Good, free, fun: The simple formula that has made Duolingo a daily habit for millions

Perhaps no app has mastered user loyalty quite like Duolingo, the gamified language-learning platform 34 million people a day can't put down. Here, CEO and co-founder Luis von Ahn tells the BBC why their insistent owl works so well.

The day I started working on this story about Duolingo it seemed to be everywhere. I heard from a friend who was celebrating her 800-day Spanish practice streak on the app. I read about a journalist from The Guardian who became addicted to learning Italian. A Sri Lankan waitress in Brooklyn switched from English to Spanish when she heard my mother and I speaking, crediting Duolingo for her skills.

But my deep interest in the world's most downloaded language-learning app truly began last year when I saw first-hand its significant impact on new migrants to the US, a country undergoing one of the largest migration waves of the decade. At some point in their long journeys, Duolingo becomes an essential tool for these people on the move.

John Jairo Ocampo, a former bus driver from Colombia, recalls struggling to find work in his first days in the US in 2023, when a boss at a construction site in New York City explained simply, "More English, more money." He used Duolingo to learn. Now, the family lives in Indianapolis, and John’s wife is using the app to get along better at her job in an elementary school kitchen; she says her boss is using it, too, to learn Spanish.

The migrant experience is not foreign to Duolingo's CEO and co-founder, Luis von Ahn, who was born and raised in Guatemala, a Central American country with over 55% of its population living in poverty.

"In a Latin American country, and in Guatemala in particular, if you have money, you can buy a very good education, but if you don't have money, sometimes you don't even learn how to read and write," Von Ahn told the BBC in a recent interview at Duolingo's brand new office in downtown New York. "That made a big impression on me."

So when non-native English speakers Von Ahn and Severin Hacker, Duolingo's CTO and co-founder, started their company in 2012, they knew that learning languages, and in particular learning English, has the potential to change people's lives. "This is why we've worked really hard to keep Duolingo free, because we want to give access to education to everybody."

To maintain the promise of an open and free app, Von Ahn and Hacker developed a hybrid business model that combines ad-supported access and "freemium" elements, while also offering a paid subscription with extra benefits, like an ad-free experience and a family plan. And it worked. "The main way in which we grow is by word of mouth, so people tell their friends," he says. One such word of mouth moment came from Bill Gates, who said in a Reddit chat back in 2015 that he regretted not speaking more languages and had tried Duolingo.

In the intervening years the app has found its way onto many, many screens. According to Duolingo's shareholders letter, in 2023 the company's revenue was $531m and the forecast for the full-year 2024 is $731m. Roughly 8% of Duolingo users pay for a subscription, contributing to 80% of the company’s revenue. Meanwhile, the vast majority, 90%, use the free version and see ads, which account for only 8% of the earnings.

The app combines short, engaging lessons and game-like elements to help users develop speaking, reading, writing and listening skills in 41 languages. Around half of users are practicing English, and Duolingo can be used to learn other major world languages like Spanish and Chinese, as well as some lesser-spoken languages, such as Esperanto, Navajo and even High Valyrian, a fictional language developed for HBO's Game of Thrones. There was some controversy last year when Duolingo paused its Welsh language course. The app now offers maths and music courses, as well.

To keep people coming back daily, Duolingo created a streak system and fashioned characters with strong personalities, such as the infamous green owl, Duo, and a goth purple-haired teen, Lilly. These characters send daily practice reminders and, based on social media posts, are magnetic to users.

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The brand has taken advantage of Duo's popularity as evidenced by its TikTok videos, where it does "very strange stuff", as Von Ahn described. "At first it was just this owl, then I think it started getting a life of its own when the notifications from the phone started coming from the owl. People started ascribing it a personality, and then I think people started memes for the owl, because the owl is very insistent," he added. Still, he sees the appeal.

"I cannot speak French to another person, but I can speak French to her," Von Ahn says of Lilly, opening his phone to demonstrate Duolingo's new product released at Duocon this summer, which allows conversational practice. The CEO, who claims he is shy when speaking new languages, talks enthusiastically with the app in good French with a bumpy accent (he says he spends 30 minutes a day in the app and is also learning Swedish and Japanese). "Most people are like me," he says, explaining why this is his favourite feature. "When they're not very good at a language, they just don't want to speak to another person. So it's going to let people actually practice."

Today, Duolingo serves 34 million daily users worldwide and employs 850 people across six cities: Detroit, Seattle, Berlin, Beijing, New York, and their headquarters in Pittsburgh, where you can discover the company's culinary spin-off, Duo's Taqueria. This global presence affirms the company's accelerated growth. In October 2024, Duolingo's market capitalisation was $12.27bn, a significant rise from 2022, when its market cap was $2.85bn.

The CEO's journey to becoming a tech-founder billionaire began when he was an eight-year-old boy in Guatemala City, where his single mother, a doctor, gifted him a computer instead of the Nintendo he had wanted. He left Guatemala in 1996 to study mathematics at Duke University. He went on to pursue a PhD in computer science, and it was during his first year at Carnegie Mellon University, in 2000, when a pivotal moment occurred.

The young doctoral student attended a talk in which Yahoo!'s head scientist shared 10 problems the company couldn't solve. "At the time [Yahoo!] was the biggest internet company, it was huge. Yahoo! gave free email accounts to people, and there were malicious people that were writing programs to obtain millions of email accounts, and they didn't know how to stop them. I went home, I thought about it, and came up – along with my PhD advisor – with the idea of a Captcha, that is the distorted characters that people have to see online [to prove that you’re a human]," he reveals.

