Try something like:

AVERAGE(M2:OFFSET(M2,0,-12))

where M2 contains the data for the last month in the target period.

--

Vasant


"Spartacus" wrote in message
...
I have data laid out as shown below:

Jan-04 Feb-04 --------- --------- --------- Jan-05 Feb-05
6,942.0 6,721.0 --------- --------- --------- 7,605.0 7,171.0

What I'm trying to do is have Excel calculate the 13 Month average for
each
row of data - for example, if the current month is Jan-05 then the desired
result would be to sum the values from Jan-05 through Jan-04 and divide by
13. The "Month-Yr" column labels are formatted exactly as they appear
above.

Can someone help solve this? Any assistance provided would be greatly
appreciated. Thanks.