OK, if you want an average for each 3 month period:

Assuming:

A1:L1 = month names
A2:L2 = numeric values

Enter this formula in D3 and copy across to L3:

=IF(D2="","",AVERAGE(B2:D2))

If you want just a single rolling average:

=IF(COUNT(A2:L2)<4,"insufficient
data",AVERAGE(OFFSET(A2,,COUNT(A2:L2)-1,,-3)))

This assumes each month data will be entered from left to right and there
will not be any months where no data is entered.

--
Biff
Microsoft Excel MVP


"Kylie" wrote in message
...
Good point! It's a new reporting structure I am implementing so obviously
for the first 3 months the average won't be applicable.

"T. Valko" wrote:

What do you do in Jan, Feb and Mar when there aren't 3 preceding months?

--
Biff
Microsoft Excel MVP


"Kylie" wrote in message
...
Hi
Am wanting to determine a 3 month average based on the 3 months
proceeding
the current month.

The spreadsheet contains 12 months of data. If the current month is
determined elsewhere in the data on the spreadsheet, how can I use that
so
that I can determine the 3 month average for the months preceeding the
current month.
Eg

Current month = May

jan feb mar apr may june july aug sep oct nov dec
last
3
month avg
5 7 10 6 9
??

(based on feb mar apr)

When June comes around the 3 month average should then move to be based
on
Mar, Apr & May.

Any thoughts??