You can use the following formulas in DAX to get the first day of the week for a given date:

**Formula 1: Get First Day of Week (Assuming First Day is Sunday)**

Week Start = 'my_data'[Date] - WEEKDAY('my_data'[Date], 2)

**Formula 2: Get First Day of Week (Assuming First Day is Monday)**

Week Start = 'my_data'[Date] - WEEKDAY('my_data'[Date], 2) + 1

Both formulas create a new column named **Week Start** that contains the first day of the week for the corresponding date in the **Date** column.

The following example shows how to use both formulas in practice.

**Example: How to Get First Day of Week in Power BI**

Suppose we have the following dataset in Power BI that contains information about total sales made on various dates by some company:

Suppose that we would like to create a new column that contains the first day of the week for each corresponding date in the **Date** column of the table.

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

Then type the following formula into the formula bar:

Week Start = 'my_data'[Date] - WEEKDAY('my_data'[Date], 2)

This will create a new column named **Week Start** that contains the first day of the week (assuming the first day is considered **Sunday**) for each corresponding date in the **Date** column:

For example, we can see:

- The first day of the week for the date 1/8/2024 is
**1/7/2024**. - The first day of the week for the date 1/10/2024 is
**1/7/2024**. - The first day of the week for the date 1/13/2024 is
**1/7/2024**. - The first day of the week for the date 1/15/2024 is
**1/14/2024**.

And so on.

If you would like the first day of the week to be considered Monday instead, then you can type the following formula into the formula bar:

Week Start = 'my_data'[Date] - WEEKDAY('my_data'[Date], 2) + 1

This will create a new column named **Week Start** that contains the first day of the week (assuming the first day is considered **Sunday**) for each corresponding date in the **Date** column:

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

**Additional Resources**

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

Power BI: How to Filter Between Two Dates

Power BI: How to Extract Month from Date

Power BI: How to Extract Year from Date