Sum of year dependant on start month

Hi All,

I have a problem with a formula and don't know where to start. I have a spreadsheet with 12 months of data for 2012 for many differennt Orgs.

I need to be able to sum up the total for an "Org" for 2012 but dependant on when the agreement starts.

e.g.

If an agreement starts OCT 2011 and lasts for 12 months in would only need to get the total for that ORG for the period JAN 2012 - OCT 2012 as I only need the amounts impacting 2012.

I have attached a spreadsheet which hopefully wxplains better.

As always many thanks in advance for anyone who can help