Leitner system: How to set up and run a flashcard box

A stack of 200 flashcards is too many to go through every day. Most of those cards don't even need a daily look. The Leitner system is a simple way to decide which cards to study each day. You sort your cards into a few real boxes, like shoeboxes, by how well you know each card. You open the box of cards you know well less often than the box of cards you keep missing.

That way, your study time goes to the cards you don't know yet, not the ones you've known for weeks.

Quick answer: What is the Leitner system?

• With the Leitner system, you sort your flashcards into three boxes based on how many times in a row you've answered each one correctly.

• The boxes are real containers, like shoeboxes or envelopes. You label them 1, 2, and 3. Flashcard apps can do the sorting for you on your phone.

• Every new card starts in box 1, which you study every day. When you answer a card correctly, it moves up to the next box. When you miss a card, it goes back to box 1.

• You open box 2 less often than box 1, and box 3 less often than box 2. For example, you might open box 2 three days a week and box 3 once a week.

What do you need to set up a Leitner box?

You need a pack of index cards and three containers. Shoeboxes work well. So does one recipe box with two cardboard dividers inside. Some people skip the boxes and keep three piles of cards held together with rubber bands. Label the containers 1, 2, and 3.

Box 1 holds new cards and cards you just missed. Box 2 holds cards you've answered correctly once. Box 3 holds cards you've answered correctly at least twice in a row.

Use one set of boxes for everything you're learning, even if you study more than one subject. One set means one schedule to keep. To remember where a card came from, like a language course or a book, put a small colored dot in its corner.

What should you write on each card?

Write one question on the front of each card and a short answer on the back. If you're learning a word, put the word on the front. On the back, write a short meaning and one example sentence.

Keep each card to one fact. Then, a correct answer means you know everything on the card. When you study, say or write your answer before you flip the card over. Answering from memory before you check is called active recall, and it's what makes flashcards work.

If you need a word both ways, like Spanish to English and English to Spanish, make two cards. You'll often know one direction well before you know the other.

Every deck has a few cards you keep forgetting. After you miss a card three times, rewrite it. You can split it into two smaller cards, or you can give it a memory hook from these mnemonic devices.

How do cards move between the boxes?

When you open a box, take out one card at a time, answer it from memory, and then flip it over to check. If your answer was correct, the card moves up to the next box. If you missed it, the card goes back to box 1, no matter which box it came from. Box 3 is your last box, so a card you answer correctly there stays in box 3.

Some guides move a missed card back just one box instead of all the way to box 1. Box 1 is the better choice. A card you just missed needs to come back tomorrow, and box 1 is the only box you open every day.

How often should you open each box?

Open box 1 every day, box 2 three days a week, and box 3 once a week. Pick fixed days and keep them. Then, you never have to decide which boxes to open.

The University of York's study guide suggests using three to five boxes. Three boxes are enough to start. Once box 3 gets crowded, you can add a box 4. Box 4 holds the cards you answer correctly in box 3, and you open box 4 every other Sunday.

How do you keep track of when a card moved?

Write the date on a card in pencil every time it moves up a box. The date shows how long the card has been in its new box. Without the date, a card can come up again too soon.

Say a card moves from box 2 up to box 3 on a Friday. Box 3's day is Sunday, so the card would come up again just two days later, even though box 3 is for cards you see once a week.

So when you open a box, look at the date on each card before you test it. Test a card in box 2 only if it has been there for at least two days. Test a card in box 3 only if it has been there for a full week. If a card hasn't waited long enough, leave it in the box until the next day you open that box.

What does a Leitner box look like over two weeks?

Over two weeks, the cards you know come up less and less, and the hard ones keep coming back. Here's an example with three English vocabulary cards, all started on the same Monday. The words are laconic (using very few words), gregarious (enjoying the company of other people), and ubiquitous (seeming to be everywhere).

The table leaves out the days when none of these three cards came up. A blank cell means that card's box wasn't opened that day. In two weeks, you saw laconic three times, gregarious four times, and ubiquitous five times. You never had to decide which word needed the most practice. The boxes decided for you. Ubiquitous starts over in box 1 on Monday, and that's normal. The word just needs a few more days.

How many new cards should you add each day?

Start by going through about 10 new cards a day. At that pace, a deck of 100 cards is all in your boxes within 10 days.

Box 1 tells you if you're going too fast. If box 1 has more than about 30 cards when you sit down, skip new cards that day and let box 1 shrink. If your daily study time feels short, you can add a few more new cards each day.

What should you do after you miss a few days?

After a break, don't start over. Open whichever boxes are due today. The cards in box 2 and box 3 just waited longer than planned. If you've forgotten some of those cards, you'll miss them when they come up, and they'll drop to box 1 as usual.

Don't add new cards until box 1 is back under about 30 cards. You don't need to go through every waiting card in one sitting.

Elevate, a brain training app, is built on the same two habits as a Leitner box: answering from memory and coming back to things after a gap. Unlike a box, Elevate's games adjust their difficulty to how you're doing. Elevate Premium includes five memory games. In one of them, Retention, you practice using your short-term memory to recall lists of items. Premium also has a custom Vocabulary workout of three to five games. For a few minutes of memory practice on days away from your box, try Elevate's memory games.

Should you use a paper box or a flashcard app?

A paper box works well for up to a few hundred cards. Sorting the cards by hand takes only seconds, and you can watch each box fill up and empty out. York's study guide lists this drawback of the method: "It can be overwhelming to manage an extensive number of cards across multiple subjects."

Start on paper. When your daily study starts taking longer than you want to spend, switch to an app. Apps such as Anki do the sorting for you and work out how long to wait between reviews for each card, not for each box.

Does the Leitner system work?

The Leitner system combines two study habits with strong research behind them: testing yourself and spacing out your reviews. A 2013 review of 10 study techniques rated practice testing and distributed practice (spreading study out over time) as "high utility." We found no study of the Leitner box itself, but the box is just those two habits on a schedule.

The boxes also set the schedule for you, so you don't go by feel. And how a method feels can be wrong. In Nate Kornell's 2009 experiments, people studied flashcards either in one big stack or in several small stacks, one stack after another. The big stack put more time between each card's turns, and it worked better for 90% of the people in the experiments. Yet after the first study session, 72% of them believed the small stacks had worked better.

You'll also be tempted to drop the cards you think you know. In a 2008 study by Nate Kornell and Robert Bjork, people who were allowed to drop those cards learned a little less than people who kept studying every card. A Leitner box never lets you drop a card. Even the cards you know best come back once a week from box 3.

So keep the cards in your last box coming up, even after you're sure of them. In a 2008 vocabulary study, testing people again on words they had already recalled once "produced a large positive effect" on how many words they remembered later.

Frequently asked questions

Who invented the Leitner system?

Sebastian Leitner invented the Leitner system. He described it in his German book So lernt man lernen, which translates as "How to Learn to Learn." The book first came out in the early 1970s.

How long does it take to learn 100 flashcards with the Leitner system?

The Leitner system takes about three weeks to get 100 cards through all three boxes if you add 10 cards a day and answer each one correctly. The last 10 cards go into box 1 on day 10, a Wednesday, and move to box 2 the same day. They move to box 3 on Friday, day 12, and get their first box 3 test on Sunday, day 21. Each miss adds a few days for that card.