"I’ve never seen a growth story like this before—4.5x growth for a mature product, driven by a small handful of product changes, rooted in an innovative growth model, and explained in such actionable detail."

"By mid-2018, daily active users (DAU) were growing at a single-digit rate year-over-year, which was troubling, given the explosive growth the company had seen in the past. This was a problem for a startup with investors anxious to see fast monetization growth."

"We prioritized working on retention over new-user acquisition because all of our new-user acquisition was organic, and, at the time, we didn’t have an obvious lever to pull to supercharge that."

"First, Duolingo had already implemented several gamification mechanics successfully, such as the progression system on the home screen, streaks, and an achievements system."

"And second, top digital games at the time had much higher retention rates than our product, which I took as evidence that we hadn’t yet reached the ceiling for gamification’s impact."

"But there was one small issue: we had no idea which incremental gamification mechanics would work for Duolingo."

"A three-minute Duolingo lesson felt similar to a Gardenscapes match-3 level, and Duolingo and Gardenscapes both used progress bars to provide visual feedback on how close the user was to completing the session."

"The moves counter allowed users only a finite number of moves to complete a level, which added a sense of scarcity and urgency to the gameplay."

"We gave our users a finite number of chances to answer questions correctly before they had to start the lesson over."

"The reward was a free month of our premium subscription, Super Duolingo (at the time, it was called Duolingo Plus). Seemed like a pretty good offer to us!"

"Instead, new users increased by only 3%. It was positive, but not the type of breakthrough we needed."

"When you are playing Gardenscapes, each move feels like a strategic decision, because you have to outmaneuver dynamic obstacles to find a path to victory. But strategic decision-making isn’t required to complete a Duolingo lesson—you mostly either know the answer to a question or you don’t."

"However, our best and most active users already had Super Duolingo, and we couldn’t give them a free month when they were already in a plan. This meant that our strategy, which needed to rely on our best users, actually excluded them."

"In other words, we needed to use better judgment in adapting when adopting. Being more systematic in just this area would have made a big difference in what gamification mechanics we chose to pursue."

"Zynga separated their users and measured retention based on the following weekly retention metrics:"

"The blocks, or buckets, represent different user segments with different levels of engagement. And every single user who has ever used the product is in one, and only one, bucket on any given day."

"At-risk WAU: inactive today, but active in at least one of the prior 6 days  At-risk WAU + DAU = WAU"

"The fact that DAU, WAU, and MAU can easily be calculated from these buckets made it easy to model them over time."

"Additionally, by manipulating the rates represented by the arrows, we can model the compounding and cumulative impact of moving these rates over time; in other words, the rates are the levers product teams can pull to grow DAU."

"With the model created, we started taking daily snapshots of data to create a history of how all of these user buckets and retention rates had evolved on a day-by-day basis over the past several years."

"With this data, we could create a forward-looking model and then perform a sensitivity analysis to predict which levers would have the biggest impact on DAU growth."

"In hindsight, the CURR finding made sense, because the Current User bucket has an interesting characteristic: current users who stay active return to the same bucket."

"This produces a compounding effect, which means that CURR is much harder to move, but when it does, it will have a greater impact. Based on this analysis, we knew that CURR was the metric we had to move in order to get that strategic breakthrough we wanted"

"One of the biggest benefits of focusing on CURR was deciding not to work on things that seemed paramount before, especially new-user retention."

"This was a huge mindset shift for a company that had tremendous success spending years running the bulk of its growth experiments on new users first."

"Another big lesson was seeing the massive gap between how a metric could impact DAU vs. MAU; for example, CURR’s impact on DAU was 6 times its impact on MAU."

"I still thought gamification was a good place to start when trying to improve retention."

"After some consideration, we decided to bet on leaderboards."

"I had hypothesized based on my personal experience as a player that the closeness of the competitor’s engagement would be more important than the closeness of personal relationships."

"I thought this would be especially true in a mature product where many users’ friends weren’t active anymore."

"Leagues provided users with a greater sense of progress and reward, an integral element in game design."

"They also increased engagement over time, since engaged users move up to more competitive leagues week after week."

"We deliberately made our leaderboard as casual and frictionless as possible; users were automatically opted in and could progress to the top of the first league by merely engaging consistently in their regular language study."

"Going forward, the leaderboards feature became a vector for improving metrics, and teams continue to optimize the feature to this day. Also importantly, the leaderboard was the Retention Team’s first breakthrough!"

"Based on substantial A/B testing in prior years, Duolingo had established that notifications can be a big vector for growth, but that impact had plateaued for us over the years."

"As we started diving into this, there was one principle that became paramount. It came from a cautionary tale from Groupon’s CEO. He explained to Luis von Ahn, our CEO, that for a long time, Groupon stuck to one email notification per day."

"The CEO eventually gave in and allowed his team to test sending one more email to each user each day. This test resulted in a big increase to their target metrics."

"Encouraged, Groupon kept experimenting, sending more emails, even as many as five a day."

"Then, in what felt like a change from one day to the next, their email channel lost most of its effectiveness. Over time, the accumulation of Groupon’s aggressive email tests had basically destroyed their channel."

"He discovered that if a user reached a 10-day streak, their chances of dropping off were reduced substantially."

"But it turns out that there is a surprisingly large number of optimization opportunities around streaks."

"We got our first big win with the streak-saver notification—a notification that alerts users with streaks if they are about to lose their streak."

"After this, several improvements followed: calendar views, animations, changes to streak freezes, and streak rewards, among others. Each helped improve upon the original streak idea and generated substantial improvements to retention."

"I recently met one user who told me, “I have a 1,435-day streak!” and added, “with no streak freezes!” His bragging rights were well-earned, as he had been studying his chosen language daily for almost four years."

"One of those is that a streak increases user motivation over time; the longer the streak is, the greater the impetus to keep the streak going."

"Each day that a learner comes to Duolingo, they care a bit more about coming back the next day than they did the day before, hence increasing retention and DAU."

"Luckily, several of these bets worked, including expanding internationally, building social features (this is what the Acquisition eventually team pivoted to, with great success), accelerating course content creation, working with influencers, increasing our presence in schools, investing (a little bit) in paid UA, and going crazy viral on TikTok."

"Last year was one of the fastest growth rates in Duolingo’s history. The quality of the user base also improved; the share of our DAU with a streak of 7 days or longer increased almost 3 times to more than half of our DAU."