Adding a +1 inside Date function results in an error but when adding +1 outside works fine, why?

Hi TallPolishAdam ,

I think the final two measures should be correct. 

In your first code, you add "- WEEKDAY([Date of Report], 2) + 1" in Date() function. Power BI will check whether year/month/day parts all correct, then return date value. So if day part return Negative numbers, Power BI will return error.

Week of Report =
DATE ( YEAR ( [Date of Report] ), MONTH ( [Date of Report] ), DAY ( [Date of Report] ) - WEEKDAY ( [Date of Report], 2 ) + 1 )

The final two measures, both add "- WEEKDAY([Date of Report], 2) + 1" outof date, so Power BI will do calculation on [Date of Report] and think "- WEEKDAY([Date of Report], 2) + 1" as days.

Best Regards,
Rico Zhou

If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.