Graph of System Usage

I have a table of users of a system.  Each row contains details of the user account, including the date that each user account was created and, if they have left the business, the date it was deactivated.

How can I create a graph which shows, for each month the system has been live, the number of total live user accounts?

If possible, I'd like to do this using Excel and Pivot Tables / Charts (but could use PowerBI if needed).

Thanks in advance