Using vlookup in a SUM funtion

[kc_native]

I am trying to come up with a formula to adjust the sum range in a SUM function, depending on the month of the year that I reference using a vlookup. The following is my first stab at it, but Excel doesn't like it. Any help would be appreciated.

=SUM(C13:C & (vlookup(M2,AA5:AB16,2,0)+12))/SUM(B13:B24)
 
AA5:AB16 looks like this:
 
Month   Fiscal Month
Oct             1
Nov             2
Dec             3
etc., etc.
 
M2 contains the current month of the year.

 

[Andrew Poulsom]

A couple of possibilities:

=SUM(C13:INDEX(C13:C24,VLOOKUP(M2,AA5:AB16,2,0)))/SUM(B13:B24)

=SUM(INDIRECT("C13:C"&(VLOOKUP(M2,AA5:AB16,2,0)+12)))/SUM(B13:B24)

 

[kc_native]

A couple of possibilities:

=SUM(C13:INDEX(C13:C24,VLOOKUP(M2,AA5:AB16,2,0)))/SUM(B13:B24)

=SUM(INDIRECT("C13:C"&(VLOOKUP(M2,AA5:AB16,2,0)+12)))/SUM(B13:B24)

Thanks, Andrew!