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Reviewed and published by trentmaziarz, March 21, 2026. Discovered and drafted by our automated research pipeline.
Duolingo uses an AI algorithm called Half-Life Regression to predict when a learner is about to forget a word or skill, then schedules a review exercise just before that happens. It works like a smart calendar for your memory — timing reminders to keep knowledge fresh without over-drilling what you already know. The system was published as a peer-reviewed research paper in 2016 and has been in production use since.
Details
Developed by Duolingo researcher Burr Settles and published at the Association for Computational Linguistics (ACL) conference in 2016, Half-Life Regression uses a mathematical model of memory decay (p = 2^(-Δ/h), where Δ is time since last practice and h is the estimated half-life of a memory) to predict recall probability for each word in a learner's vocabulary. It accounts for features like word frequency, morphological complexity, and whether a word is a cognate in the learner's native language. A/B testing showed a 9.5% increase in retention for practice sessions and a 12% increase in overall activity compared to the simpler Leitner card-sorting method it replaced. Duolingo open-sourced the algorithm and released a dataset of 13 million learning traces on Harvard Dataverse.
Products affected
Duolingo
Sources & Evidence
Company Disclosure
Other practices by Duolingo
Customer SvcDuolingo uses an AI chatbot (powered by a company called Decagon) to handle the majority of customer support requests for the Duolingo English Test. The AI fully resolves about 80% of chat inquiries without any human involvement, answering questions about test registration, scores, and institutional acceptance.Data AnalysisDuolingo uses a machine learning model to decide, in real time, whether to show each individual user an advertisement, a subscription offer, or neither — predicting which choice is most likely to generate revenue from that specific person at that moment. The system was credited with generating tens of millions of dollars in additional annual revenue.Data AnalysisDuolingo uses a machine learning algorithm to decide which push notification to send each user, at what time, and how often — optimizing for the messages most likely to get a lapsed learner back into the app. The system was published as research in 2020 and was shown to increase the number of daily active users by 0.5% and improve retention of new users by 2%.
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