I have a table with a date_created and date_expired and I want to look
at the 15th of each month and every month since the system started and
count up how many accounts were active at each of those points in
time.
Will have to assume that if there's an expiry date bigger than today
then that account was active at each of those points in time.

Can someone pelase tell me how can I do that?

Thanks a lot