Spaced repetition
Spaced repetition is a learning technique that schedules review of new information at increasing intervals — minutes, hours, days, weeks — to fight the forgetting curve.
The forgetting curve, mapped by Hermann Ebbinghaus in 1885, shows that memory of newly learned information drops sharply within 24 hours unless it is reviewed. Spaced repetition deliberately re-exposes the learner to the material at intervals tuned to that decay rate. Each successful recall pushes the next review further out — minutes become hours, days, weeks, months.
Modern spaced-repetition algorithms (SM-2, FSRS, Anki) decide the interval per card based on how easily the learner recalls it. Cards you struggle with come back in minutes. Cards you nail are scheduled three months out and survive for years on a few minutes a week of total study.
Spaced repetition is best suited to discrete factual knowledge — vocabulary, definitions, quotes, theorem statements, key dates. It is not a substitute for the deep reading and synthesis that build genuine understanding, but it stops what you understood from leaking out of memory.
Summio’s Practice mode generates spaced-repetition flashcards from the summaries you saved. Cards inherit the source’s structure — quotes, key definitions, glossary terms — so review re-exposes you to the exact passages that mattered when you first read.
Read more about Summio →Common questions
Does spaced repetition really work?
Yes — it is one of the most consistently replicated findings in cognitive science. Reviewing material at increasing intervals dramatically improves long-term retention compared with massed (cramming) study.
How long do spaced repetition reviews take per day?
For a steady-state deck of a few hundred cards, 5–15 minutes a day is typical. The algorithm spreads load across days; once you stop adding new cards the daily review burden drops.
Is spaced repetition only for language learning?
No — that is its most popular use, but the technique works for any discrete factual content: medical terminology, legal cases, history dates, software shortcuts, formulas. It is less useful for skills that require integrated practice (writing, coding, music).