Duolingo

Description

Luis von Ahn grew up in Guatemala City observing a distinct divide. Families with money sent their children to English language private schools. Everybody else had no realistic route to learning the language that controlled access to higher education, professional opportunities, and international communication. Von Ahn went to one of those private schools himself, moved to the United States to attend university, studied computer science at Carnegie Mellon and graduated with a PhD, sold his own security technology company reCAPTCHA to Google in 2009, and then turned his full attention to the question he had carried around since he was a child: why does quality language education still cost money most of the world doesn’t have?

He found his co-founder at Carnegie Mellon. Severin Hacker, a Swiss computer scientist who was doing graduate work at the university, had also been working on a prototype for sharing written content via mobile phones on his own. When von Ahn saw what Hacker was working on in 2009, he flew to meet him in Vancouver two days later. Duolingo originated from that meeting. The private beta launched in November 2011 and drew more than 300,000 people to a waiting list before the product opened to the general public on June 19, 2012 – by which time the waiting list had reached 500,000. Von Ahn and Hacker had created something that people wanted badly enough to wait for.

Duolingo is a language learning application that teaches reading, listening, speaking, and writing with short exercises in a game-like structure every day. As of 2025, the platform has over 575 million registered users and over 40 different language courses. The app is available on iOS, Android and web browsers and is free to download and use in its basic form. Duolingo went public on the Nasdaq in July 2021 and has grown to be a company valued at about $9 billion.

HISTORY

The original business model for Duolingo was to fund free education through translation work. Users would learn a language by translating real documents — web articles, legal text, business communications — and the platform would sell those translations to companies. The model was a borrowing from von Ahn’s earlier thinking about reCAPTCHA, where humans solved problems that computers could not while creating value for somebody else. By learning Spanish, for example, a user would also be helping to translate a news article from Spanish to English and Duolingo would collect payment for that service.

The translation business eventually gave way to a freemium advertising model and then, progressively, to subscriptions. Duolingo Super is the premium level that removes advertisements, lets you make unlimited mistakes without losing your progress, and enables you to access offline lessons. The core curriculum has always been free, a non-negotiable principle for von Ahn based on the founding mission.

Union Square Ventures led the first institutional funding round for Duolingo in 2011 with $3.3 million. Subsequent rounds ensued: $15 million from New Enterprise Associates in 2012, and rounds that totaled $108.3 million by 2017 at a $700 million valuation. Duolingo passed the $1.5 billion valuation mark in December 2019. The Covid-19 pandemic led to a massive growth as schools were closed and self-directed learning increased. The company filed for its first public offering in 2021 and went public at a valuation that reflected its status as the world’s most downloaded education app.

The platform went beyond European and Latin American languages over time. Duolingo added Japanese, Chinese, Korean, Arabic, and Hindi. It also brought in the use of constructed languages such as High Valyrian from the HBO series Game of Thrones and Klingon from the Star Trek series, which got a lot of attention and proved that language learning could be used by people who are not interested in practical communication. The Duolingo English Test, which was introduced as an alternative to traditional tests for English language proficiency, costs $49 and can be taken in 45 minutes from home, whereas tests such as TOEFL cost around $250 and require flying to certified testing centres. More than 3,000 institutions around the world — including Duke, the University of California, Los Angeles, Columbia, Dartmouth and Yale — accepted the Duolingo test as part of their admissions process as of 2021.

In February 2025, Duolingo’s marketing team staged a stunt in which the app’s owl mascot Duo appeared to die, with a notification telling users he had died waiting for them to complete their lessons. The campaign created a massive media hit and proved the brand’s willingness to use the reputation of its mascot for aggressive reminders as an ongoing creative tool.

Lesson Structure

Each lesson lasts for a few minutes and is made up of several types of exercises: the translation of sentences from and into the target language, the ordering of words in the correct order, the matching of vocabulary to images, listening to audio and transcribing what was said, and speaking into the microphone for pronunciation evaluation. The app blends these formats in one lesson to make the lesson varied. Units group lessons into a structured curriculum, and units group into sections that cover more complex grammar, vocabulary and sentence structure.

Streak System

The streak represents the number of days a user has been completing at least one lesson. The number is prominently displayed on the home screen and its primary retention mechanic. Losing a streak resets the counter to zero. Duolingo sells Streak Shields as an item that you can purchase with in-app currency, that protects the streak through one missed day. The streak mechanic is responsible for the daily notification behavior that the Duo owl mascot represents — the reminders come at user-set times and increase in frequency and urgency if ignored.

Leagues and Social Features

Users compete weekly against each other in leagues organized by experience points gained during the week. The best-performing teams in each league move up to a better league, while the worst-performing teams move down to a worse league, the following week. Leagues range from Bronze to Diamond with a leaderboard displaying each participant’s standing in real time. The system creates direct competition between strangers using the same app which boosts engagement significantly for users that are motivated by competition. Friends can follow each other, compare streaks and appear on each other’s friend leaderboards.

Hearts and Lives

The free tier restricts the number of mistakes a user could make in a session using a heart system. Every incorrect answer costs one heart; when all the hearts are gone the session is over. Hearts regenerate over time or can be filled up instantly with in-app currency. The system promotes careful reading and listening instead of careless guessing. Duolingo Super eliminates heart limits completely and lets you make as many mistakes as you want without interruption.

Speaking and Pronunciation Practice

The app uses speech recognition to assess user pronunciation. The speaking exercises require users to repeat phrases or to answer questions aloud. The recognition system determines whether the responses are correct or incorrect based on whether the audio spoken is the same as the expected output. Speaking exercises can be disabled in settings for those who practice in environments where speaking aloud is not practical.

Stories and Audio Lessons

Stories introduce brief narrative sequences with audio and dialogue, challenging the comprehension of the story with interactive choices within the story. Audio Lessons, available in certain courses, enable users to practice during commutes or other times when it is inappropriate to look at a screen. Both formats go beyond the basic translation and vocabulary practice.

Duolingo for Schools

A separate teacher-facing version lets educators assign lessons, track student progress, set goals and track completion rates across a classroom. The feature links student accounts with a classroom dashboard that is available to the teacher. Duolingo for Schools is also free and Educators have adopted the feature in formal classroom settings as well as supplemental homework assignments.

Duolingo ABC

A separate app for early literacy, Duolingo ABC teaches children to read using letter recognition, phonics and simple word exercises designed as short games. The app is aimed at children who are learning to read for the first time and is built on the same gamified progression model as the main language app.

CONCLUSION

Duolingo is working in a space where many attempted and failed to make a sustainable business. Rosetta Stone charged hundreds of dollars and developed a retail presence. Dozens of language-learning startups launched app-based courses and folded when they were unable to retain paying users long enough to recoup acquisition costs.

Von Ahn and Hacker bet that making the core product completely free — and then building addictive social mechanics around a learning curriculum — would generate enough scale to make a business work, through advertising and optional subscriptions. More than a decade, 575 million registered users and a public company valuation in the billions, the bet held. The owl is still sending the reminders, and most of the people who see them open the app anyway.