How it works
Each successful recall pushes the next review further out; a failed recall resets the interval and starts it over.
What spaced repetition is
Spaced repetition is a review schedule based on the forgetting curve: memory decays predictably over time, and reviewing an item right before you would have forgotten it resets the decay and lengthens the interval before the next review is needed. Cramming reviews too early wastes time on things you already remember; reviewing too late means you have already forgotten and have to relearn from scratch.
Why it beats fixed review schedules
A textbook that reviews chapter one vocabulary once, in chapter five, treats every word identically regardless of how well you actually know it. A spaced repetition system tracks each item individually — a word you find easy might not resurface for months, while one you keep missing comes back the next day. This individualized scheduling is why apps built around it, like Anki, are dramatically more time-efficient for long-term retention than blanket review.
How it shows up in language apps
Anki is the purest implementation: an open algorithm, user-built decks, and full control over scheduling. Memrise builds spaced repetition into its core vocabulary courses, resurfacing words at increasing intervals as you demonstrate recall. Duolingo uses a lighter version internally to decide which old material to slip back into new lessons, though it exposes less control to the user than a dedicated tool.
Getting the most out of it
Spaced repetition is only as good as what you feed it. Cards built from words you actually encountered in context — a show you watched, a conversation you had — stick far better than a generic frequency list, because you already have a memory hook attached. Reviewing daily matters more than reviewing for long stretches occasionally, since missed reviews compound and create a backlog that is discouraging to face.
Frequently asked questions
How long should I spend on spaced repetition daily?
Ten to twenty minutes is enough for most learners once a deck is established; the efficiency comes from consistency, not duration.
Should I make my own flashcards or use a shared deck?
Shared decks (common for exam prep, like JLPT vocabulary lists) save setup time. Self-made cards from real context you have encountered tend to be remembered better.
Does spaced repetition work for grammar, not just vocabulary?
It works best for discrete facts like vocabulary and verb forms. Grammar patterns and sentence production benefit more from a structured course and real practice.
