Daily retention is defined as the number of active devices on day X / total active devices during the entire retention period. ​

• Active devices on day X: The number of unique devices with at least one session on day X during the selected retention period.
• Active devices during the entire retention period: The total number of active devices where the user has at least one session throughout the entire retention period.

For example, if an app was first downloaded by 120 users on May 1st and after 90 days, 100 of those users opened the app at least once, their 100 devices become 100 active devices and the leftover 20 are taken out of the equation.

If 30 of these users' active devices log a session on May 8th (7 days after the initial download) then the retention will be 30% on day 7.

In this example, Day 0 = May 1st, Day 1 = May 2nd, Day 2 = May 3rd, Day 3 = May 4th, Day 7 = May 8th and so on.