=SUMPRODUCT(--(A1:A100<>""),--(B1:B100<>""),(B1:B100-A1:A100))/SUMPRODUCT(--
(A1:A100<>""),--(B1:B100<>""))

--
HTH

Bob Phillips

"Krishna Mohan" <KrishnaMohan@discussions.microsoft.com> wrote in message
news:511F2E1C-D1FC-465A-800E-83EDD502039C@microsoft.com...
> Hi,
> I have a situation like this below..
> 18-Feb-02 02-Jun-04
> 26-Jul-02 08-Jun-04
> 29-Jul-03 10-Jun-04
> 22-Oct-03 05-Jun-04
> 01-Nov-03 10-Jun-04
> 11-Nov-03 14-Jun-04
> 18-Nov-03 04-Jun-04
> 20-Dec-03 21-May-04
> 30-Mar-04 10-Jun-04
> 08-May-04 22-Jun-04
> 29-May-04 15-Aug-04
>
>
> 11-Jun-04 11-Jul-04
> 12-Jun-04 16-Jun-04
> 22-Jun-04 28-Jun-04
> 24-Jun-04 26-Jun-04
>
> 10-Dec-04 23-Dec-04
>
>
>
> 28-Aug-04 01-Sep-04
> 28-Sep-04 29-Sep-04
> 08-Dec-04 22-Dec-04
>
> 20-Aug-04 29-Aug-04
>
> 25-Aug-04 31-Aug-04
> 30-Aug-04 10-Sep-04
> 03-Jan-05 10-Jan-05
> 27-Sep-04 05-Oct-04
> 30-Sep-04 07-Oct-04
> 03-Oct-04 04-Oct-04
>
> The above are two columns of excel. I want to calculate the average of the
> difference for each month in another work sheet like bwlow
>
> Month Difference..
>
> Can some one help me on how I can do that