The Leitner System Explained: How the Flashcard Box Method Works

The Leitner system is a way of reviewing flashcards so that the cards you struggle with come up often and the cards you know well come up rarely. It was described by Sebastian Leitner, a German science journalist, in his 1972 book "So lernt man lernen" ("How to learn to learn"), and it's still one of the clearest ways to understand how spaced repetition works.

All you need is a set of flashcards and a box divided into compartments.

How the Leitner System Works

Every card starts in the first compartment. When you review a card and get it right, it moves forward one compartment. When you get it wrong, it goes all the way back to the first one, no matter how far it had travelled.

The trick is that each compartment is reviewed less often than the one before it. Cards in compartment 1 come up all the time. Cards in compartment 5 come up rarely. So a card you keep getting right drifts toward the back of the box and you see it less and less, while a card you keep missing stays at the front where you review it constantly.

That one rule, "right moves forward, wrong goes back to the start", is the whole system.

A Simple Leitner Schedule

Leitner's original box used compartments of increasing size: you reviewed a compartment when it filled up. Most people today use a fixed schedule instead, which is easier to keep track of. A common five-box version:

Box 1: every day.

Box 2: every 2 days.

Box 3: every 4 days.

Box 4: every 8 days.

Box 5: every 16 days. Get a card right here and you can retire it, or move it to a monthly box.

The exact numbers matter less than the principle: each box roughly doubles the gap of the one before it. That's what makes the intervals expand, which is the core idea of spaced repetition.

How to Set Up Your Own Leitner Box

1. Make your cards. One fact per card, question on the front, answer on the back. Cards that ask several things at once are hard to judge as simply right or wrong.

2. Label your boxes or piles. Five is a good number to start with. A shoebox with dividers works, as do five envelopes or rubber-banded piles.

3. Put every new card in Box 1.

4. Review the boxes that are due today. Say each answer out loud or write it down before you flip the card, so you're genuinely recalling it rather than recognising it.

5. Move each card. Right: forward one box. Wrong: back to Box 1.

6. Add new cards to Box 1 gradually. Adding too many at once floods the first box and makes daily sessions long.

Where the Leitner System Falls Short

The Leitner system was a brilliant idea for paper cards, but it has some real limits.

It's a lot of admin. You have to track which boxes are due on which day, move every card by hand, and keep the boxes in order. The bigger your deck, the more time goes into managing it instead of studying.

Every card in a box gets the same gap. A card you instantly knew and a card you barely scraped through both move to the same box and come back on the same day.

One mistake resets everything. A card that has reached Box 5 goes straight back to Box 1 after a single wrong answer, even if you just had a momentary lapse. That means reviewing it daily again for something you mostly know.

Leitner vs. Spaced Repetition Apps

Modern spaced repetition apps grew directly out of the same idea, but they schedule each card individually instead of in boxes.

Algorithms like SM-2 give every card its own "ease" score based on how you rate it: again, hard, good or easy. A card you find easy gets longer and longer gaps. A card you find hard stays on a shorter cycle. Instead of five fixed intervals, every card gets its own, adjusted after every review. For a plain-language breakdown, see How Spaced Repetition Algorithms Work.

The other difference is simply that the app does the admin. There's nothing to sort, no boxes to track, and no risk of forgetting which pile is due. You review the cards it shows you, rate them honestly, and the schedule takes care of itself.

Should You Use a Leitner Box or an App?

A physical Leitner box is a good choice if you have a small deck, like a few dozen cards for one exam, and you enjoy working on paper. It costs nothing and teaches you exactly how spaced repetition works.

Once your deck grows past a hundred or so cards, or you're studying several subjects at once, an app saves a lot of time. Space Repeat is free during the beta and schedules every card with the SM-2 algorithm, so you get the Leitner principle without moving a single card by hand. For a comparison of the main options, see The Best Spaced Repetition Apps.

If your notes are already written as "term - definition" lines, the free flashcard maker turns them into cards you can print for a paper Leitner box, or study straight away in the app.

The Bottom Line

The Leitner system comes down to one rule: cards you know move away, cards you miss come back. It's the simplest way to put spaced repetition into practice, and it works on paper. Its limits are the manual effort and the one-size-fits-all intervals, which is exactly what flashcard apps were built to fix.