Without knowing some specifics about your layout I can't give you a formula
example, but assuming your columns are Jan, Feb, Mar, etc I'd use something
like

=SUM(OFFSET(top_left_corner of PlanPax, A21,B4-2,1,3))

Duke

"Luke" wrote:

I have the following index formula '=INDEX(PlanPax,A21,$B$4)' where cell B4
is the month number e.g. 3 for March. How could I amend the formula (and cell
B4) so that I sum January to March (or columns 1 to 3)?

Luke