Dax Function: STARTOFMONTH
Category: Time Intelligence Functions
The STARTOFMONTH function in Power BI is a DAX time intelligence function that returns the first date of the current month within the context of a given date column. This function is often used in time-based calculations, particularly when summarizing or comparing data at the start of specific months.
Purpose of the Function
The primary purpose of STARTOFMONTH is to identify and extract the first date of a specified month based on the context. It is used to:
- Simplify calculations that require the beginning of the month.
- Provide an anchor date for comparisons or cumulative calculations.
- Support reports that need month-based grouping or filtering.
Type of Calculations
- Anchor Point Calculations: Identify the starting date for time series operations.
- Monthly Aggregations: Calculate metrics specific to the first date of each month.
- Comparative Analysis: Compare data from the start of different months.
Practical Use Cases
- Cumulative Sales Tracking: Calculate total sales from the start of the month to the current date.
- First Day Revenue: Determine revenue on the first day of each month for trend analysis.
- Date-Based Grouping: Use as a reference point for monthly grouping in dashboards.
STARTOFMONTH(<dates>)
| Parameter | Type | Description |
|---|---|---|
dates | Column | A column containing date values, typically from a well-structured date table. |
How Does STARTOFMONTH Dax Function Works
- Filter Context: The function evaluates the filter context for the given
datescolumn to identify the relevant month. - First Date Extraction: It retrieves the earliest date for that month based on the date column.
- Output Table: The result is a single-row table containing the first date of the identified month.
For example, if the dates column contains entries for April 2025 and the filter context applies April, STARTOFMONTH will return April 1, 2025.
What Does It Return?
The STARTOFMONTH function returns a single-column table containing one row of the earliest date in the current filter context for the specified month.
When Should We Use It?
- Anchor Date for Measures: Use it as a reference date for calculating month-to-date metrics.
- Comparison Across Months: Ideal for comparing metrics at the start of different months.
- Monthly Trends Analysis: Identify patterns or behaviors specific to the first date of each month.
Examples
Basic Usage
First Date of Month = STARTOFMONTH(Dates[Date])
This returns the first date of the current month within the filter context.
Column Usage:
Cumulative Sales =
CALCULATE(
SUM(Sales[Amount]),
Dates[Date] >= STARTOFMONTH(Dates[Date])
)
This calculates cumulative sales starting from the first day of the month to the current date.
Advanced Usage
Revenue Growth Start of Month =
DIVIDE(
CALCULATE(SUM(Sales[Revenue]), STARTOFMONTH(Dates[Date])),
CALCULATE(SUM(Sales[Revenue]), SAMEPERIODLASTYEAR(STARTOFMONTH(Dates[Date])))
)
This calculates the revenue growth from the start of the month compared to the same period last year.
Tips and Tricks
- Ensure a Complete Date Table: For accurate results, your date table should have a continuous and complete range of dates.
- Combine with Other Time Intelligence Functions: Use with
SAMEPERIODLASTYEARorENDOFMONTHfor more complex calculations. - Be Context-Aware: The function’s output depends on the filter context; ensure the context is correctly set.
Potential Pitfalls:
- The function returns a table, not a scalar value. Use it only in expressions or calculations that can handle table results.
Performance Impact of STARTOFMONTH DAX Function:
- Optimized for Indexing: Works efficiently when used with indexed date columns.
- Avoid Nested Calls: Redundant nesting of time intelligence functions can slow down performance.
Related Functions You Might Need
ENDOFMONTH: Returns the last date of the current month.STARTOFYEAR: Returns the first date of the year in the current filter context.FIRSTDATE: Returns the first date in the filter context without limiting it to months.DATEADD: Shifts dates by specified intervals, such as months or years.
Want to Learn More?
For more information, check out the official Microsoft documentation for STARTOFMONTH. You can also experiment with this function in your Power BI reports to explore its capabilities.
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It returns the first date of the current month within the filter context of a date column.
No, the function uses calendar months. To work with fiscal months, customize your date table accordingly.
It returns a single-row table containing the first date of the month.
STARTOFMONTH is specific to months, while FIRSTDATE returns the first date of any filter context.
It’s possible but not recommended. A properly configured date table ensures accuracy.
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