Rolling count between dates?

[yvonne-c]

Can anyone help with counting the data in this table (sample attached)  into a table like the one below

ID	DateOn	DateOFF
A	29/10/2015
B	20/04/2018	20/04/2018
C	20/04/2018	20/04/2018
D	21/03/2013
J	28-01-2017	07-05-2018

All IDs have a 'dateon' which will be counted unless there is a 'dateoff'

So ID A will be counted within all months below as it has been present for all of these months

J would only be counted in Feb- Apr as it was not present after May

I just need the

Thanks!

	Total on
Feb 18	14
Mar 18	14
Apr 18	14
May 18	12
Jun 18	12
Jul 18	12
Aug 18	12
Sep 18	11