Calculate if user is active

I'm trying to get a monthly overview of users enrolled. As of now I can only see the current number of active users, but would like to go back in time, and see how many enrolled users we had each month. The data (in danish) looks like this:

The highlighted coloum represents a boolean value to check if the user is active. This is basically done by evaluating the "afgangsdato" coloumn which states the day the user got inactive. How can i get the number of active users for each month?