Retention
On this page
Definition
Retention is the share of users who return after their first action, over a given period. Classic retention counts those returning strictly on a specific day, rolling retention within a window, and unbounded retention on any day after start. The meaning of the metric depends entirely on how “returned” is defined and which window is used.
How to compute
Group users into cohorts by start day and, for each period, compute the share still active: . Assemble the result into a cohort matrix whose columns are periods since start. State the activity definition separately: opening the app, a key action, or a payment.
Pitfalls
Without an explicit activity definition retention is meaningless: the same number yields different metrics at different thresholds. The first period is the noisiest. Compare cohorts over the same window length. Calendar events and seasonality distort cohort-to-cohort comparisons.