Spaced repetition: how it works, and how to use it for exams

The forgetting curve

In the 1880s Hermann Ebbinghaus measured how fast he forgot lists he had learned. Memory fell steeply at first and then levelled off, and each time he relearned a list it faded more slowly. That curve is the whole idea: every well-timed review makes the next one wait longer.

Testing beats rereading

Rereading feels productive because the material looks familiar. Familiar isn't the same as remembered. Pulling an answer out of memory, as you do with a flashcard, strengthens it far more than reading it again, a finding known as the testing effect or retrieval practice.

How a scheduler decides when

After each card you say how it went. The scheduler uses that to estimate how well you know the card and when you're likely to forget it, and brings it back just before then. Easy cards drift months apart; hard ones come back within days.

• SM-2, from SuperMemo in the late 1980s, multiplies each interval by an ease factor that rises and falls with your answers. Anki used it for years.
• FSRS, the Free Spaced Repetition Scheduler, is open source and models each card's stability, difficulty and the chance you still remember it. You pick the retention you want, such as 90%, and it schedules for that.

In the benchmark its authors publish, FSRS predicts what you'll remember better than SM-2, which means fewer reviews for the same result. FlashCardz schedules every card with FSRS, aiming for 90% retention.

Spaced repetition before an exam

Spacing works best when it has time. Start a course's cards early and a few minutes a day carries them to the exam. If the exam is next week, spacing still beats one long night, and you can always add a last cramming session on top.

FlashCardz plans around your exam dates: the course with the nearest exam comes first, and missed cards come back sooner.

Making it a habit

• Review every day, even briefly. Ten minutes daily beats an hour once a week.
• Don't add too many new cards at once: each new card brings reviews with it for weeks. FlashCardz starts you at 25 a day.
• Answer honestly. Marking a card you missed as known only hides it from you until the exam.
• Take planned days off instead of skipping at random, so the schedule can work around them.

Questions