Captcha, an acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart", served as the foundation for ReCaptcha – best known today as Google's I am not a robot verification system. It was not only a technological improvement, but also a company founded and solely owned by Von Ahn. In 2009, Google acquired it for an undisclosed eight-figure sum, along with a game that helped improve the accuracy of Google Image Search. By his early-30s, von Ahn had become a millionaire.

Although Luis von Ahn didn't become the mathematics teacher he dreamt of being as a teenager in Guatemala City, these milestones, and the awards he has won along the way, allowed him to create an educational platform that now lives in the pockets of millions worldwide. Here, he tells the BBC more about his un-put-downable app and how a self-proclaimed "people-pleaser" gets by in the C-suite.

What do you think sets Duolingo apart from its competitors?

Duolingo's free version is really good, and I think that matters. And the second one is that we early on understood that the hardest thing about learning something by yourself is staying motivated, so we have spent a lot of time making Duolingo fun. With Duolingo it feels like you're playing a game as opposed to education apps which are just trying to teach you something without engaging you.

How does Duolingo keep users engaged and coming back?

Gamification is probably the most important thing. We try to turn the whole thing into a game, but we try to use storytelling. From the beginning, I wanted to have a mascot. I thought that it would make the whole thing more accessible. And having it doing weird things online really helps. But it's not like it started in one day. This is an evolution. It all works together to create a brand that people love. Most of the [features] we have now, we got to by trial and error. We've tried too many things that didn't work. The ones that are now there is because we tried them, and they did work.

How do you create habituation?

It really depends. People who are learning English, which are half of the users, generally actually want to learn English. They really care. The others, it's more of a hobby. If you take a user in the US and you ask them, "why are you using Duolingo?" Very common answers [are]:"I used to play a lot of Candy Crush" or "I used to look at a lot of Instagram and now I'm doing Duolingo instead, and at least I'm learning a little bit of Spanish or a little bit of German or whatever". So it's kind of like a productive use of time.

Even when apps and screen time can be seen as problematic, is your hope is that Duolingo is creating a positive habit?

We want it to be positive. When we decided to start teaching maths and music, these are two things that we thought are just positive. We may expand to other subjects, but we're going to try to continue doing things that are positive.

We're unlikely to [teach] the Pokemon characters, for example. Maybe people want to learn that, but we just want to do things that are good for the world, and we want parents to feel good about giving their kids this app. We want it to be the case that after you use the app, you feel like you did something good.

Duolingo's website claims to have a diverse workforce from more than 30 countries, why is that important for a platform like yours?

We have a lot of international employees and that's been really good. Sometimes you don't know what's going on in a certain country, and then an employee from the country tells us: "the reason this is not working is because you translated that word wrong".

Do you see strange sentences often? Can you share an example?

Most of our sentences are useful sentences, like "where is the bathroom", but some of them are just strange, and that has helped our virality.

One that always stuck with me, I think it was in the Danish course. The sentence said: "Over there, behind the bed, lies the body of her husband". And it's like, what is that? What is that sentence?

What is the most challenging part of being a CEO of a large company?

I don't think we're very large, we are 850 people. Two things for me. When we were smaller, when we were like 50 people, everybody trusted me because they spent time with me directly, and they're like "OK, he's a nice guy". Once I have more than, I don't know, 300 people, I can't spend time with everybody. And so, it’s much harder for trust to happen. And a lot of times I have to make decisions that are not popular.

When you are very close to somebody else and they make an unpopular decision, you understand them because you're like, "OK, ultimately I know they are a good person". And the other one that's been hard, but this is a very personal thing, I'm very conflict avoidant and sometimes I have to tell people something they don't like. And that's hard for me.

Is it hard for you to tell people something that will hurt them?

I am a people pleaser and it's good and bad. I married a Swedish woman and, let me tell you, she's direct. In our culture, in Latin America, you're so indirect. In Guatemala we just go around the subject and around the subject, to try to make them understand, but never tell them. Whereas Swedish people are just like: "I don't like you". And it's just like, "wait, why are you saying that?" We would never say that in Latin American culture.

It must be difficult for you to fire someone.

Oh, my God! Yes! It's horrible.

The first person I fired, when we were a very small company, it was a woman. I fired her at the end of the day one day. And then the next day I came into the office, and she was still here. And it turned out she didn't understand that I had fired her because I never said "you're fired". I just went around it, and I thought she understood. And then we hugged, and I thought that was the end of it. Then I came in and I'm like "Why are you here?" She said "we had a really good conversation yesterday; I will do a better job". And I'm like "No". And then I had to fire her again.

I've learned that the wrong way to fire somebody is to build up to it. You [have to] start by saying "I am so sorry. I'm going to have to let you go". You say it first, so that it's super clear.

Where are you looking to grow; are you focused on particular emerging markets or new demographics?

Markets matter. Right now, we have users in every country in the world. The ones that are our big focus are the US, UK, Germany, France, Japan, China, Brazil, Spanish-speaking Latin America, India, Italy and Turkey. I may have missed one, but these are the countries where we have people on the ground and where we're spending.

Do you think that an app like Duolingo could be becoming an alternative method for education or other skills more broadly?

Yeah, I think you can learn other skills, but I don't think that an app will replace schools or universities. That's because schools and universities serve other purposes. Schools, for example, serve the purpose of childcare. And universities, you get to learn how to be an adult. But I do think you'll be able to learn almost everything in an app.

Also, from a global standpoint, [many] people don't have access to a good teacher or a good education. So hopefully they'll be able to learn with this.

Do you see Duolingo occupying that space?

I would like that. I don't know if we'll be able to teach everything, but I would like that.

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