How this language learning app got 300 million users without spending a dollar on marketing

How did Duolingo get up to 300 million users within three years of launching? What’s the secret to keeping so many users engaged?

“How many of you have had to fill out a web form after being asked to read a distorted sequence of characters like this? … How many of you found it really, really annoying? … I invented that!”

Luis von Ahn, inventor of captchas and computer science professor at Carnegie Mellon University, always gets a laugh with those lines at the start of his talks, and so he did at the Surge conference in Bangalore last week.

But the captchas – which confirm users are humans and not robots – are only an ice-breaker for talking about his current passion. Luis is the co-founder and CEO of Duolingo, a free language learning app with 300 million users worldwide. It’s the most downloaded app in the education category on both Google Play Store and iTunes.

The world’s richest man, Bill Gates, was a Duolingo user, albeit briefly.

Duolingo uses a task-based, gamified, multiple choice format to get you up to speed on using a language. If you’re an English speaker, you can choose from 16 other European languages to learn currently – that is, Spanish, French, German, etc. For a Hindi speaker from India, it uses Hindi to teach English. At a very basic level, that involves asking questions in Hindi and getting the user to pick the right translation in English by looking at pictures, as you can see in this screenshot.

It gets more interesting as you progress in the course. Machine learning at the back-end automatically adjusts the difficulty level depending on your performance in the lessons which range from listening and speaking to multiple choice tests. A study claims 34 hours spent on Duolingo by the average user is equivalent to a university semester of language education.

Although Duolingo does not yet teach Asian languages to English speakers, it teaches English to speakers of Hindi, Mandarin, Japanese, and most Asian languages. The priorities are based on demand and RoI (return on investment) – Spanish, for example, is the most popular choice for English-speakers wanting to learn a foreign language.

How to keep users engaged

The world’s richest man, Bill Gates, was a Duolingo user, albeit briefly. He confessed on a Reddit AMA that he “feels stupid” for being monolingual, and envies Mark Zuckerberg for being able to talk to the Chinese in Mandarin.

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Luis claims the effectiveness of these methods accounts for the popularity of Duolingo. “We didn’t spend a single dollar on marketing,” he says. Awareness spread by word of mouth, such as that of Bill Gates, even though he later dropped off.

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See: 10 top-funded edtech startups bucking the trend in India