Seems to work. Nice one!

--
Biff
Microsoft Excel MVP


"Lori Miller" wrote in message
...
I couldn't come up with a single formula

i haven't time to test it thoroughly but maybe with a similar setup...
try this in E2 with CTRL+SHIFT+ENTER and fill down:

=COUNT(1/(A$2:A$12="AC")/(FREQUENCY(IF(A$2:A$12="BD",
-ROW(A$2:A$12)),IF(A$2:A$12<"BD",-ROW(A$2:A$12),0))=D2))