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Duolingo logo, featuring the mascot Duo
Available in
Headquarters Pittsburgh, US
Area served World
European Union (restricted)[1]
Founder(s) Luis von Ahn, Severin Hacker
CEO Luis von Ahn
Industry Online education, Professional certification, Translation, Crowdsourcing
Services Language courses, Duolingo Test Center, Duolingo for Schools
Employees 60[2]
Slogan(s) Free language education for the world
Website www.duolingo.com
Alexa rank Increase 760 (April 2017)[3]
Advertising yes
Registration yes
Users 150 million[2]
Launched 30 November 2011; 5 years ago (2011-11-30)
Current status Online
Native client(s) on Android, iOS, Windows Phone, Windows 10 Mobile
Written in Scala[4]
Presentation at Wikimania about Duolingo

Duolingo (/ˌdjˈlɪŋɡ/ DEW-oh-LING-goh) is a freemium language-learning platform that includes a language-learning website and app, as well as a digital language proficiency assessment exam. Duolingo offers all its language courses free of charge. As of November 2016, the language-learning website and app offer 68 different language courses across 23 languages, with 22 additional courses in development. The app is available on iOS, Android and Windows 8 and 10 platforms with about 150 million registered users across the world.[2][5][6][7]


The project was started at the end of 2009 in Pittsburgh by Carnegie Mellon University professor Luis von Ahn (creator of reCAPTCHA) and his graduate student Severin Hacker, and then developed along with Antonio Navas, Vicki Cheung, Marcel Uekermann, Brendan Meeder, Hector Villafuerte, and Jose Fuentes.[8][9]

Inspiration for Duolingo came from two places. Luis Von Ahn wanted to create another program that served two purposes in one, what he calls a "twofer".[10] Duolingo does this by teaching its users a foreign language while having them translate simple phrases in documents.

Forbes' staff member Parmy Olson revealed the other incentive towards creating Duolingo. Von Ahn was born in Guatemala and saw how expensive it was for people in his community to learn English. Severin Hacker (born in Zug, Switzerland), co-founder of Duolingo, and Von Ahn believe that “free education will really change the world”[11] and wanted to supply the people an outlet to do so.

The project was originally sponsored by Luis von Ahn's MacArthur fellowship and a National Science Foundation grant.[12][13] Additional funding was later received in the form of investments from Union Square Ventures and actor Ashton Kutcher's firm, A-Grade Investments.[14][15]

Duolingo started its private beta on November 30, 2011, and accumulated a waiting list of more than 300,000 users.[16] On June 19, 2012, Duolingo launched for the general public. Due to popular interest, Duolingo has received many investments including a $20 million Series C round of investment led by Kleiner Caufield & Byers and a $45 million Series D round of investment led by Google Capital.[17] Duolingo has 60 staff members, of whom many were Google employees,[18] and operates from an office in the Pittsburgh neighborhood of East Liberty.[19][20][21]

On November 13, 2012, Duolingo released their iOS app through the iTunes App Store.[22] The application is a free download and is compatible with most iPhone, iPod and iPad devices.[23] On May 29, 2013, Duolingo released their Android app, which was downloaded about a million times in the first three weeks and quickly became the #1 education app in the Google Play store.[24] Duolingo then released both a Google Glass App (glassware) and support for Android Wear.[25]

Business model[edit]

Core services of the platform are available for free. Duolingo uses only very limited advertising in both its Android and iPhone apps. There are no subscription fees for the tutorials. However, there were instances when the platform has been used for paid translation purposes.[26] In July 2014, Duolingo started a language certification service, Test Center, as a new business model. In June 2015, a Duolingo spokesperson confirmed that the company has been backing away from the translation business and in the future will instead focus on language certification and other (not yet announced) business opportunities.[27] According to Luis von Ahn, in order to offset the over $40,000 a day cost of developer salaries, server costs, etc., Duolingo now charges a fee to repair a lost streak or offers a paid streak freeze feature, at the request of users.[28] In April 2017, Duolingo began offering an optional paid subscription for US$9.99 per month which removes ads and allows lessons to be downloaded for offline use.[29]

Crowdsourced translation[edit]

To earn money, Duolingo originally employed a crowd sourced business model, where members of the public were invited to translate content and vote on translations. The content came from organizations that pay Duolingo to translate it. Documents could be added to Duolingo for translation with an upload account which had to be applied for.[30] On October 14, 2013, Duolingo announced it had entered into agreements with CNN and BuzzFeed to translate articles for the companies' international sites.[31]


As of 2015, the company has been valued at USD $470 million with a total funding of USD $83.3 million.[32] Venture capitalists, private investors and other investor firms that hold a stake in Duolingo include Fred Wilson,[33] Union Square Ventures,[34] New Enterprise Associates,[35] Ashton Kutcher,[14][15] Kleiner Perkins Caufield & Byers, Google Capital,[34] and Tim Ferriss.[36]


Language courses[edit]

Duolingo provides written lessons and dictation, with speaking practice for more advanced users. It has a gamified skill tree that users can progress through[22] and a vocabulary section where learned words can be practiced.

