Cramming has a reputation problem it doesn't deserve: it works. If your only goal is to pass a test tomorrow morning, a long session tonight will get you there. The trouble comes a week later, when almost all of it is gone. Then the next course, which builds on this one, starts without a foundation.
Spaced repetition is the alternative. Instead of studying something once for a long time, you come back to it several times, with gaps between sessions. It is one of the most thoroughly tested findings in the psychology of learning. Most students still don't use it, partly because it feels less effective than cramming while you are doing it.
This guide covers why spacing works, how long the gaps should be, and how to turn it into a routine without drowning in reviews.
The forgetting curve
In the 1880s the German psychologist Hermann Ebbinghaus spent years memorising lists of nonsense syllables and testing how quickly he forgot them. He found that forgetting is fastest right after learning and then slows down. A large share of new material can be lost within a day or two, and what survives fades more gradually.
His results have held up remarkably well. A careful modern replication produced a forgetting curve very similar to the original (Murre & Dros, 2015).
Ebbinghaus also noticed something more useful: each time he relearned a list, it took less effort, and he forgot it more slowly afterwards.
What the research says about spacing
The spacing effect is simple: the same amount of study, spread across several sessions, produces better long-term memory than the same study massed into one. It has been found across hundreds of experiments with vocabulary, facts, maths, motor skills and more (Cepeda et al., 2006; Carpenter et al., 2012).
A few findings stand out for students.
Spacing beats cramming even when total time is identical. In a flashcard study, spacing was more effective than cramming for 90% of participants (Kornell, 2009).
Learners usually believe the opposite. In the same study, 72% of participants thought cramming had worked better after the first session. Massed study feels fluent. Spaced study feels harder, because you have forgotten a little in between.
The forgetting is the point. Reviewing when a memory has started to fade forces effortful retrieval, and effortful retrieval strengthens memory more than easy repetition (Soderstrom & Bjork, 2015).
How far apart should reviews be?
The best answer comes from a study of more than 1,350 people who learned a set of facts, reviewed them after a gap of up to three and a half months, and were tested up to a year later (Cepeda et al., 2008). The ideal gap depended on how long they needed to remember the material:
You need to remember it for… | Space your first review about… |
|---|---|
1 week | 1 day later |
1 month | 1 week or so later |
2–3 months | 2–3 weeks later |
1 year | 3 weeks or more later |
As a proportion, the best gap was about 20–40% of the time until the test when the test was a week away, falling to about 5–10% when it was a year away. Two practical lessons follow. First, if your exam is months away, reviewing tomorrow is not enough on its own; you need later reviews too. Second, gaps that are too short waste more than gaps that are a little too long, so when in doubt, wait a bit longer.
Do the gaps need to expand, as most apps assume? The evidence is mixed. One study found that equally spaced reviews did at least as well as expanding ones for long-term retention (Karpicke & Roediger, 2007). What matters most is that there are gaps, that each review involves real recall, and that the reviews happen at all.
A starter schedule
For most coursework, this pattern works well and is easy to remember:
Day 0: learn the material and do a first quick recall at the end of the session.
Day 1: first review.
Day 3: second review.
Day 7: third review.
Day 14: fourth review.
Day 30, then every month or two until the exam.
Adjust as you go. If a review was easy, lengthen the next gap. If you struggled, shorten it and review the weak points sooner.
Three ways to run spaced repetition
1. A simple review calendar
Keep a table with one row per topic and columns for each review date. When you finish a new topic, fill in its review dates straight away (day 1, 3, 7, 14, 30). Each day, do whatever is due. This works well for essay subjects and broad topics that don't break neatly into flashcards.
2. The Leitner box
A paper flashcard system devised by the German science writer Sebastian Leitner in the 1970s. You need five boxes or envelopes:
Box | Review this box… |
|---|---|
1 | Every day |
2 | Every 2 days |
3 | Every 4 days |
4 | Every week |
5 | Every 2 weeks |
New cards start in box 1. Answer a card correctly and it moves up one box. Get it wrong and it goes back to box 1. Easy cards gradually move out of your way, and difficult ones keep coming back until they stick.
3. A spaced repetition app
Apps do the scheduling for you. Anki is the best known. It is free on desktop and Android, open source, and widely used by medical and language students. Its optional FSRS scheduler adjusts intervals to your own memory. Other options include RemNote, Quizlet and Mochi.
Whatever the app, the quality of the cards decides how well it works:
Make your own cards, or at least edit shared decks heavily. Understanding comes before memorising.
Keep each card small. One fact, one answer. The SuperMemo guide Twenty rules of formulating knowledge is still the best advice on writing good cards.
Use cloze deletions for definitions and lists, for example "Glucose is broken down to release energy in the {{c1::mitochondria}}", which Anki shows with the answer hidden.
Do your reviews every day. Ten minutes daily beats an hour on Sunday, and skipped days pile up quickly.
