Try this...

Sheet1:

A2:A20 = dates
B2:B20 = numbers to sum

Sheet2:

A2:A13 = month names as TEXT entries in the form mmm: Jan, Feb, Mar, Apr,
etc.
B1:C1 = year numbers = 2009, 2010

Enter this formula in B2 Sheet2:

=SUMPRODUCT(--(TEXT(Sheet1!$A$2:$A$20,"yyyymmm")=B$1&$A2),Sheet1 !$B$2:$B$20)

Copy across to C2 then down to B13:C13

--
Biff
Microsoft Excel MVP


"Paul" wrote in message
...
I have a list of data by date of power production. What I want to know is
how much power was generated in December 2009, January 2010, etc. The data
in
a sheet with the dates in column A and power production in column B. I
have
another tab with the months in the rows and the years on the columns.

I am sure there is a way to do this with sumproduct, but i am not sure how
to.

Thanks in advance.