Users gain "experience points" (XP) as they learn a language, such as when they complete a lesson.[37] Skills are considered "learned" when users complete all the lessons associated with the skill. Users win one point for each correct answer, and lose one for each error, and validate the lesson when they reach 10 points. In an earlier version, users would start with four "lives" on early lessons[37] and three on later lessons, a "life" being lost with each mistake.

Duolingo also includes a timed practice feature, where users are given 30 seconds and twenty questions and awarded a skill point and seven or ten additional seconds (time depends on the length of the question) for each correct answer.[38] This timed practice feature is only available after purchase in the Lingot store for ten lingots, the currency the site uses. As the goal of Duolingo is to get people to learn the language, each skill (containing between 1 and 10 lessons) has a "strength bar" that corresponds to the computer's estimate of how strongly certain words or constructions still exist in the user's memory. After a certain duration of time, strength bars fade, indicating a need for a user to refresh/re-study that lesson, or to "strengthen weak skills." Courses can teach upwards of 2,000 words.[39] Duolingo uses a data-driven approach to lesson planning.[40] At each step along the way, the system measures which questions the users struggle with and what sorts of mistakes they make.

For each language, Duolingo also has a "Progress Quiz" feature, an extended quiz found in the Lingot store for 25 lingots. It measures the user's language learning progress on a 5 point scale, with 5 being the best score. This quiz is not adjusted to the player's level and only tests overall language competence.

The efficacy of Duolingo's Spanish course has been reviewed by a study commissioned by the company. Conducted by professors at City University of New York and the University of South Carolina, the study estimated that 34 hours on Duolingo may yield reading and writing ability of a US first-year beginners' course university semester, which takes in the order of over 130 hours. The research did not measure speaking ability. It found that a majority of students dropped out after less than 2 hours of study.[41] The same study found that Rosetta Stone users took between 55 and 60 hours to learn a similar amount.[42]


The lingot (a portmanteau of the words lingo and ingot, and also the French word for ingot) is the currency of Duolingo.[43] Users gain lingots by leveling up, finishing a skill, maintaining a usage-streak for a total of seven days, inviting others to Duo via social media, and by uploading documents to the Immersion. Items available in the lingot store include power-ups, practice and bonus skills. Users of the mobile apps can also customize the appearance of the Duolingo mascot, which is by default the green owl.[43] This feature is not available on the browser version. A hidden bonus skill included in some courses is "Christmas", which is only available in the period surrounding Christmas. Other Bonus Skills include "Flirting" and "Idioms and Proverbs".

In Spring 2017, a new currency called "gems" replaced lingots for some users on the iOS app, but not users on other app versions or the website.[44]

Language incubator[edit]

Instead of slowly adding additional languages, CEO Luis von Ahn announced on May 29, 2013, that they would create the tools necessary for the community to build new language courses, with the hope to introduce more languages and "empower other experts and people passionate about a specific language to lead the way".[45] The result was The Language Incubator,[46] which was released on October 9, 2013.[47][48] In addition to helping the community create courses for widely spoken languages, the Duolingo Incubator also aims to help preserve some of the less popular languages such as Latin, Mayan and Basque.[49] The first course entirely created by the Duolingo community through the Incubator was learning English from Russian, which launched in beta on December 19, 2013.[50] Other courses created by the Duolingo community include English from Turkish, Dutch and Hungarian, as well as French and Brazilian Portuguese from Spanish.

The Incubator has three phases. First, when sufficient interest to contribute to a new course has been received from volunteers fluent in both languages (a requirement for application), the course begins in "Phase 1: Not Yet Released". The second phase, "Phase 2: Released in Beta," begins when the course has been fully prepared and is ready for open beta testing. Finally, "Phase 3: Graduated from Beta" is when a course is considered relatively stable. The reason complete courses remain in the Incubator is that moderators/contributors can continue to improve the course. For example, if a student gets a question wrong but notices there was an error on the program's part that either misled the student or counted a correct answer wrong, then they may submit a report detailing what happened.

Courses for users who know English[edit]

As of 24 May 2017, 23 courses were available to the public from English (ordered by number of learners):

Nine courses for English speakers are currently in development (ordered by progression percentage towards completion):[51][52][53]

Courses not available in English[edit]

Catalan and Guarani are available as a second language for Spanish speakers. They are the only languages offered on Duolingo that are not available to English speakers.

Most other languages only offer a course into English. As of June 2, 2016, languages offering additional courses (some still in development) are Spanish (with courses into French, Portuguese, Italian, German, and Esperanto, as well as the Catalan and Guarani courses), German (into French and Spanish), Arabic (into French, German, Swedish, and Spanish), Portuguese (into Spanish, French, German, and Italian), Turkish (into German, Russian, and French), French (into Spanish, Italian, German, and Portuguese), Italian (into French, German, and Spanish), Chinese (into Spanish and French) and Russian (into German, French, Spanish, and Swedish).

