Spaced repetition: how to schedule your reviews
Spaced repetition means reviewing material at growing intervals, such as one day, three days, a week and then two weeks after you learn it, instead of all at once. Each review comes just as you are starting to forget, which makes the memory last longer. It works best combined with active recall: test yourself at each review rather than rereading.
Why spacing works
Memory fades quickly after you learn something, then more slowly. Hermann Ebbinghaus measured this forgetting curve in the 1880s. Every time you successfully recall something, the curve flattens, so the next review can come later. A large review of the research found that spreading study sessions out consistently beats massing them together, and that the best gap grows with how long you need to remember (Cepeda and colleagues, 2006).
A schedule you can follow without an app
| Review | When |
|---|---|
| First | The day after the lecture |
| Second | Three days later |
| Third | One week later |
| Fourth | Two to three weeks later |
| Before the exam | In the final week |
If you get something wrong at a review, start its schedule again. If you know it cold, you can skip a step.
Spacing with an app
Apps like Anki schedule each card for you based on how well you answered it. They are excellent for large amounts of facts. For understanding-heavy courses, space your practice tests too: retake a unit's test a week after the first attempt, then again before the exam.
Spacing plus active recall
Spacing decides when you review, and active recall decides how. Rereading on a perfect schedule still only helps a little. Answer questions, work problems and use flashcards at each review.
Sources
- Ebbinghaus, H. (1885). Memory: A Contribution to Experimental Psychology.
- Cepeda, N. J. and colleagues (2006). Distributed practice in verbal recall tasks. Psychological Bulletin, 132(3), 354 to 380.
Questions students ask
What is the best spaced repetition schedule?
A good default is one day, three days, a week, then two to three weeks. The ideal gap grows with how long you need to remember.
Do I need an app for spaced repetition?
No. A calendar or a simple table works. Apps help when you have hundreds of flashcards.
Is spaced repetition the same as active recall?
No. Spacing is when you review, active recall is how. They work best together.
Can I use spaced repetition close to an exam?
Yes, with shorter gaps. Even two or three spaced reviews in the last two weeks beat one long cram.