Spaced Repetition: What It Is, How to Space Your Revision, and a Ready Schedule and Tracker for Students

What spaced repetition means, in simple words

Think of a new fact as a path through a field of grass. Walk it once and the grass grows back. Walk it again before it fully grows back and the path gets clearer. Walk it a few more times, with longer and longer gaps, and it becomes a road you can find even after months.

Spaced repetition is that idea used for study. It has two parts. First, spacing: your reviews of one topic are spread over days and weeks, not packed into one evening. Second, repetition with growing gaps: every time you remember something well, you wait longer before the next review. When you forget it, you bring it back sooner.

The opposite is cramming, or massed practice: reading the same notes again and again in one long session, often the night before the test. The psychologist John Dunlosky describes this in an article for teachers: an eighth-grader reads his notes over and over the night before an exam until he feels ready. The alternative is to study the notes in a shorter session several evenings before, and then again the evening before. Dunlosky writes that students keep knowledge longer when they spread their practice out, even when the total time is the same.

Spaced repetition is about when you review. Active recall is about how you review: testing yourself with the book closed instead of re-reading. They work best together. This guide is about the timing; for the testing part, see our guide on active recall.

The forgetting curve: why you forget, and why spacing helps

In the 1880s the German psychologist Hermann Ebbinghaus tested his own memory. He learned lists of nonsense syllables (like made-up words) so that real meanings would not get in the way, and measured how much time he saved when he relearned a list later. This measure is called savings. If a list took 25 repetitions to learn the first time and only 20 to relearn a day later, he saved 5 out of 25, which is 20%.

He found that forgetting is fast at first and then slows down. Most of the loss happens in the first hours and day, and after that the memory fades more slowly. Drawn as a graph, this is the famous forgetting curve.

Is this old result still true? In 2015, Murre and Dros, working at the University of Amsterdam, repeated the experiment. One person spent 70 hours learning lists and relearning them after 20 minutes, 1 hour, 9 hours, 1 day, 2 days or 31 days. The results were similar to Ebbinghaus's own data. They also found the curve is not perfectly smooth: there was most probably a small jump upwards at the one-day point.

Why this matters: memory fades fastest at first, so the first review should come within a day; after each review forgetting slows, so the next gaps can be longer. The official Anki manual adds that Ebbinghaus reported this spacing effect in 1885: we remember better when reviews are spread out over time.

What the research says, honestly

• A big review in 2006. Nicholas Cepeda and colleagues pulled together 839 tests of spaced practice from 317 experiments in 184 published articles. Spaced study beat massed study, and the best gap between sessions depended on how long you need to remember: the longer the time until the test, the longer the best gap.
• A large study in 2008. The same team taught a set of facts to more than 1,350 people, gave a review after a gap of up to 3.5 months, and tested them up to one year later. Making the gap longer helped at first and then slowly hurt. For a test one week away, the best gap was about 20 to 40% of that week. For a test one year away, it was about 5 to 10% of the year.
• A review of ten study methods in 2013. Dunlosky and four colleagues judged which common study methods work. In his article for the American Federation of Teachers, Dunlosky says they rated two methods as the most effective: practice testing and distributed (spaced) practice. They work for students of different ages and many kinds of material. Highlighting and re-reading were found to be not that effective.
• Spacing feels worse but works better. In a 2008 study by Nate Kornell and Robert Bjork, people learned to recognise painters' styles. Seeing one painter's works spaced out (mixed with others) led to better results than seeing them together, yet participants rated the massed way as more effective, even after their own test showed the opposite.

Now the honest part. Not every study finds a big effect in real life.

• In a 2022 classroom trial, Foot-Seymour and Wiseheart gave school teachers lesson plans taught either one per day or one per week. The results were mixed. The authors say the noise of a real classroom may hide spacing effects that are clear in the lab.
• In a 2025 trial with medical residents in France, one group was invited to use a flashcard app. Only 67% of them even logged in, and only 45% of all residents did the final test. At six months there was no significant difference between the two groups. The authors think the reason is that many students did not really use the app.
• A 2024 paper by Veronica Yan, Faria Sana and Paulo Carvalho warns that cognitive science can guide study choices but cannot give one rule for everyone. The right timing depends on the content, the student and the goal.

