Count occurances between dates

I'm sorry as I know others have asked similar questions, but how do you count the number of certain criteria between dates?
I need to count the number of "completed" for each month.

Column A Column B
12/07/2019 On order
18/07/2019 completed
03/08/2019 On order
04/09/2019 On order
26/09/2016 Completed
28/09/2016 Completed

The results I need to see are:
July = 1
August = 0
September = 2

Thanks in advance

Thanks Olly, that will do nicely!