Duolingo English Test[edit]

Duolingo launched Duolingo Test Center on July 22, 2014, now known simply as the Duolingo English Test. It is an online language certification platform that can be taken on the Web, iOS or Android, where tests are proctored through microphone and camera. There are two types of tests: Quick Test and Duolingo English Test (DET). Quick Test lets the user try some questions from the Duolingo English Test. The Duolingo English Test proper takes 40 minutes to finish, costs $49 USD, and is graded within 48 hours on a scale of 0 to 10.[58] Duolingo English Test allows just Google Chrome browser. According to a study conducted by University of Pittsburgh, there is a substantial correlation between the scores on Duolingo Test Center and TOEFL iBT.[59][60]

Upwork has adapted the DET score as one of their official qualifications with which freelance workers can prove their English fluency.[61][62] Duolingo is also collaborating with LinkedIn to allow the score to be easily incorporated into a user's résumé page.[58] Duolingo is working with twelve US universities, including Carnegie Mellon University, to study if the score can be reliably used as one of their admission qualifications.[63][64] More than 60 higher education institutions are now using the DET as an alternative or supplement to traditional exams.[65]

Duolingo for Schools[edit]

Duolingo has been used in schools. For example, in Costa Rica and Guatemala, Duolingo has been used in public schools as a pilot project run by the government.[66]

In January 2015, Duolingo released Duolingo for Schools, to provide teachers with a centralized dashboard that can display their students’ progress.[36] The dashboard helps teachers understand each individual student's weaknesses and strengths at each skill, and helps them optimize their language-teaching methods.[67]


Tinycards is a flashcards application made by Duolingo, wherein people can make and share flashcard sets.[68] After select users were invited to a closed beta test, Duolingo released the app for iOS devices on July 19, 2016 and for desktop on March 2, 2017.[69] Users can sign in with their Duolingo account and immediately choose which sets they are interested in. Some include "US Capitals" or "Human Skeleton Body." Additionally, sets from a user's language course taken on Duolingo will be available for flashcard review. Currently progress on Tinycards does not synchronize with progress on Duolingo.


Duolingo uses many services in the Amazon Web Services suite of products, including Amazon DynamoDB, Amazon Virtual Private Cloud, nearly 200 virtual instances in Amazon Elastic Compute Cloud (EC2), Amazon Simple Storage Service (S3) and Amazon Relational Database Service (RDS).[70] The server backend was originally written in the programming language Python,[71] but was rewritten in Scala by 2017,[4] the frontend in Backbone.js and Mustache. Duolingo provides a single-page web application for desktop computer users and also smart phone applications on Android (both Google Play Store and Amazon Appstore), iOS (App Store) and Windows Phone platforms. 20% of traffic comes from desktop users and 80% from mobile app users.[70]

Recognition and awards[edit]

In 2013, Apple chose Duolingo as its iPhone App of the Year, the first time this honor had been awarded to an educational application.[72] Also, Duolingo won Best Education Startup at the 2014 Crunchies,[19] and was the most downloaded app in the Education category in Google Play in 2013 and 2014.[73] In 2015, Duolingo was announced the 2015 award winner in Play & Learning category by Design to Improve Life.[74]

See also[edit]


  1. ^ Users of the EU cannot be involved in the translation of any documents: "Terms and Conditions of Service". Duolingo. Temporary Restrictions on Users from the European Union. Users within the European Union are not presently allowed to submit materials for translation or translated materials to Duolingo. While these users can continue to use the educational services offered through the Website, they will not be involved in the translation of any documents. If you submit a request for translation or translated materials to Duolingo, you thereby warrant and represent that you are not currently within the European Union, did not translate the document within the European Union, and will not be within the European Union when your translation request has been finalized. 
  2. ^ a b c "Duolingo moving to East Liberty, plans to add employees". The Business Journals. Retrieved March 24, 2016. 
  3. ^ "Duolingo". Ranking. Alexa Internet. Retrieved April 23, 2017. 
  4. ^ a b Rewriting Duolingo's engine in Scala
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  6. ^ "Duolingo – Learn Languages for Free". Windows phone. Microsoft. Retrieved November 21, 2014. 
  7. ^ Guliani, Parul. "Duolingo Looks To Dominate The Mobile Education Market With New Flashcard App TinyCards". Forbes. Retrieved 2017-02-17. 
  8. ^ Siegler, MG (April 12, 2011). "Meet Duolingo, Google's Next Acquisition Target; Learn A Language, Help The Web". TechCrunch. Retrieved November 21, 2014. 
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  10. ^ Mayer-Schönberger, Viktor; Cukier, Kenneth (2014). Learning with Big Data: The Future of Education. Houghton Mifflin Harcourt. pp. 9–10. ISBN 978-0-54435550-7. 
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  68. ^ "Tinycards - Flashcards by Duolingo". tinycards.duolingo.com. Retrieved July 27, 2016. 
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  70. ^ a b "AWS Case Study: Duolingo". Web Services. Amazon. Retrieved March 28, 2015. 
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External links[edit]