In 2018, after years of explosive growth, Duolingo's Daily Active Users (DAUs) stagnated to single-digit YoY growth rates. What happened next is one of the most compelling case studies on how to align data, product, and marketing that’s publicly available. As proof, between 2018 and 2024 Duolingo grew their DAUs by 900% with growth rates higher in recent years than previous ones (a very rare feat).

To get there, Duolingo did 4 things arguably better than anyone else:

Let’s dig in and learn the language of growth!

… see what I did there?! Duolingo.. language…okay I’ll shut up.

When Duolingo began its journey to solve slowing growth, they did what most companies do. They jumped into experiments and product building. First, they tried gamification:

However, to speed up iterations they borrowed what other companies were doing and tried to apply it to Duolingo. The result? From the mouth of their CPO at the time “The first attempt to reignite growth through more gamification resulted in a dumpster fire.” The strategy and vision effectively imploded and was dismantled.

Then, they tried referrals. Referrals is always a go-to for companies because there's the assumption that because it works for other companies, it'll work for you.

Duolingo took inspiration from Uber and tried to install their own referral program. While more successful than gamification, it only moved moved new users by 3% and that couldn’t justify the effort they were putting into it.

What happened next, though, is a Masterclass in how to use data to rally an organization.

The team took a step back and modeled their growth to better understand:

This led to the introduction of Duolingo’s growth model:

The model above classifies users into 7 mutually-exclusive user states per day:

Note: This is very similar to what I recommend for how to properly calculate MAUs (although Duolingo focuses on DAUs).

They then created rates and ratios between these states to understand how users were flowing in and out of segments.

For example:

By calculating these rates and ratios they were able to build a projectable growth model because you could use the last time period to predict the next one.

T_-1 → T₀ → T₁

Knowing they could build a projectable growth model they could also build a sensitivity analysis to see which metric they needed to focus on to move the needle. Specifically, they wanted to know what would happen to DAUs if each rate (CURR, NURR, etc.) grew 2% MoM over 3 years:

Improving the current user retention rate (CURR) had by far the biggest impact, so that's what they doubled down on. They created a new team, the Retention Team, with CURR as its North Star metric and got to work.

With the new focus for the team, Duolingo started shipping some of the most beloved product features still used today: leaderboards and streaks. Now it’s easy to just write a simple sentence like that but there was a ton of experimentation and discovery and thought behind it that led to it.

Here’s a great podcast from the PM who leads the streak efforts on how they did it. Now, I’m not a product expert so I can’t speak much about it, but by all accounts, the product was starting to hum. However, what's more interesting to me as a Marketer are the Marketing changes that also started to drive impact.

And what they accomplished here is nothing short of world class.

Duolingo is legendary for its aggressive and witty push notifications but their journey to get here is super fascinating too. By 2018, they had been experimenting with push notifications for a while, but their efforts had faded. However, after the decision to improve CURR they refocused on it but with one condition (that came from the CEO).

One push notification per day per user.

Why? He had been warned by Groupon’s CEO about their cautionary tale. Groupon found early success with email and went all in eventually sending up to 5 emails a day. Over time, the impact of each email faded and they effectively destroyed the channel. People learned to ignore Groupon emails. So, to avoid the same thing happening at Duolingo, the rule was that users could only receive up to 1 push notification a day.

Then, like any good data driven company, they invested in data science and experimentation. They first ran a 30 day experiment where they sent all different types of notifications to different users at different times simply to collect data. They started analyzing all the data and began building a bandit algorithm to deliver these personal push notifications at scale.

However, one challenge with the bandit algorithm is that it will continue to “invest” in winning notifications faster than a standard A/B test. Duolingo clearly didn’t want repeat and spammy push notifications so they added another factor to the algorithm to suppress notifications that were sent too close together.

Essentially, the further in between 2 similar push notifications, the better the notification score. This introduced variety to the push notifications but also reduced fatigue. The impact was intense with the former CPO sharing that the efforts “generate dozens of small- and medium-size wins that have amounted to substantial gains in DAU year after year. “ From push notifications. Owl-shit crazy.

Finally, to fully understand how much Duolingo invested in the martech powering push, at one point they were able to send 6 million+ notifications within 5 seconds during the 2024 Superbowl. The crazy part? It was a tech ask from Marketing. That’s what happens when your leadership understands the power of Marketing.

But, beyond tech, they also invested in people which brings us to the last reason they’ve grown their DAUs by 900%.

By 2023, 80% of Duolingo users came in organically. I haven’t looked but I assume the LTV / CAC ratio is likely a 1 Billion : 1. How’d they achieve this? Well, currently, Duolingo has 16M TikTok, 4M Instagram, and 800K LinkedIn followers.

On TikTok, they are in a league of their own and that dominance started in 2020 when they hired Zaria Parvez straight out of college to own the channel. And by all accounts, she OWNED it taking the follower count from 50K to 16M before she left to now lead Social Media at DoorDash. By crafting a culturally relevant, unhinged, and unchecked persona, Zaria created a personality in Duo that is culturally unmatched. Everyone on social media knows the owl.

While it’s really hard to replicate this success, the part that I love and is often unspoken about is the culture at Duolingo that allowed her and her team to take off. Here are 2 examples.

Example 1: In an interview with ADWEEK, Zaria shared how just that morning she had put a mustache on the CEO to create a spoof of Apple’s Severance. “He was like, ‘I only have 30 minutes to do this because I have a meeting with our biggest investor,’ but he still prioritized it,” said Parvez.

The CEO didn’t say no. The CEO didn’t question it. The CEO made time. Let that sink in.

Example 2: The social media team had little red tape or approval required. This was the process that the social media team went through:

“Even if everyone internally is not happy, if it’s good for the brands and people think it’ll lead to impressions and lead to impact, then we move forward with it,” - Parvez

The executive team understood the job and got out of their way. This type of autonomous decision making at speed (because being culturally relevant requires speed) has led to some unbelievable campaigns. For example, just this past May, Duolingo took social media by storm by pronouncing that their owl had been killed.

One campaign alone shot up their Instagram followers by 25%!

I LOVE when organizational culture allows talent to excel.

Beyond just organic followers, Duolingo has cultivated partnerships with Netflix (Squid Games), Mattel, and so many other brands. I can’t go more than a few days without seeing or hearing something about Duolingo popping up. The beautiful part is it feels so natural (dare I say organic) and it’s a brilliant way to stay top of mind which feeds back to DAUs.

See Duo on Social → Remember you have a streak → Lesson → DAU

But, follower count is one thing. It’s another thing to have those followers be highly engaged. Just look at LinkedIn (where they have the least amount of followers and it’s the least “social”). They are likely getting hundreds of thousands (if not millions) of impressions here which again triggers Duolingo to be top of mind.

The beautiful thing about all of these are that they are each individually moats.

Duolingo’s approach to quantifying users and using a growth model is a moat.

Building product features that customers are obsessed with? Moat.

Push notification strategy that delivers impact? Moat.

Organic domination? Moat on top of another moat surrounded by a moat.

And that’s how Duolingo grew their DAUs by 900%

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