What the Leitner System Is and Why Digital Apps Often Get It Wrong

The Leitner system isn't just a list of cards with review dates. It's a row of boxes—usually five.

You take a stack of cards. If you know a card, it moves one box to the right, and you see it less often. If you don't know it, it goes all the way back to the first box.

Sebastian Leitner described this method in 1972 in his book So lernt man lernen—a title that roughly translates as “how to learn to learn.” The idea still holds up because it's easy to keep in your head and just as easy to put into practice: all you need are paper cards, boxes, and a marker.

The apps I've found online that use the word “Leitner” in their marketing often work a little differently. They assign each card its own date. A miss may move a card back only one step instead of sending it to the start. And box 2 effectively just means, “show me this card in two days.”

Each card follows its own schedule, with its own next review time.

Those tools can be good too. They're just not quite the Leitner system anymore.

How the boxes work

Imagine five boxes on a table. New cards start in the first one—the working pile. A typical paper schedule might look like this:

• Box 1—every day
• Box 2—when it fills up, roughly every other day
• Box 3—when it fills up, roughly once a week
• Box 4—when it fills up, roughly every two weeks
• Box 5—when it fills up, roughly once a month

You don't have to use those exact intervals. You can have three boxes. You can have seven. The number of boxes is a matter of pace.

But the key stays the same: you work with a box as one complete pile of cards.

Say today is Tuesday. You take box 1 and go through every card. Then you put the box back. The cards you knew move to box 2. The ones you didn't know stay where they are.

On Wednesday, you work with box 1 again, and if box 2 is already full, you work with box 2 as well.

You finish today's stack of cards and close the box.

That's it.

You don't need to open an app to see what the algorithm decided you should review today.

The original method was physical. I first saw it in an ad for a set of English flashcards that you were supposed to sort into boxes. I wrote about it in Why I Built Leitiq—including why carrying a box like that around isn't very convenient, and why I wanted to preserve the same idea in an app.

The boxes are the schedule: cards in the first box need frequent review, while cards in the fifth can rest for weeks.

Why a miss sends a card back to box 1

If a card has already reached box 4, the system is effectively betting that you'll remember it even after a long break.

Got it wrong? Then the bet didn't pay off. The card hasn't settled into your long-term memory yet.

The card doesn't become “almost box 4.” It needs to be practiced again.

If you simply move the card back one box after a miss, the earlier successful reviews still remain part of its history. Maybe that makes sense. But the Leitner system deliberately doesn't focus on that.

The card goes back to where you'll work with it again.

At first, it's a little annoying when a word you “definitely knew” last month suddenly ends up in the first box.

That's the point.

Hard cards stay in the working pile. Easy cards gradually stop taking up your attention.

Modern calendar-based spaced repetition systems—Anki, FSRS, SuperMemo—usually work differently. A miss shortens the next interval, but the card doesn't lose its entire history.

That's a perfectly reasonable approach. It's just a different model of how memory works, not the Leitner box system.

A box is not a due date

Spaced repetition rests on a simple idea: review something before you forget it, and lengthen the interval when you remember the material well.

The Leitner system is just one way to organize those reviews.

Calendar-based SRS works differently: each card has its own next date. Today you study whatever the algorithm has marked for review. Tomorrow the list will be different.

You can steadily work through that list, or you can build up a backlog.

In the Leitner system, cards live together in a box. You work with a particular pile, finish it, and stop. The rest of the cards wait together until it's time to pick up that box again and test your memory.

That's why the physical Leitner system still makes sense for people who don't click with modern review systems. You can see the amount of work.

Modern spaced-repetition systems and algorithms such as FSRS (Free Spaced Repetition Scheduler) optimize the timing of the next review for each individual card. Leitner works differently—it organizes the study session itself.

And that's an important difference.

Leitiq offers both the Leitner box system and FSRS. Try both and decide for yourself which one works better for you.

If you can't describe today's session by saying, “today I studied box number two,” then you're probably not using the Leitner system. You're using a list of cards that are due for review.

What Leitiq keeps from the original system

I didn't want to build another calendar.

In Leitiq, a correct answer still moves a card forward. A miss sends it back to the first pile. New cards are added in small batches you choose yourself, rather than gradually spilling into a “new for today” list.

Most importantly, the unit of work remains a study session you can actually finish.

If you didn't have enough time to study properly today, you can leave the session unfinished and continue it the next day.

You go through your cards. Hard ones come back. Easy ones move on. When another box reaches the limit you've set, it's ready for review. You can also adjust the limit for each box.

Paper cards never reminded you at 11 p.m. that you still had 47 cards left. An app can do that—unless you draw a clear line under the study day.

That's what I wanted to preserve in Leitiq: not the appearance of five boxes, but the feeling of a completed study session.

No endless list. No debt carried into tomorrow.

Just a box of cards waiting for your next study session.