Formula Help to Calculate Quarterly Results

I need a formula to calculate the quarterly sales of a product based on the current month plus 2 previous months

Cell A3 indicates the current month formatted as mmm
Column A is the product starting at A5
Columns B - M are the sales by month, starting at B5 for Jan, C5 for Feb etc

What is the formula I need in cell O5 to give me the quarterly sales based on the value in cell A3

eg if the value in cell A3 is Mar the formula should add the sales in cell B5:D5, if the value in A3 is changed to Jun the formula should add the sales in cells E5:G5 etc

Thanks in advance for any help

Originally Posted by daddylonglegs

If A3 is a date formatted as mmm try

=SUM(OFFSET(B5:D5,,MAX(0,MONTH(A3)-3)))

Thanks daddylonglegs that worked a treat, have a similar thing in another spreadsheet where the month in the cell is formatted as text eg JAN, how would the above formula have to be changed to work in that scenario?

Originally Posted by daddylonglegs

In that case, assuming the same references as for your previous example but with months, e.g. "Jan", "Feb" etc. in B4:M4

=SUM(OFFSET(B5:D5,,MAX(0,MATCH(A3,B4:M4,0)-3)))

Thanks again