The Leitner system
Spaced repetition with a shoebox. Get a card right and it moves one box to the right, where it waits longer. Get it wrong and it goes back to box 1. Run the simulator to watch it happen.
Day 1: today you review boxes 1, 2, 3, 4, 5 (highlighted).
20 new cards start in box 1.
How to set up a Leitner box
- Make five compartments (a card box with dividers, five envelopes, or five rubber-banded piles) and label them 1 to 5.
- Put every new card in box 1.
- Review on schedule: box 1 every day, box 2 every second day, box 3 every fourth, box 4 every eighth, box 5 every sixteenth.
- Correct? Move the card up one box. Wrong? Back to box 1, no matter where it was.
- Graduate cards out of box 5 when you answer them correctly there, or keep them for occasional review.
That one harsh rule, wrong answers go all the way back, is what makes the system self-correcting: your time automatically flows to the cards you don’t know, while mastered cards cost almost nothing.
What the simulator shows
After a week or two, most cards gather in the higher boxes, and a typical day involves only a handful of reviews even though all 20 cards are still being maintained. Lower the “how well you know new cards” slider and you’ll see box 1 stay crowded: that’s the signal to split or rewrite cards that keep failing (tips in how to make flashcards).
Leitner vs a spaced repetition app
| Leitner boxes | App (SM-2) | |
|---|---|---|
| Interval | Set by the box (1, 2, 4, 8, 16 days) | Per card, based on its own history |
| Wrong answer | Back to box 1 | Interval restarts, ease factor lowered |
| Hard vs easy cards | Treated the same | Easy cards get longer gaps |
| Bookkeeping | You track which box is due | Automatic |
| Best for | Small decks, tactile learners, no screens | Large decks, long-term study |
The Cardsmith study session is essentially a Leitner system with infinitely many boxes, one per possible interval, run by the SM-2 algorithm. Prefer paper? Make your deck online and print it as flashcards to cut out.
The underlying reason both work is the forgetting curve: each successful review makes the memory last longer, so the next review can wait.
Questions people ask
What is the Leitner system?
A way of doing spaced repetition with paper flashcards and a set of boxes, introduced by German science journalist Sebastian Leitner in his 1972 book “So lernt man lernen”. Cards you answer correctly move to the next box, which you review less often; cards you miss go back to box 1.
How many boxes should I use?
Leitner’s original used five compartments. Three boxes are enough for a short course; five to seven suit long-term learning like languages. The key is that each box is reviewed roughly half as often as the one before.
How often do you review each box?
A common schedule is box 1 every day, box 2 every 2 days, box 3 every 4 days, box 4 every 8 days and box 5 every 16 days. Some people use weekday rules instead (box 1 daily, box 2 Mon/Wed/Fri, box 3 Tuesdays, and so on).
Is the Leitner system as good as a spaced repetition app?
It uses the same principle. Apps are more precise (every card gets its own interval, and difficult cards get shorter ones) and do the bookkeeping for you, but the paper version works well and many people enjoy handling physical cards.