StudyMinaSpaced Repetition: How to Remember What You Learn
Spaced repetition means reviewing material at increasing gaps. Learn how it works, what the evidence shows, and how to build a simple review schedule.
In this article
If you have ever crammed for an exam and found the material gone a fortnight later, you have met the forgetting curve. Spaced repetition is the standard answer to it: instead of studying something many times in one sitting, you review it at gaps that grow longer as the memory strengthens. This guide explains the idea, the evidence behind it, and a practical way to use it without any special software.
What spaced repetition is
Spaced repetition combines two ideas. Spacing means separating your study sessions in time instead of massing them together. Repetition means returning to the same material more than once. Put together, you learn a fact, review it soon after, then again after a longer gap, then a longer one still.
Researchers usually call the underlying finding the spacing effect or distributed practice. It is one of the most consistently replicated results in the psychology of memory.
Why we forget: the forgetting curve
In the 1880s the German psychologist Hermann Ebbinghaus tested his own memory for lists of nonsense syllables and found that forgetting is fastest soon after learning and then slows down. This pattern is now known as the forgetting curve.
A common simplified model describes the chance of remembering something after days as
where is a number describing how strong the memory is. A larger means slower forgetting. This is an illustration, not a law of nature, and real memory varies by person and material. But it shows the logic of spacing.
Suppose a fact has strength days. After one day, . After four days, , so you have probably lost it. Now suppose a well-timed review roughly doubles the strength to . Four days later, . The same four days now cost you much less. Each successful review makes the next gap safe to lengthen.
These numbers are toy values chosen to show the shape of the idea. They are not measurements of how your memory works.
What the evidence shows
In 2006, Nicholas Cepeda and colleagues published a review in Psychological Bulletin that pooled 839 assessments of distributed practice from 317 experiments in 184 articles. Their analysis found that the best gap between study sessions depends on how long you need to remember the material: the longer the retention interval, the longer the ideal gap.
That finding is practical. If your exam is next week, short gaps are fine. If you need to remember something for months, as you do for a cumulative exam or a professional qualification, longer gaps pay off.
Dunlosky and colleagues, reviewing ten learning techniques in 2013, rated distributed practice as one of only two “high utility” techniques, alongside practice testing. If you have not read it yet, our guide to active recall covers that other half. The two work best together: spacing tells you when to review, and recall tells you how.
A simple spaced repetition schedule
There is no single correct schedule. The following is a reasonable starting point for coursework, not one prescribed by research:
| Review | When to do it | What to do |
|---|---|---|
| First | Within a day of learning | Recall from memory, then check |
| Second | About 2 to 3 days later | Recall again, focus on what you missed |
| Third | About a week later | Recall again |
| Fourth | About 2 to 3 weeks later | Recall again |
| Later | Monthly until the exam | Keep missed items in rotation |
The key rule is what you do with mistakes. When you get an item wrong, bring it back to a short gap. When you get it right comfortably, let the gap grow.
Working backwards from an exam
If your exam is in six weeks, you can plan reviews backwards from that date. Learn each topic as it is taught, review it within a day, again after a few days, then again at roughly weekly intervals. Leave the last week for mixed practice and for items you keep missing. A timetable helps here, because reviews are easy to forget to schedule. See our guide to creating a weekly study timetable.
Doing it with paper: the Leitner box
You can run spaced repetition with index cards and a few boxes. This is called the Leitner system.
- Make a box for each review frequency, for example daily, every three days, weekly and fortnightly.
- Put all new cards in the daily box.
- When you answer a card correctly, move it to the next box. When you get it wrong, move it back to the daily box.
- Each day, review the daily box. On other days, review the box that is due.
It is simple, cheap and works offline. Its weakness is bookkeeping: it is easy to lose track of which box is due. Many students use flashcard software for this reason, and apps such as Anki schedule reviews automatically.
Does cramming ever make sense?
Sometimes. If a test is five minutes or one evening away, massed study can help, and Roediger and Karpicke’s classic experiment found that repeated studying beat testing on a five-minute delay. The problem is durability. Cramming gives you short-term access, not lasting knowledge, which matters for cumulative exams and for anything you will need to build on next semester.
If you are already close to an exam, do not despair. A compressed spaced schedule, even over three or four days, is better than one marathon session.
Common mistakes
- Spacing but not recalling. Reading your notes again at longer gaps is still rereading. Make every review an attempt to recall.
- Letting easy items dominate. Spend your effort on what you miss.
- Too many cards at once. Reviews pile up. Add new material at a pace you can keep reviewing.
- Starting too late. The advantage of spacing comes from having time. Begin as soon as you learn the material.
- Never adjusting. If you are forgetting a lot between reviews, shorten the gaps. If everything is easy, lengthen them.
Putting it together
Start small. Take the material from one course. Make a set of cards or questions. Review them the next day, three days later, a week later, then at longer gaps, always trying to recall before checking. Keep notes on what you miss. Within a couple of weeks you will see which topics are sticking and which need more attention, and you will have a routine that scales to other courses.
Sources
- 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
- Dunlosky, J., Rawson, K. A., Marsh, E. J., Nathan, M. J., & Willingham, D. T. (2013). Improving students’ learning with effective learning techniques. Psychological Science in the Public Interest, 14(1), 4–58. doi.org/10.1177/1529100612453266
- Roediger, H. L., & Karpicke, J. D. (2006). Test-enhanced learning: Taking memory tests improves long-term retention. Psychological Science, 17(3), 249–255. doi.org/10.1111/j.1467-9280.2006.01693.x
- Ebbinghaus, H. (1885). Über das Gedächtnis. Leipzig: Duncker & Humblot.
