Duolingo

Duolingo is the most successful language learning app in history, downloaded over 500 million times and used daily by more people than are learning foreign languages in the entire US school system combined. Its AI-driven approach has redefined what free language education looks like.

Adaptive AI Learning

Duolingo's algorithm, originally developed with researchers from Carnegie Mellon and Duolingo's own data science team, adapts the difficulty, pacing, and content mix for each individual learner. It identifies which skills each user has mastered, which are being forgotten (spaced repetition), and which need more practice — personalizing the learning path in real time.

Gamification Design

Duolingo pioneered language learning gamification: streaks (daily practice rewards), XP points, leaderboards, hearts (lives system), leagues (weekly competitive brackets), and achievement badges. The design makes practicing feel like a game — users often describe checking off their daily Duolingo as a habit they can't break even when they try.

Duolingo Max (AI Features)

Duolingo Max builds on Super Duolingo (the subscription tier renamed from "Duolingo Plus" in 2022) with two GPT-4-powered conversation features:

• Roleplay: Practice real-world conversations (ordering food, asking for directions) with an AI that responds and corrects in the target language
• Video Call: Live AI video conversations with a virtual character (Lily) for immersive speaking practice, with post-call feedback on accuracy and complexity

As of early 2026, Explain My Answer — the grammatical-explanation feature that originally launched as Max-exclusive — is free for all users. Max's differentiated value now sits almost entirely in Roleplay and Video Call.

40+ Languages

Duolingo teaches 40+ languages including Spanish, French, German, Japanese, Korean, Mandarin, Arabic, Hindi, and more. Less common courses include Irish, Hawaiian, Welsh, and Latin. Duolingo's AI team has pioneered methods for building language courses from limited training data.

Research-Based Curriculum

Duolingo's courses are built on linguistic research and validated by learning outcomes data. The platform published research showing that 34 hours of Duolingo Spanish is equivalent to a full college semester — backed by testing methodology.

Pricing

Free with ads (full app, no time limits). Super Duolingo (formerly Duolingo Plus): $12.99/month or $95.99/year (no ads, streak repair, unlimited hearts). Duolingo Max: $29.99/month or $167.99/year (Super features plus AI Roleplay and Video Call). Family plan: $119.99/year for up to 6 accounts.