How it works
Take a cohort of users who installed on the same day, which counts as day 0. Day-N retention is the number of them who opened the app on day N, divided by the size of the cohort. This is classic retention. Rolling retention counts users who came back on day N or on any later day, and so is always higher. Range retention counts anyone active within a period, for example days 7 to 13. The figure also depends on what counts as a return: any app open, or a specific event such as placing an order.
Why it matters for an app team
Retention is the clearest early signal of whether users find the app worth keeping, and it drives lifetime value directly: revenue per user can only accumulate while the user is still around. Compared across campaigns, it separates sources that bring lasting users from those that bring one-time installs.
In practice
Example with made-up numbers: 1,000 users install on a Monday. 380 open the app on Tuesday, 150 on the following Monday and 70 thirty days after install. Day-1 retention is 38%, day-7 is 15% and day-30 is 7%.
Common confusion
Two tools can show different retention for the same app because they use different definitions: classic or rolling, calendar days or 24-hour periods counted from the install time, different time zones. Fix the definition before comparing numbers or setting targets. Retention is also not the opposite of the uninstall rate, since many users who stop coming back never delete the app.