What you're describing is Recurring Retention (also called "compounded" retention), which measures whether users return in each successive time window — not just relative to a fixed "Day 0" birth event.
In Mixpanel, this is controlled by the retention type:
Birth retention (retention_type=birth) — the default — measures how users return relative to when they first did the "A event" (Day 0 / Week 0).
Recurring/Compounded retention (retention_type=compounded) — measures whether users who were active in one time window return in the next time window, i.e., week-over-week retention.
In the UI
When building a Retention report, you can switch between these two types. The compounded type will show you, for each week, what percentage of users who were active that week also came back the following week.
Via the API
You can query this using the retention_type=compounded parameter:
GET /retention?retention_type=compounded&unit=week&interval=1&interval_count=8
[Retention API]
Additional tip: Calendar vs. Rolling mode
If you want the weekly buckets to align to calendar weeks (e.g., Mon–Sun) rather than rolling 7-day windows from each user's birth event, you can switch to Calendar Retention Mode in the advanced settings under Retention Criteria. This ensures all users entering within the same calendar week are grouped together. [Calendar Retention Mode]
