ABC Tools
Spaced Repetition Simulator illustration

Spaced Repetition Simulator

Five copies of the same flashcard deck, five schedulers — SM-2 (Anki classic), an FSRS-style rule that reviews when recall hits your target, Duolingo-style half-life regression, a classic Leitner box system, and Pimsleur's fixed graduated intervals. Every card's memory follows the same stability/retrievability model (R = exp(−t/S)) and the same simulated student answers all decks, so differences in daily workload, observed retention and knowledge-per-study-hour come from scheduling alone. Drag the retention-target and seconds-per-review sliders to see the efficiency trade-off, not only the retention target.

Runs 100% in your browser — simulations are computed locally on your device.

Read the full guide to this tool

Notes

  • The spacing effect falls out of the model: reviewing a card after its retrievability has dropped boosts stability far more than reviewing while it is still fresh — the cramming-vs-spaced comparison isolates exactly this.
  • A card counts as "mature" once its interval reaches 21 days, the same rough cutoff Anki uses. Higher retention targets mean more reviews per day for the same deck — 90% is the common sweet spot.
  • Knowledge / hour = expected cards still known at the end ÷ study hours (reviews × seconds per review). The green row is the most efficient scheduler under your settings.
  • These are deliberately simplified caricatures for building intuition — not the production Anki/FSRS/Duolingo/Leitner/Pimsleur algorithms.
  • Runs 100% in your browser — nothing you type or practice leaves your device.

Explore the idea

This interactive demo needs JavaScript.

Read the full guide for the explanation behind it

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