Add interleaving: mix it up
Spacing has a close cousin called interleaving: mixing different types of problems in one session instead of practising one type at a time. In one study, students who practised maths problems in a mixed order scored 63% on a test a week later, against 20% for students who practised in blocks. That was despite the mixed group finding practice harder and scoring lower during it (Rohrer & Taylor, 2007).
Mixing helps because exams don't label their questions. Blocked practice lets you apply the method of the day without thinking. Mixed practice makes you first recognise which method a problem needs. Once you have learned several related topics, build review sessions that shuffle them together.
A six-week exam plan
Here is how spacing can shape a revision period for a course with six main topics (A–F):
Week | New learning | Spaced reviews |
|---|---|---|
1 | Topics A and B | A and B after 1 and 3 days |
2 | Topics C and D | C and D after 1 and 3 days; A and B after a week |
3 | Topics E and F | E and F after 1 and 3 days; C and D weekly; A and B at 2 weeks |
4 | Mixed practice questions | Interleaved questions across A–F; revisit the weakest topic |
5 | Timed past papers | Mark papers and turn every lost mark into a flashcard |
6 | Final past papers | Light reviews of flashcards; protect your sleep |
Notice what is missing: a final week of frantic rereading. By then the material has been retrieved many times, which is the most reliable protection against blanking on the day.
Common mistakes
Starting too late
Spacing needs calendar time. Starting three days before an exam leaves no room for gaps. Start reviewing new material in the first week of term, not the last.
Making too many cards
A deck you avoid is worse than a small deck you use. Prioritise concepts you keep forgetting and facts you genuinely need. If daily reviews take more than about 30 minutes, add new cards more slowly.
Letting reviews pile up
Missing a few days is normal. Don't try to clear a mountain in one sitting. Pause new cards and work through the backlog over several days.
Memorising without understanding
Spaced repetition makes memories durable. It doesn't make them meaningful. Learn the idea first, with examples and explanations, and then use spacing to keep it.
Watch: spaced repetition explained
This video walks through the forgetting curve and shows a practical way to set up a spaced revision timetable with a spreadsheet.
Frequently asked questions
Is cramming ever a good idea?
A last review the night before an exam is fine, and it can top up recent material. The problem is relying on cramming instead of spaced study. Crammed material fades fast, and many subjects build on what came before.
How many reviews does something need?
It depends on the material and how long you need it. Most items need at least three or four spaced reviews to become durable. Apps handle this automatically by lengthening intervals as you keep getting a card right.
Should I use a shared Anki deck?
Premade decks can save time for standard material such as vocabulary or medical facts, but only for content you have already learned. Cards you don't understand are hard to remember and easy to forget. Delete or rewrite anything that doesn't make sense to you.
Does spacing work for skills, not just facts?
Yes. The spacing effect has been found for problem-solving, motor skills and concept learning, not only word lists. For skills, spread your practice sessions across days and mix problem types.
References
Carpenter, S. K., Cepeda, N. J., Rohrer, D., Kang, S. H. K., & Pashler, H. (2012). Using spacing to enhance diverse forms of learning: Review of recent research and implications for instruction. Educational Psychology Review, 24(3), 369–378. doi.org/10.1007/s10648-012-9205-z
Cepeda, N. J., Pashler, H., Vul, E., Wixted, J. T., & Rohrer, D. (2006). Distributed practice in verbal recall tasks: A review and quantitative synthesis. Psychological Bulletin, 132(3), 354–380. doi.org/10.1037/0033-2909.132.3.354
Cepeda, N. J., Vul, E., Rohrer, D., Wixted, J. T., & Pashler, H. (2008). Spacing effects in learning: A temporal ridgeline of optimal retention. Psychological Science, 19(11), 1095–1102. doi.org/10.1111/j.1467-9280.2008.02209.x
Karpicke, J. D., & Roediger, H. L. (2007). Expanding retrieval practice promotes short-term retention, but equally spaced retrieval enhances long-term retention. Journal of Experimental Psychology: Learning, Memory, and Cognition, 33(4), 704–719. doi.org/10.1037/0278-7393.33.4.704
Kornell, N. (2009). Optimising learning using flashcards: Spacing is more effective than cramming. Applied Cognitive Psychology, 23(9), 1297–1317. doi.org/10.1002/acp.1537
Murre, J. M. J., & Dros, J. (2015). Replication and analysis of Ebbinghaus’ forgetting curve. PLOS ONE, 10(7), e0120644. doi.org/10.1371/journal.pone.0120644
Rohrer, D., & Taylor, K. (2007). The shuffling of mathematics problems improves learning. Instructional Science, 35(6), 481–498. doi.org/10.1007/s11251-007-9015-8
Soderstrom, N. C., & Bjork, R. A. (2015). Learning versus performance: An integrative review. Perspectives on Psychological Science, 10(2), 176–199. doi.org/10.1177/1745691615569000
Discussion