Spaced Repetition: How to Remember Anything With 80% Less Study Time

Spaced repetition is a learning technique that schedules reviews of previously studied material at expanding intervals — review on day 1, then day 3, then day 7, then day 14, etc. The schedule is designed to catch each piece of information just before you would have forgotten it.

The system is implemented today through apps:

• Anki — free, open-source, the gold standard for serious learners
• SuperMemo — Piotr Wozniak’s original algorithm, more academic
• Quizlet — easier UX, popular with students
• RemNote — combines notes + spaced repetition

All use variants of the same underlying math: each successful recall increases the next interval (you don’t need to see it again for a while); each failed recall resets the interval (you need it again soon).

The numbers from Ebbinghaus’s original work (replicated many times since):

• Within 20 minutes: ~42% forgotten
• Within 1 day: ~67% forgotten
• Within 6 days: ~75% forgotten
• Within 31 days: ~79% forgotten — then it stabilises

The curve isn’t linear — it’s exponential. Most of the forgetting happens fast. Reviews timed at the right moments interrupt the curve and reset retention to near 100%, with each successful review extending the “safe” interval until the next.

SRS works extraordinarily well for:

• Vocabulary in any language (Anki was originally built for Japanese kanji)
• Medical school facts (medical students using Anki score higher on board exams, per multiple studies)
• Programming syntax + APIs
• Legal cases, formulas, anatomy
• Historical dates, names, geography
• Music theory, poetry, lines, scripts

SRS is less helpful for:

• Deep conceptual understanding (you need productive failure for that — see our piece on productive failure)
• Skills with motor / procedural components (you need actual practice)
• Creative thinking (cards can’t encode the generative process)

1. Pick an app

For most learners: Anki (free, the most-researched app, works on every platform). Quizlet for casual use. RemNote if you want notes + cards in one tool. The app matters less than the practice.

2. Make cards as you learn

Don’t batch card-creation. Create cards immediately after learning a new fact, while it’s fresh. The act of writing the card is itself a learning event. A few cards a day beats 100 cards once.

3. Atomic cards (one fact per card)

The most common beginner mistake: cramming multiple facts into one card. Break each card down to one atomic question with one atomic answer. “What’s the capital of Germany?” not “Capitals of Europe.”

4. Use cloze deletions for facts in context

Instead of Q/A pairs for sentences, use cloze deletion: hide one word from a sentence, the rest is the cue. The brain remembers facts-in-context far better than facts-in-isolation.

5. Review daily, briefly

15-20 minutes a day, ideally at the same time. The app schedules the cards — you just do what it shows you. Skip a day and your queue accumulates; skip a week and you’ll have hundreds of cards waiting. Daily consistency is the entire game.

6. Trust the algorithm

Don’t mark cards “easy” just to clear them. Don’t mark them “hard” to be safe. Rate honestly — the algorithm uses your ratings to set the next interval. Honest feedback produces optimal scheduling; sandbagging breaks the system.

Three structural reasons SRS is the best memorisation system ever invented:

• It matches the brain’s actual forgetting pattern. Cramming fights against biology — trying to hold everything in short-term memory. SRS works WITH biology, catching things just before they’d be lost.
• Effort is bounded. The daily 15-minute review is a fixed commitment. The knowledge base grows; the daily effort doesn’t. After a year of daily Anki, learners can have 5,000+ cards retained with the same daily time investment.
• The reviews ARE the learning. Active recall (forcing yourself to remember before seeing the answer) is dramatically more effective than re-reading. SRS makes active recall the daily practice.

Anki is the most powerful productivity tool I’ve ever used. — Michael Nielsen, quantum computing researcher

Spaced repetition makes a habit out of remembering — which makes everything else in your learning stack work better. Combined with productive failure (encoding) and deep work (practice), you have the complete expertise-building system. The BuildYourYear habit module handles the daily Anki review as one of your tracked habits — the streak counter takes care of the consistency, the algorithm takes care of the scheduling.

By month 6 of consistent practice, learners typically retain 90%+ of what they put into the system — a number that’s incomprehensible to anyone who’s only done conventional study.