What is the Leitner system, and how do I use it for revision?

How the boxes work

You need five boxes, envelopes or elastic-banded piles, labelled 1 to 5, and your flashcards. The method is usually credited to Sebastian Leitner, a German science writer who described it in the 1970s, and UK schools still teach it because it needs no screen and no app.

Every session follows the same steps:

• Take out the boxes due today. The timetable below says which.
• Shuffle each box, then answer every card out loud or on paper before you turn it over.
• Right: the card moves up one box. A right answer in Box 5 retires the card until your final run-through before the exam.
• Missed: the card goes back to Box 1, wherever it was.
• Add a few new cards to Box 1, ten a day at most.

Which box do I test on which day?

Box 1 every day, Box 2 every second day, Box 3 every fourth day, Box 4 every eighth day and Box 5 every sixteenth day. Spread out like this, you never test more than two boxes in a day, and the timetable repeats every 16 days: after Day 16, go back to Day 1.

Why the boxes work

Every session makes you pull answers out of memory, and the gap before a card comes back grows as you learn it. Those are the two revision methods with the strongest evidence behind them: a major review of ten common techniques gave "high utility" to only two of them, testing yourself and spacing your revision out, and rated re-reading and highlighting low.

Your effort also goes where it is needed. A card you have known for weeks costs you a few seconds once a fortnight, while a card you keep missing turns up every day until it sticks.

What if I miss a day?

Carry on from the day you missed: if you skipped Day 6, do Day 6 today and let the timetable move along by a day. What makes spacing work is that the gaps exist, and research comparing different spacing patterns found the exact pattern made little difference, so a day off undoes nothing. What does undo it is stopping for weeks and starting again the night before the exam.

How long before my exams should I start?

Earlier than you might think. A card you answer right every time still takes up to a month to work its way through all five boxes: a day in Box 1, then up to two days in Box 2, four in Box 3, eight in Box 4 and sixteen in Box 5. Cards you miss take longer. Starting six to eight weeks before your first exam gives most cards time to reach the top boxes and come round a few times.

Go easy on new cards, because every one comes back again and again. Anki's manual warns that learning 20 new cards a day means roughly 200 reviews a day once they start coming round, and paper boxes fill up the same way.

With less time than that, squash the timetable: test Box 1 every day and every other box every second day. The cards will not be spread as widely, but they will still come back, and the spaced repetition planner shows how much time a day your deck will need before the exam.

Should I use paper boxes or an app?

An app such as Anki runs the same idea for you, timing each card from how you answered it. That saves the bookkeeping, and it is worth it if you already revise at a laptop. Paper has one big advantage for many students: the phone stays in another room. A shoebox and five envelopes cost almost nothing and never send a notification.

Our printable Leitner box labels come with the 16-day timetable, and our blank flashcards print two-sided so each answer lands behind its question.