Duolingo's most powerful re-engagement notification is one sent after five days of inactivity stating, "these reminders don't seem to be working. We're going to stop sending them." This passive-aggressive message makes users feel the app is "giving up on them," which is surprisingly effective at getting them to return.

Counterintuitively, providing new, varied bonuses frequently can keep customers engaged longer than a single, large permanent upgrade. This is because customers quickly get used to permanent features, while novelty continually recaptures their interest.

A key viability metric for consumer subscription apps is achieving 30-40% Day 1 retention. Anything lower suggests a fundamental product-value mismatch, making it mathematically difficult to acquire enough users to build a sustainable active user base.

After reaching scale, a product's dormant user base is a massive growth opportunity. Activating these users requires designing specific return experiences, like Duolingo’s proficiency tests, which can be a bigger lever than new user acquisition.

To solve low adoption for its government services app, Irembo targeted a niche audience (car owners) with a high-frequency need (checking for traffic fines). This recurring use case provided a compelling reason for users to download and retain the app, creating opportunities to expose them to less frequent services.

A review widget that performs well on desktop by being large and comprehensive can be distracting and hurt conversions on mobile. On smaller screens, a more subtle, less intrusive social proof element is often more effective as it doesn't detract from the primary call-to-action.

Instead of optimizing for retention metrics, April's founders set an extremely high bar for their own use. By ensuring the product was reliable enough for their own critical tasks, like sending investor emails, they naturally built a product with strong user retention.

Move beyond simple product usage for retention. Design a clear "adoption ladder" with defined milestones that encourages customers to deepen their relationship with your brand—progressing from user, to community participant, to podcast guest, and even to business partner. This creates immense stickiness and fosters evangelism.