Reports - active people every month

[mrafs]

I'm trying to figure how to do a report.....that lists how many people are active each month.

names.fp7

event name.fp7

event line.fp7

The event line has a date as well as a status field (on waiting list / active / de-activated).

I know how to create a report listing activity broken down into months totaling how many people changed each status each month but not a running total of how many people active in each month.

ideas please....