The lesson: spacing works when you actually do the reviews. An app or a timetable you ignore does nothing.

How long should the gaps be?

There is no single perfect schedule. The 2008 Cepeda study gives a useful rule of thumb: the best gap is a share of the time until your test, and that share gets smaller as the test gets further away. About 20 to 40% when the test is a week away, about 5 to 10% when it is a year away.

Turn that into days. For a test in 7 days, 20 to 40% is roughly 1.5 to 3 days. For a test in 365 days, 5 to 10% is roughly 18 to 36 days. Tests in between sit in between. Remember that this came from one study of facts, so treat it as a starting point and adjust.

Two rules matter more than exact numbers. One: the first review should come within a day, because that is when forgetting is fastest. Two: if you get something wrong, shorten its gap; if you get it right easily, lengthen it. Software does this for you; on paper, a Leitner box does it (more on that below).

Four ways to run spaced repetition, and which to choose

You can space your reviews with a calendar, a box of paper cards, or an app. Pick the one you will really use. Here are four common ways.

1. A fixed list of review days

Every topic gets the same review days, for example Day 1, 2, 5, 12 and 30 after you learn it. You write the dates in a tracker (there is one later in this guide). It is simple and works well for whole chapters.

2. The 2357 method, counted back from your exam

Birmingham City University describes the 2357 method: you review a topic at growing gaps of 2, 3, 5 and 7 days. It also shows how to use it backwards from an exam. Put a session the day before the exam. Count two days back from that session and put another. Then three days back, then five, then seven, which is your first session. Their example shows this fitting into about 18 days before an exam. It is a good plan when an exam is close and you are revising, not learning for the first time.

3. The Leitner box, on paper

The Anki manual says that in 1972 a German scientist, Sebastian Leitner, made spaced repetition popular with paper flashcards kept in a row of boxes. A card moves to the next box when you get it right and back when you get it wrong, so you can see at a glance how well you know it and when to review it. The manual also says this is a rough method: it cannot give an exact date for each card and does not handle cards of very different difficulty well. For most school students it is still more than good enough.

4. A flashcard app that schedules for you

Apps like Anki ask you a question, you say how well you remembered, and the app picks the next review day. The Anki website says it schedules the next review for when you are most likely to forget. The free computer version is available for Windows, Mac and Linux, and AnkiDroid for Android is free. In Anki's newer scheduler (FSRS), a setting called desired retention decides how hard the reviews are: the default of 90% aims for you to remember about 90% of cards when they come up. A lower setting means fewer reviews but more forgetting.

How to start spaced repetition: step by step

1. List what you must remember, and by when. Write each subject, its chapters, and your test or exam dates. This decides the length of your gaps.
2. Learn the topic properly first. Spacing cannot fix something you never understood. Read, listen in class, solve the examples, and make short notes. Our guide on how to make notes shows a simple method.
3. Turn the topic into questions. For each chapter write 10 to 20 short questions: definitions, formulas, steps of a process, dates, reasons. These become flashcards or a question page. Keep one idea per question.
4. Do the first review within 24 hours. Close the book and answer the questions from memory, out loud or on rough paper. Then check. Mark each question: got it, shaky, or wrong.
5. Write the next review dates. Use your schedule from the table above, or move cards in your Leitner box. Wrong items come back tomorrow, whatever the schedule.
6. Review a little every day. Keep a short daily slot, for example 20 to 30 minutes, just for due reviews, before you start new work. Short and daily beats long and once a week.
7. Check your load every week. If reviews take too long, add fewer new cards for a few days. If they feel too easy, make the gaps longer. Fit the slots into your study timetable.

Good review is effortful. If you only look at the answer and think 'yes, I know this', you are re-reading, not reviewing. Always try to answer first, then check.

How to make a Leitner box from paper

You need some small cards (cut A4 sheets into eight), a pen, and five envelopes, boxes or rubber bands. Label them Box 1 to Box 5. Write a question on the front of each card and the answer on the back.

The rules below are one simple setup. Leitner's own system and later versions use different numbers, so change them if they do not suit you.

• Put a date on a sticky note on each box showing its next review day, so you do not have to remember.
• Say the answer aloud or write it on rough paper before you turn the card. Be strict: half right is wrong.
• Limit new cards to about 10 to 20 a day, so Box 1 does not overflow.

