DATEDIFF returns wrong value

Hi,

I have a simple statement below, which I expect to return values quarterly.  But with the given dates below it returns 1 and I expect 0 because there is no quarter passed between them.  Can anyone suggest what's wrong with this:

DECLARE @startDate AS DATE = '20090518'
DECLARE @endDate AS DATE = '20090701'

SELECT DATEDIFF(quarter, @startDate, @endDate)

I am using British format, but that shouldn't affect as the above date declaration should handle that correctly.

Thanks