always be 12:00 am.
- The Date table must be marked as a date table in the model, in case the relationship between the Date table and any other table is not based on the Date.
The <Dates> argument can be any of the following:
- A reference to a date/time column. Only in this case a context transition applies because the column reference is replaced by
- A table expression that returns a single column of date/time values.
- A Boolean expression that defines a single-column table of date/time values.
STARTOFMONTH filters <Dates> into a 1-row, 1-column table that shows only the earliest date, in the entire <Dates> column devoid of all filters, that is in the same year and month as the earliest visible date in <Dates>.
The following STARTOFMONTH call
STARTOFMONTH ( 'Date'[date] )
is a more efficient implementation of the following semantically equivalent expression:
VAR FirstDateVisible = CALCULATE ( MIN ( 'Date'[Date] ) ) VAR FirstYearVisible = YEAR ( FirstDateVisible ) VAR FirstMonthVisible = MONTH ( FirstDateVisible ) VAR DaysInMonth = FILTER ( ALL ( 'Date'[Date] ), YEAR ( 'Date'[Date] ) = FirstYearVisible && MONTH ( 'Date'[Date] ) = FirstMonthVisible ) VAR FirstDayInMonth = MINX ( DaysInMonth, 'Date'[Date] ) VAR Result = CALCULATETABLE ( VALUES ( 'Date'[Date] ), 'Date'[Date] = FirstDayInMonth ) RETURN Result
Learn more about STARTOFMONTH in the following articles:
Other related functions are:
Contributors: Alberto Ferrari, Marco Russo, Jes Hansen
MSDN documentation: https://docs.microsoft.com/en-us/dax/startofmonth-function-dax