in b2 in "Analysis":

=SUMPRODUCT((Sheet1!$A$2:$A$4=$A2)*(MONTH(Sheet1!$ B$1:$D$1)=MONTH(TODAY())-3)*(Sheet1!$B$2:$D$4))

in C2:

=SUMPRODUCT((Sheet1!$A$2:$A$4=$A2)*(MONTH(Sheet1!$ B$1:$D$1)=MONTH(TODAY())-2)*(Sheet1!$B$2:$D$4))

Copy both down

Sheet1 is you "Data Source"

HTH

"DoooWhat" wrote:

I am quite certain that SUMPRODUCT is the solution to my problem, but
I cannot get it to work correctly. My 'Data Source' sheet looks like
this:

A B C D
1 Account No. 5/2007 6/2007 7/2007
2 001 100.00 200.00 300.00
3 002 50.00 60.00 70.00
4 003 10.00 11.00 12.00

The sheet ('Analysis') that I am performing my analysis on will look
like this:

A B C
1 Account No. Last 3 Months Last 2 Months.......
2 001 600.00 500.00
3 002 180.00 130.00
4 003 33.00 23.00

For the purpose of my question, let's focus on getting the formula for
cell B2 on the 'Analysis' sheet. I suspect the formula will work like
this:

=SUMPRODUCT((condition that matches account number on Analysis to Data
Source)*(condition that selects which months to include)*(some range
of cells))

Any help would be very much appreciated.

Kevin