Formula to find the header index of the first non blank cell of a range in Excel?

Question

I have this table, which can be seen as a basic custom gantt chart:

And I would like to fil

Answer 1

In A2 try this formula copied down

=IF(COUNTA(B2:Z2),INDEX(B$1:Z$1,MATCH(TRUE,INDEX(B2:Z2<>"",0),0)),"")

you may have to format column A with the required date format

assumes data up to column Z, adjust as required