Worked example: one science chapter, 30 days

Meera is in Class 10. Her science teacher finishes the chapter on electricity on a Monday. Her term test is 30 days later. Here is how she uses spaced repetition, step by step.

Day 1, Monday evening (40 minutes). She reads her class notes once and solves two textbook examples. Then she writes 15 questions on small cards, such as 'What is the SI unit of electric current?', 'State Ohm's law', 'How do you find the total resistance of resistors in series?', 'Draw the symbol for a variable resistor', and one numerical problem. She closes her notes and answers all 15. She gets 9 right, 4 shaky and 2 wrong. All cards go into Box 1.

Day 2, Tuesday (10 minutes). She answers the 15 cards again before starting her homework. Now 12 are right. Those 12 move to Box 2; 3 stay in Box 1.

Day 3 onwards. Box 1 cards come up every day, Box 2 cards every second day, and so on, as the table below shows. The parallel and series circuit card keeps coming back to Box 1, so she asks her teacher about it, solves two more problems and makes a second card with a worked example.

Close to the test, she uses the 2357 idea backwards: full chapter reviews on Day 24, Day 27 and Day 29 (the day before the test), each with all cards and one past-paper style question.

In total Meera spends about three hours on this chapter across 30 days, in small pieces. A crammer might spend the same three hours the night before the test, feel confident, and forget most of it a week later. The research above suggests Meera's way leaves her far more for the final exam months later.

A ready spaced repetition tracker you can copy

If you prefer chapters and topics to cards, use this tracker in a notebook or a spreadsheet. One row per topic. Write the planned dates the day you learn the topic, and tick them as you go. Mark each review: G (good), S (shaky) or W (wrong). A W means the next review is tomorrow.

• Count your due reviews each morning. If more than you can do, do the oldest and the W items first.
• Every Sunday, look at the S and W column. Those topics need new practice, not only review.

How to use spaced repetition in different subjects

Spacing helps memory in every subject, but what you review changes. Here is what to put on your cards or question pages.

For maths and science, mix problem types in one review instead of doing ten of the same kind. This is called interleaving, and Dunlosky's group reviewed it as a separate method; Kornell and Bjork's painters study is one example of how mixing helps. For subjects with lots of reading, you can combine spacing with a reading method such as SQ3R.

Spaced repetition is not only for school. If you are learning a language, a programming skill or a craft, the same rule applies: short, regular practice with growing gaps. You can find free notes and courses to learn from, and then space your practice.

Common mistakes, and how to fix them

A last mistake is believing spacing is not working because it feels hard. Remember the Kornell and Bjork study: people judged massed study was better even when their own scores said the opposite. Feeling slow at the start of each review is normal. Judge the method by your test results after a few weeks, not by how it feels on one day.

When spaced repetition is not the answer

• When you have not understood the topic. Spacing helps you keep what you know. If a chapter makes no sense, first get help: ask your teacher, watch a lesson, or work through examples. Our guide on metacognition helps you notice when you do not really understand something.
• When the exam is tomorrow. You cannot space over one night. Do one round of self-testing on the most important points and sleep. Then start spacing for the next exam on the first day.
• For skills that need long, deep practice. Writing an essay, a long proof or a project needs focused time, not only short reviews. Use spacing for the facts and methods inside it.
• When you are exhausted or very stressed. Rest and talk to someone you trust. A study method is not a fix for health problems.

India's National Education Policy 2020 says school assessment should move away from testing rote memorisation towards regular, formative assessment of higher-order skills such as analysis, critical thinking and conceptual clarity. It also says Board exams should test core capacities rather than months of coaching and memorisation. Spaced repetition fits this if you use it for understanding: space your practice of explaining, solving and applying, not only of recalling words.

Review together on Sikhami

Sikhami is a social network for people in India who are learning, for every kind of learning. A few of its free tools fit spaced repetition well.

• Play quiz battles as a short, fun review on your planned days. You can pick subjects like maths, English or general knowledge.
• Join a live study room at the same time each day for your review slot, so a study partner keeps you regular.
• Read free notes shared by teachers and other learners, and turn the key points into your own questions.
• Find people learning the same subject in clubs and quiz each other on your review days.

See all of Sikhami's tools for you on the page for learners.