Why spaced repetition works
October 10, 2026
Spaced repetition means reviewing something right before you'd forget it, and waiting longer each time you get it right. It's one of the most tested ideas in learning research. Here's the evidence behind it.
Forgetting is fast, then slow
In 1885 Hermann Ebbinghaus memorized lists of nonsense syllables and tested how much he still knew hours, days and weeks later. Most of what he lost went in the first day. After that the loss slowed down. That shape is the forgetting curve, and it's why a review the next day does so much more than a review the next month.
Spacing beats cramming
In 2006 Nicholas Cepeda and colleagues pulled together 317 experiments from 184 published articles. Spreading study out over time beat doing the same amount all at once. They also found that the best gap between sessions got longer the further away the test was.
How long to wait
Two years later the same group tested it directly. More than 1,350 people learned a set of facts, reviewed them after a gap of up to three and a half months, and took a final test up to a year later. For a test a week away, the best gap was about 20 to 40% of the time until the test. For a test a year away, it was about 5 to 10%.
So with an exam three weeks out, the first review should come a few days after you learn something, not the night before.
Testing yourself is part of it
In 2006 Henry Roediger and Jeffrey Karpicke had students read short passages and then either read them again or write down what they remembered. Five minutes later, the students who reread did better. Two days and a week later, the students who had tested themselves remembered more. A flashcard is a small test every time you flip it.
How MindMaxer uses this
Your rating sets the next gap. A 1 comes back in about two minutes, a 3 tomorrow and a 5 in a week. Every 4 or 5 in a row doubles the gap. Cards you know drift further apart, and cards you miss stay close until they stick.
Sources
- Ebbinghaus, H. (1885). Über das Gedächtnis. Translated as Memory. A Contribution to Experimental Psychology (1913).
- 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.
- 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.
- Roediger, H. L., & Karpicke, J. D. (2006). Test-enhanced learning. Taking memory tests improves long-term retention. Psychological Science, 17(3), 249-255.