How Our Viral Growth Metrics Align with Andrew Chen’s Theories

When a product goes viral, it feels like magic—millions of impressions, skyrocketing sign-ups, and that exhilarating sense of momentum. But as Andrew Chen points out in this article (https://andrewchen.substack.com/p/my-product-went-viral-on-social-media), virality alone doesn’t build long-term success. Retention does.

At Lettre, we’ve been analyzing our D1, D7, D30, and D36 retention metrics, and what we found strongly supports Andrew Chen’s framework on growth loops, engagement, and the importance of compounding retention effects.

Let’s break it down.

Retention: The Real Measure of Product Stickiness

In his article, My Product Went Viral on Social Media – What Happened Next?, Andrew Chen highlights a crucial truth:

📌 “Going viral is great, but if you don’t retain users, the growth is meaningless.”

📌 “Retention is the foundation of sustainable growth—without it, acquisition is just a leaky bucket.”

We couldn’t agree more. Our own retention data illustrates exactly how a viral product can maintain and even amplify its growth when retention loops kick in.

Setting the Benchmark: What Good Retention Looks Like

Before diving into our numbers, let’s define retention in simple terms:

• D1 Retention: The percentage of users who return the day after their first experience.

• D7 Retention: The percentage who are still engaged a week later.

• D30 Retention: The percentage who stick around after a month.

• D36 Retention: An additional long-term marker to track engagement beyond the first month.

The typical benchmark for a strong consumer product:

✔️ D1: 60%

✔️ D7: 30%

✔️ D30: 15%

Our Actual Retention Numbers: A Case Study in Sustained Growth

Here’s what we observed in our latest cohort analysis:

✔️ D1: 92% – Our users are immediately hooked!

✔️ D7: 70% – We maintain a strong connection with our audience.

✔️ D30: 30% – We’ve doubled the industry benchmark, proving lasting engagement.

✔️ D36: 48% – A fascinating retention spike!

These numbers reinforce Andrew Chen’s argument that successful viral products don’t just acquire users—they create systems that bring them back.

The Mystery of Day 36 📈: Growth Loops in Action

One of the most interesting insights? A retention spike at D36. Normally, retention declines over time, but something happened around Day 36 that re-engaged a large number of users. (We think it was the release of the PenPals feature as it was released around that time)

Andrew Chen describes this as the power of growth loops—self-sustaining systems where user engagement drives more engagement. Potential explanations for our D36 spike:

🔹 A re-engagement trigger – Perhaps an automated email, notification, or social reminder prompted users to return.

🔹 Network-driven interactions – Users might have seen friends engaging again, sparking renewed interest.

🔹 A latent activation loop – Some users may have taken longer to hit their "aha moment," but once they did, they stuck around.

This aligns perfectly with Chen’s “growth loops” framework, where retained users act as a catalyst for further retention—compounding engagement over time.

What This Means for Viral Growth

Andrew Chen explains that virality without retention is an illusion—a spike followed by a crash. Our data proves that sustained engagement is what turns virality into real, long-term success.

💡 Virality is a growth hack. Retention is a business strategy.

💡 Compounding retention loops create network effects that drive sustainable growth.

💡 A well-designed engagement strategy ensures that new users don’t just visit once—they stay.

What’s Next? Optimizing for Even Higher Retention

With these insights, here’s how we’ll improve retention even further:

✅ Reverse-engineering D36 – We’ll dig deeper into what caused that spike and see if we can trigger it earlier. As of now, we think it’s the release of the PenPals feature

✅ Strengthening growth loops – We’ll optimize referral, social triggers, and re-engagement mechanics.

✅ Expanding long-term retention – We’ll focus on increasing D30-to-D60 retention through personalized experiences.

What does this mean?

• Last 12 months: Over the past 12 months, we’ve closely monitored user retention trends to understand how well our product is engaging and retaining users over time. By analyzing cohort data, we can identify key moments when engagement has improved, plateaued, or declined, helping us refine our strategies to maximize long-term user retention.

• Importance of a flattening curve: Ideally, a healthy product should exhibit a retention curve that stabilizes rather than continuously declining. A flattening retention curve means that a core group of users continues to engage with the platform consistently over time, demonstrating strong product-market fit and long-term stickiness. In our case, we observe that retention begins to stabilize around Week 33, indicating that we’ve successfully built a habit-forming experience for a significant portion of users.

• Impact of PenPals: A key inflection point in our retention trend aligns with the launch of PenPals in September 2024. This feature was designed to enhance user interaction, deepen engagement, and provide ongoing value beyond the initial onboarding experience. The fact that retention began to flatten right after its release strongly suggests that PenPals played a critical role in increasing user stickiness. This correlation validates our hypothesis that social and community-driven features significantly contribute to long-term retention.

• This is what really keeps us going and why it matters: Seeing a flattening retention curve post-Week 33 is a major milestone—it signals that we are building a sustainable, engaging product that keeps users coming back. This is what motivates us to keep iterating and optimizing the experience. Moving forward, our focus will be on doubling down on social engagement, refining the PenPals experience, and exploring additional features that encourage long-term user connections.

Final Thoughts

If your product is built for virality, take Andrew Chen’s advice: don’t just chase new users—focus on keeping them.

Retention isn’t just about engagement metrics; it’s about building a habit, creating a community, and designing growth loops that sustain themselves.

Our numbers prove that when you build something sticky, users don’t just visit—they return, engage, and grow the product alongside you.

Would love to hear from other product teams—have you ever seen a late-stage retention spike like our D36? What worked for you? Drop your insights in the comments! 🚀