> ## Documentation Index
> Fetch the complete documentation index at: https://docs.mixpanel.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Track User Retention
Our [Retention](/docs/reports/retention) report in Mixpanel is designed to help you assess user engagement over a specified period of time. Have you achieved product market fit? Are your users returning over time or churning? Which cohort of users come back and what drives them to?
To follow along the tutorials here, create a copy of [this board](https://mixpanel.com/project/3018488/view/3536632/app/boards/#id=6350511) from our demo project and copy into your own project. As you open the linked board, you will see instructions to click on "Use this board" to transfer it over to your project and to edit the default date range.
## Understanding Retention Criteria
Define retention analysis to calculate users who come back on a specific time unit (e.g. day, week, month) or any time unit afterwards. You can also switch the retention mode between the default rolling time window and calendar defined time window.
## Understanding Frequency Criteria
Define retention analysis to calculate users who did the event in at least X unique intervals or in exactly X unique intervals.