You can use the following syntax in DAX to calculate the number of days in a month:

Days in Month = DAY(EOMONTH('my_data'[Date],0))

This particular formula creates a new column named **Days in Month** that contains the number of days in the month for the corresponding date in the **Date** column.

The following example shows how to use this syntax in practice.

**Example: How to Calculate Number of Days in Month in Power BI**

Suppose we have the following table named **my_data** that contains information about sales made on various dates by some company:

Suppose that we would like to create a new column that contains the number of days in the month associated with each date in the **Date** column.

To do so, click the **Table tools** tab, then click the icon called **New column**:

Then type the following formula into the formula bar:

Days in Month = DAY(EOMONTH('my_data'[Date],0))

This will create a new column named **Days in Month **that displays the number of days in the month for each corresponding date in the **Date** column:

For example, we can see:

- January 1, 2022 is in January, which has
**31**days in the month. - May 14, 2022 is in May, which has
**31**days in the month. - June 19, 2022 is in June, which has
**30**days in the month.

And so on.

**How This Formula Works**

Recall the formula that we used to calculate the number of days in the month:

Days in Month = DAY(EOMONTH('my_data'[Date],0))

First, we used the **EOMONTH** function to extract the last day of the month from the **Date** column.

For example, for a date of January 1, 2022 this function would return **January 31, 2022**.

Then, we used the **DAY** function to convert this date to a day of the month.

For example, for January 31, 2022 this function would return **31**.

We repeat this process for each date in the **Date** column.

**Note**: You can find the complete documentation for the **EOMONTH **function in DAX here.

**Additional Resources**

The following tutorials explain how to perform other common tasks in Power BI:

Power BI: How to Convert Date to Text

Power BI: How to Convert Date to Month and Year

Power BI: How to Convert Date to Quarter and Year