How to Time Reactivation Campaigns for Maximum Impact — Jackson Shuttleworth, Duolingo

Each day a user skips the app they get a practice reminder push (Duolingo's most powerful notification), up to a series of 7. At 7 days of inactivity the practice reminders are turned off because the extra value from continuing is much lower. The key window is the first 3-4 days: for a daily-use app, users not back by then are very hard to win back.

Instead of asking users at onboarding when they want to be reminded (morning, evening, a set time), schedule the next day's practice reminder for 23.5 hours after the user's first practice of the current day, so it tracks when they actually practiced the day before. Tested against many other scheduling strategies; user-set times lose because people are rarely free at the same time forever.

For users lapsed from about 1 to a few weeks, send a weekly progress-report email comparing this week's activity to last week's (XP earned, time spent). Email gives more room than a push to users who may have uninstalled. Test many copy tones for the lapsed case: hopeful ('Have you taken a break? Come back and jump in'), a challenge ('seems like a slow week. How much are you going to learn this week?'), or slightly passive-aggressive. Showing simple engagement stats and letting the user infer the value was cheaper to build than content-specific recaps (words learned) and got most of the benefit.

Machine-learning-driven system chooses the notification copy (push and email) for each user and optimizes on its own; PMs just add copy variants to the pool (soon AI may write them). Never treat a notification as 'done': the practice reminder has been under continuous experimentation for 6 years. Judge variants on open and click-through rates, which reach significance fast at scale. Lapsed users deserve the most experimentation because you know least about what they need.

End-of-year recap in the style of Spotify Wrapped showing each user's learning stats. Even users who only used the app for a few days months earlier get a delightful, funny recap the moment they reopen. Outreach to long-lapsed users is tied to a moment and personal value rather than 'here's a product update'. Timed so returning users flow into New Year's resolution season.

Build reactivation campaigns around moments that match users' mental model of the product: back to school (people get into a learning mindset even if not in school) and the start of the year (learning a language is a common New Year's resolution). The end-of-year review brings users back just before resolution season. Guest values timing plus the right message over the specific creative.

Using the in-app social graph (55-60% of users have a friend), prompt active users to reach out to friends who have been gone for months ('get them to come back'). The message comes from a person, not the brand. Returning users are then eased into social features such as friend streaks (learning alongside that friend). Even winback messages from strangers met on the leaderboard get higher click-through than Duolingo's own messages.