1
Create a combined lookup key
This joins the Salesperson and Month columns with a vertical bar. It is useful for matching rows or creating a unique label.
[Salesperson] & "|" & [Month]
Power Query support
Fix your Power Query custom column error.
A clear guide to joining Salesperson and Month values, then turning month names into valid dates without expression errors.
See the solution Beginner-friendly • Copy-ready formulas
Small syntax issue. Simple fix.
Follow the formula structure below.
Quick answer
Your #date formula starts with an opening parenthesis after #date, but it does not finish with a closing parenthesis. Add one ) after the final 1 to complete the function.
Step-by-step guide
Build the custom columns correctly
In Power Query, select Add Column → Custom Column, then paste the formula that matches your goal.
2
Use a cleaner version
Use this safer formula if names or month values may contain accidental spaces or non-printing characters.
Text.Clean(Text.Trim([Salesperson])) & "|" & Text.Clean(Text.Trim([Month]))Why the date formula errors
The #date function needs three values: year, month, and day. Your formula has all three values, but the opening bracket is never closed.
Corrected formula
Turn a month name into a 2025 date
= #date(2025,
if [Month] = "January" then 1
else if [Month] = "February" then 2
else if [Month] = "March" then 3
else if [Month] = "April" then 4
else if [Month] = "May" then 5
else if [Month] = "June" then 6
else if [Month] = "July" then 7
else if [Month] = "August" then 8
else if [Month] = "September" then 9
else if [Month] = "October" then 10
else if [Month] = "November" then 11
else 12,
1)Helpful checks
Before you click OK
Check spelling
Month text must match the formula exactly, including spelling and capitalization.
Keep a fallback
The final else 12 treats any unmatched value as December, so review your source data first.
Match every bracket
Whenever a function begins with (, make sure it ends with a matching ) after its final value.