@Toby the OOTB component, by default includes all members, it would require customization to report Active members.
Reporting on "Active" members starts with defining what active means for your Community, active in the last 30, 60, 365 days? Are active members as defined, only those who login, those who post? How often do they need to post, to be considered active, once, once a month (Causal user vs Superuser)? Also consider users who do not post, if your community is public facing, then anyone who visits your community (observers) and finds information could be considered an "active user", private communities require login
Once you define that, there are several ways to slice n dice the metrics, check this post for details Community Analytics & Metrics Definitions about the different ways to report on Members. For example, Registered Members shows a breakdown of active community members over the last 60 days, Observers, Casual Members, Superusers.
When I was at Sprint I also used Signin & Registration metrics (can be found in Admin Metrics) to track activity for Members (logged in). We typically looked at "Active" within a month time frame, then averages it out over a year.
I know that is a long answer, but "Active" can mean different things for different Communities 😉
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