When you say "rolling", do you mean:

Case #1
1 to 12 - Jan to Dec
2 to 13 - Feb to Jan
3 to 14 - Mar to Feb

OR
Case #2
1 to 12 - Jan to Dec-04
13 to 24 - Jan to Dec-05
25 to 36 - Jan to Dec-06

With data in Column A:

Case #1
=AVERAGE(A1:A12)
And copy down as needed.

Case #2
=AVERAGE(INDEX(A:A,12*ROWS($1:1)-11):INDEX(A:A,12*ROWS($1:1)))
And copy down as needed.
--
HTH,

RD
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Please keep all correspondence within the Group, so all may benefit!
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"SamA" wrote in message
...
I am trying to create a 12 month rolling average, example follows.

J F M A M J J A S O N D average
item 1 2 3 4 5 6 7 8 9 10 11 12 (rolling
average)

thank you