Since ROWS(B1:B20) is always 20, why not:
SUM(--(FREQUENCY(IF(C1:C20="Jul",MATCH(B1:B20,B1:B20,0)) ,ROW(1:20))0))

"Bob Phillips" wrote in message
...
Try this array formula

=SUM(--(FREQUENCY(IF(C1:C20="Jul",MATCH(B1:B20,B1:B20,0)) ,ROW(INDIRECT("1:"&ROWS(B1:B20))))0))

--

HTH

Bob

"Cassie" wrote in message
...
I needed to count all the unique names by month. Names in Col B and the
months are in col c. the names appear multiple times in the file
at least once in each month - I only want to count John Smith once in
January
but his name appears 4 times in January

Thanks
Cassie