with year in C1 i.e. 2005:

=SUMPRODUCT(--(MONTH(A1:A5)>3),--(YEAR(A1:A5)=C1),(B1:B5))+SUMPRODUCT(--(MONTH(A1:A5)=3),--(YEAR(A1:A5)=C1+1),(B1:B5))

HTH

"Bumblebee" wrote:

> I have a quarterly time series and I always want to sum the last three
> quartes of a year and the first of the next year and I can't think of a
> simple way to do it.
> e.g.
> A B
> 31/3/2005 1000
> 30/6/2005 3500
> 30/9/2005 6790
> 31/12/2005 8000
> 31/3/2006 9000
>
> So I would want to add quarters 6, 9 and 12 of 2005 and 3 of 2006 in this
> case but in general quarters 6, 9, 12 of year xxxx and 3 of year xxxx+1