I have a pivot table whereby in column B I have a list of dates denoting when
the customer joined and in columns C-I I am showing the total business by
month, i.e:

Customer Ref Live Date Sept-07 Oct-07 Nov-07 (thru to Mar-08)
B01234 01/10/2007 £6834 £5702 £12614 . . .
B01111 01/09/2007 £4132 £7968 £18098 . . .

I'd like to show a running total amount of business placed by each customer,
but I'd like the total to refer only to those dates = the given live date,
and up to 12 months after the given live date.
Therefore for customer B01234, I only need to total the figures for Oct-07
and Nov-07, whereas for customer B01111, I need to total the figures for
Sept-07, Oct-07 and Nov-07.

I was thinking that perhaps this might be achieved by the 'calculated
field/item' pivot table function?

Any help would be gratefully appreciated.

Thanks