Spaced repetition is a study method that helps you remember information by reviewing it across several sessions over time. To use it, learn a topic, test yourself without looking at your notes, then return to it after a delay. Once you have a grasp of the subject, you can start by reviewing it 1, 3, 7 and 14 days after learning, adjusting the gaps to how well you remember and when your exam takes place.
You can use flashcards, practice questions or a blank sheet of paper. What matters is returning to the material and checking what you can recall before looking at the answer.
Spaced repetition helps reduce forgetting over time. The forgetting curve describes how retention of learned information declines over time, a pattern first studied systematically by Hermann Ebbinghaus.
For more on how information is retained, see our guide to long-term memory.
Why Does Spaced Repetition Help You Remember?
Something can feel familiar immediately after studying, yet be difficult to explain a week later. Reviewing after a gap helps you discover which information you can still retrieve and which parts need more work.
Research supports spreading learning across sessions. A meta-analysis by Cepeda and colleagues examined 317 experiments reported in 184 articles. It found that the gap between study sessions and the time until a final test jointly influenced retention.
A later study involving more than 1,350 participants investigated review gaps and final tests over longer periods. The most effective gap depended on how long participants needed to retain the information: longer retention targets generally called for longer gaps.
Cramming helps you remember for tomorrow. Spaced repetition helps you remember for longer.
How to Use the Leitner Box System
The Leitner system is a way to organise paper flashcards according to how well you know them.
Start new cards in Box 1. During a scheduled review:
- Correct answer: Move the card forward one box.
- Incorrect answer: Return the card to Box 1, check the answer and clarify anything you misunderstood.
One possible five-box arrangement is:
- Box 1: Review daily.
- Box 2: Review every three days.
- Box 3: Review weekly.
- Box 4: Review fortnightly.
- Box 5: Review monthly.
This gives difficult material more attention while reducing unnecessary repetition of answers you already know.
What is a flashcard?
A flashcard is a card (physical or digital) used to support memorisation. One side contains a question, and the other contains the answer.
For example:
- Front: How does photosynthesis work?
- Back: Photosynthesis is the process plants use to turn light, water, and carbon dioxide into glucose and oxygen.
My Experience With Spaced Repetition
When I was studying Econometrics, I noticed a real difficulty in remembering the maths around probability distributions, including the Gaussian, Exponential, Bernoulli, binomial, geometric, Poisson etc. I was really struggling to remember one, let alone the 10 required to be able to pass the paper. A friend of mine told me about spaced repetition.
So I tried this Leitner technique for 2 months before the final exam. On day zero, I would learn a new proof. Once I was happy, I would move that to Box 1. The next day, I would test whether I remembered the proof and, if I did, move it to Box 2. Each day, I would aim to learn a new proof and enter that into Box 1. I would keep repeating this every day until I had moved the proofs all the way up to Boxes 4 and 5 which meant I revisited them once a fortnight or month.
I found I ended up studying a lot less before the final exam and felt a lot calmer during it. I ended up passing with an A, one of the top marks in an incredibly challenging subject.
I can’t recommend this technique enough.
How Spaced Repetition Works with Active Recall
Active recall is a study method that improves memory by forcing you to retrieve information from your mind instead of simply rereading it.
In Roediger and Karpicke’s 2006 experiments, students who practised recalling prose passages remembered more on tests two days or one week later than students who repeatedly studied them. Repeated study performed better on the test after five minutes, showing why immediate familiarity can give a misleading impression of lasting learning.
Our guide to active recall explains how to use self-testing with your study material.
Spaced repetition tells you when to review.
Active recall tells you how to review.
Questions About Spaced Repetition
How Often Should I Review?
Begin with a short gap after learning, then adjust later reviews to your recall and deadline. Use the example schedule as a starting point, rather than treating its dates as rules.
Can I Use Spaced Repetition Without Flashcards?
Yes. Return to a topic using practice questions, explain a process aloud, or write what you remember on a blank page. Check your response afterwards and schedule another review.
What If My Exam Is Tomorrow?
A month-long schedule will not fit. Use the remaining time to answer important practice questions, correct weak areas and revisit them later if possible. For your next topic, begin spreading reviews out earlier.
Research Sources
- Cepeda NJ and colleagues. Distributed practice in verbal recall tasks: A review and quantitative synthesis. Psychological Bulletin, 2006.
- Cepeda NJ and colleagues. Spacing effects in learning: A temporal ridgeline of optimal retention. Psychological Science, 2008.
- Roediger HL and Karpicke JD. Test-enhanced learning: Taking memory tests improves long-term retention. Psychological Science, 2006.
- Murre JMJ and Dros J. Replication and Analysis of Ebbinghaus’ Forgetting Curve. PLOS ONE, 2015.