Spaced Repetition: The Scientific Method to Remember Anything Long-Term
You read a fascinating article. Three days later, someone asks you what you remember from it. You stammer. A week later, you're not even sure you read it. Welcome to the forgetting curve, the best-documented mental trap in the history of cognitive science. And good news: there's a way out. It's called spaced repetition, it's 140 years old, and it's the foundation of every modern memorization tool.
1885: Hermann Ebbinghaus experiments on himself
German psychologist Hermann Ebbinghaus wanted to scientifically measure memory. With no modern equipment, he ran the experiment on himself. For months, he learned meaningless syllables ("BAJ", "ZUF", "QOK"…) then measured the savings on relearning: how much less time it took to relearn an already-forgotten list compared to learning it the first time. The result, published in 1885, founded the entire psychology of memory. Here are the popularized figures from his study (the relearning savings, often presented as a share of memory kept):
- 20 minutes later: 60%
- 1 hour later: 45%
- 24 hours later: 30%
- 6 days later: 25%
- 31 days later: 21%
This decay is called the forgetting curve. Without review, the savings drop fast: by the next day, a list of context-free syllables takes almost as much effort to relearn as on day one. Brutal.
Why does your brain erase everything?
It's not a bug, it's a feature. Your brain receives a constant stream of information. If it kept everything at full bandwidth, it would saturate. So it has a strategy: it only keeps what seems useful, defined as "what comes back regularly". An isolated piece of info is tagged "noise" and erased. A piece of info that comes back 3, 5, 8 times is tagged "signal" and consolidated.
That's exactly what our article on memory mechanisms demonstrates: each retrieval strengthens synaptic connections. But retrieving too often is wasteful. Retrieving too late is ineffective. You need to hit the right timing.
Spaced repetition: breaking forgetting at the right moment
The idea is simple: review the information just before you're about to forget it. Each repetition flattens the curve and stretches the next interval.
- 1st review: 1 day after learning
- 2nd: 3 days later
- 3rd: 7 days later
- 4th: 14 days later
- 5th: 30 days later
- 6th: 90 days later
- 7th: 180 days later
These intervals are a common practical convention, not an exact sequence from a specific study: what matters is spacing them out more and more, not hitting these numbers to the day. After a few months, the info is solidly anchored for years. It's the opposite of last-night cramming, which consolidates for 48 hours before disappearing.
The Leitner system: 5 cardboard boxes, zero algorithm
German journalist Sebastian Leitner popularized the analog version of the method in 1972. You take 5 boxes. You write your flashcards (question on one side, answer on the other).
- Box 1: review every day
- Box 2: every 3 days
- Box 3: every week
- Box 4: every 2 weeks
- Box 5: every month
Golden rule: if you nail a card, it moves up one box. If you fail, it goes back to box 1. With 50 cards, you can maintain a whole vocabulary (languages, dates, capitals) with 10 minutes per day.
It's rudimentary but ruthless. Many medical, law and language students swear by it.
Anki is the application that digitized Leitner and optimized it with the SuperMemo SM-2 algorithm (created by Piotr Wozniak in 1987). The principle:
- After each card, you rate your ease (Again, Hard, Good, Easy)
- The algorithm calculates the optimal interval before the next review
- The more you succeed, the longer the interval (up to several years)
Anki is free on desktop and Android, paid once on iPhone (€25, openly used to fund the project). It's the absolute reference. Millions of medical students rely on it for their exams.
Alternatives: Quizlet (more visual), RemNote (integrated with Markdown notes), Mochi (clean aesthetics). But Anki remains unbeatable on scientific rigor.
3 beginner mistakes
1. Overloading. Starting with 200 new cards per day is guaranteed burnout. Aim for 10-20 new cards/day. You still build up 3,600 to 7,300 solid cards per year.
2. Cards that are too long. "What are the causes of World War I?" → too vague, impossible to grade. Prefer 5 targeted cards: "Date of the Sarajevo assassination?", "Country that declared war first?", etc. One card = one atomic fact.
3. Quitting after a bad day. The forgetting curve doesn't take breaks. If you skip 3 days, your backlog explodes and you lose motivation. The rule: 10 minutes a day, every day, beats 1 hour on Sunday.
QuizFury and spaced repetition
You can apply the principle without installing Anki, simply by using QuizFury as a review system:
- Bookmark your favorite quizzes and replay them at increasing intervals: 1 day, 3 days, 1 week, 1 month.
- Play the daily quiz (
/daily) to maintain a minimum dose of cognitive stimulation every day.
- Use the infinite flashcards mode to chain cards without pause, the algorithm prioritizes the questions you missed.
- Replay European Capitals Medium once a week for a month: you'll have all 50 capitals etched in.
The mistake is to play a quiz once and forget 60% within 24 hours. Spaced repetition means playing the same quizzes at well-calibrated intervals.
Conclusion: 10 minutes a day, years of memory
Spaced repetition isn't a trick: it's the only proven method to go from "I saw this info once" to "I know it by heart forever". Ebbinghaus discovered it on himself 140 years ago, and every modern study (Cepeda et al. 2006, Karpicke 2008) confirms its effectiveness.
To combine spaced repetition with other memory techniques, take a look at our memory palace (visual/spatial), active learning (which explains why testing is always more effective than rereading), and classic mnemonics. And if you want ready-to-memorize content, run the 20 most asked general knowledge questions.
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