Spaced Repetition: The science behind effective review
Why do we forget most things within 24 hours — and how can interval learning change that? A look into cognitive psychology.
Hermann Ebbinghaus discovered the forgetting curve in 1885: without review, we forget up to 70% of what we learned within 24 hours. That sounds depressing — but it is actually good news. Because the solution has been known for over 100 years.
The forgetting curve and what helps against it
Ebbinghaus also showed: every time we review something just before forgetting it, the curve flattens. The material stays longer. And longer. Eventually it is permanently stored.
Spaced Repetition leverages exactly this principle. Instead of reading the same material five times in a row, you review it at growing intervals: today, tomorrow, in 3 days, in a week, in a month.
How the algorithm works
Modern spaced repetition systems (the most well-known algorithm is SM-2, developed by Piotr Woźniak) evaluate after each review how well you remembered. Flashcards you know well are shown less frequently. Difficult cards come back sooner.
The result: you spend your study time exactly where it matters most — on the things you almost, but not quite, know.
Why traditional flashcards are not the same
Physical flashcard boxes without an algorithm can approximate spaced repetition — but you have to manage yourself when each card comes up. In practice, this fails due to discipline and time constraints.
Digital tools with a built-in algorithm take over this management for you. You open the app, study the cards that are due today — done.
In practice: What you should do differently
15 minutes daily beats 2 hours before the exam
This sounds trivial but is scientifically proven. Distribute your study time over weeks, not over one night. Your long-term memory will notice the difference.
Your own cards > other people's cards
Creating flashcards is itself a learning method. When you reformulate material into a question and answer, you process it more deeply. AI-generated cards from your own material are a good compromise: topic-specific and quickly created.
Conclusion
Spaced Repetition is not a new invention — but AI finally makes it scalable. What used to be manual work can now happen automatically. The principle remains the same as in 1885. The implementation is 2026.