Need to generate a column with the first day of the week listed in each row

[jbuck2020]

I have a table that looks like this with weeks starting on Tuesday and ending on Monday:

Date	WeekNumber	Day of Week Number
10/17/2021	147	1
10/18/2021	147	2
10/19/2021	147	3
10/20/2021	147	4
10/21/2021	147	5
10/22/2021	147	6
10/23/2021	147	7
10/24/2021	148	1
10/25/2021	148	2
etc	etc	etc

I'm trying to generate a new column that shows the date from day 1 column above on each row.

Date	WeekNumber	Day of Week Number	WeekStartDate
10/17/2021	147	1	10/17/2021
10/18/2021	147	2	10/17/2021
10/19/2021	147	3	10/17/2021
10/20/2021	147	4	10/17/2021
10/21/2021	147	5	10/17/2021
10/22/2021	147	6	10/17/2021
10/23/2021	147	7	10/17/2021
10/24/2021	148	1	10/24/2021
10/25/2021	148	2	10/24/2021
etc

I've tried several dax calculations but they all seem to end in the following error message: "a single value for column "date" in table "Calendar" cannot be determined."

Any ideas why this might be happening and/or how to add this WeekStartDate column?

[AlexisOlson]

How about this as a calculated column?

WeekStart = Table1[Date] - Table1[Day of Week Number] + 1

[jbuck2020]

Still getting the "A single value for column 'Date' in table 'Calendar' cannot be determined. This can happen when a measure formula refers to a columnj that contains many values without specifying an aggregation such as min, max, count, or sum to get a single result." error

[AlexisOlson · Accepted solution]

The most likely reason is that you are trying to define a measure instead of a calculated column. You'll definitely get that error if you try to define a measure that way but not for a calculated column.

[jbuck2020]

That was it! Thanks!