The science is not in question.

Spaced repetition — the practice of reviewing material at increasing intervals, just before you would have forgotten it — is one of the most thoroughly researched techniques in cognitive science. The evidence that it works for vocabulary retention is overwhelming, consistent, and has been replicated across decades and dozens of studies.

The question is not whether to use spaced repetition. The question is which tool to use it with.

And this, in 2026, is a much more interesting question than it used to be.

A Very Quick Primer on How It Works

Spaced repetition is based on the forgetting curve — the observation that memory decays over time in a predictable pattern. If you review a word once, you will remember it strongly immediately after, but that memory fades. If you review it again just before it fades, the memory is strengthened and lasts longer. Review it again at the right moment, and it lasts longer still.

Do this enough times, with the right spacing, and a word moves from short-term recall into long-term memory. The word becomes something you know, not something you are studying.

The scheduling of these reviews — when to show each word, how long to wait between repetitions — is what separates a good spaced repetition app from a bad one.

The Options in 2026

Anki — The original. Still the benchmark.

Anki has been the gold standard for spaced repetition since 2006. Its SM-2 algorithm (and its modern successors) schedules reviews with a precision that has never been beaten by the consumer apps. The community has produced millions of decks covering every subject imaginable. The desktop app is free.

The trade-off is well known: Anki requires significant manual effort. You build your own decks, or you find decks and edit them. The interface is functional in the way that a 1998 spreadsheet is functional. Setup takes hours. Maintenance is ongoing.

If you are the kind of person who enjoys optimising systems and does not mind the overhead, Anki is extraordinarily powerful. If you want something that works immediately without configuration, it is the wrong choice.

Best for: dedicated, technically inclined learners who want maximum control.

Vokabulo — The AI-native approach

Vokabulo was built on the same core insight as Anki — that spaced repetition is the most effective way to make vocabulary permanent — but it solves the problem Anki leaves open: where does the vocabulary come from, and how does it arrive in context?

In Anki, you are responsible for the content. You source the vocabulary, write the sentences, find the audio, format the cards. In Vokabulo, the AI handles all of this. You capture a word from wherever you encountered it, and the system generates a complete, context-rich card immediately.

The spaced repetition algorithm in Vokabulo adapts to your individual performance — not just in the aggregate, but at the word level. It tracks which specific words you keep getting wrong, which you are confident about, and which you have not seen for long enough, and schedules reviews accordingly.

What separates Vokabulo further is the starting point. Anki's retention system is powerful, but the vocabulary it retains is whatever vocabulary you put in. Vokabulo's vocabulary comes from your actual life — the words you encountered because you needed them, in the contexts where you encountered them. This is not a small difference. Context is the primary determinant of whether vocabulary sticks in long-term memory.

Best for: learners who want powerful retention without the manual overhead, especially those learning from real-life situations.

Duolingo / Duolingo Max — Spaced repetition as a feature, not a core

Duolingo uses a form of spaced repetition to cycle through its vocabulary, but the algorithm is significantly simplified compared to Anki or Vokabulo. The primary design goal is keeping you engaged and returning daily, which means the scheduling is partly driven by gamification logic rather than pure memory optimisation.

For beginners, this is fine. The vocabulary is simple enough that imprecise scheduling still works. At the intermediate and advanced level, where you have hundreds of words in your active study set, the difference between a good algorithm and a mediocre one becomes much more noticeable.

Best for: beginners who want a gentle introduction to spaced practice.

Quizlet — Flashcards with limited SRS

Quizlet has a "Long Term Learning" feature that incorporates spaced repetition, but it is not the core of the product. Quizlet is primarily a flashcard tool — the spaced repetition is an add-on rather than a fundamental design principle.

Best for: students with a specific, short-term memorisation goal.

What to Look for in a Spaced Repetition Vocabulary App

Beyond the algorithm itself, there are three questions worth asking:

Where does the vocabulary come from? This is often overlooked, but it is critical. The best spaced repetition algorithm in the world cannot help you retain vocabulary that arrived without context. Words learned in context are remembered far better than words learned as isolated pairs.

Does it adapt to you individually? Generic scheduling — review everything every three days — is better than nothing but significantly weaker than an algorithm that tracks your specific performance on each word and adjusts accordingly.

Does it fit your real life? A system you use consistently is worth more than a theoretically perfect system you abandon because it is too complicated. The best spaced repetition app is the one you actually open every day.

The Conclusion

Anki remains the most powerful spaced repetition system available for learners willing to invest in setup and maintenance.

For everyone else — and particularly for learners whose vocabulary comes from real-life situations rather than textbooks — Vokabulo offers the same retention science in a form that works immediately, generates context automatically, and builds vocabulary from the situations you are actually in.

The science has been settled for decades. The question now is just how little friction you want between you and the benefits.

Experience spaced repetition without the setup overhead. Download Vokabulo and let the AI handle the cards while you handle the learning.