How would you measure user engagement for a mobile app — what metrics would you use and how would you structure them?
Engagement is multi-dimensional: breadth (how many users engage), depth (how much they do per session), and frequency (how often they return). A robust engagement framework stacks these three layers into a metric hierarchy and links them to retention curves, because engagement that does not predict long-term retention is usually noise.
How to think about it
Three-layer engagement hierarchy
Layer 1 — Breadth (who engages)
- DAU / MAU ratio: measures what fraction of the monthly user base engages daily. A ratio above 0.20 is considered strong for most consumer apps; Slack and WhatsApp exceed 0.50 for their core user base.
- Active user definition: be explicit. An “active” user opened the app? Completed a core action? The denominator must be pinned before comparing periods.
Layer 2 — Depth (how much per session)
- Actions per session: for a news app, articles read; for a social app, posts liked or comments written.
- Session depth percentage: % of sessions reaching a “meaningful” milestone (e.g., reading more than one article).
- Content completion rate: videos watched to 75 % of duration; tracks played to end.
Layer 3 — Frequency (how often they return)
- D1, D7, D30 retention curves: the canonical way to visualise frequency.
- L7 / L28 (days active in last 7 / 28 days): a distribution, not a scalar, which shows user stickiness spread.
- Churn rate: % of users who were active last month but inactive this month.
Linking engagement to outcomes
Engagement metrics are only useful if they correlate with business outcomes. Run a cohort analysis: do users who score high on depth in week 1 show higher D30 retention? Do high-frequency users convert to paid plans at higher rates? If not, the metric may be a vanity measure.
Worked example — Duolingo. Breadth: DAU/MAU = 0.55 (exceptionally high). Depth: streaks completed per DAU, lessons finished per session. Frequency: D7 retention = 38 %. Correlation check: users who complete a 7-day streak in week 1 show 2.1x higher 90-day retention — this validates streak completion as a core engagement metric worth optimising.