Ace
Short answer: the forgetting curve shows that memory fades fastest right after learning and then levels off. In Ebbinghaus's experiments, most of the benefit of learning was lost within a day. You flatten the curve by testing yourself instead of re-reading, reviewing at spaced intervals (for example 1, 3, 7 and 14 days later), and connecting new material to what you already know.
What is the forgetting curve?
In the 1880s, the German psychologist Hermann Ebbinghaus memorised lists of nonsense syllables and measured how much effort it took to relearn them after different delays. The less effort relearning took, the more he had kept. Plotted over time, the savings fall steeply at first and then flatten: that shape is the forgetting curve.
His numbers are striking. After 20 minutes, relearning saved him about 58% of the original effort; after an hour, about 44%; after a day, about 34%; after a month, about 21%. In other words, around two-thirds of the benefit was gone within 24 hours, and after that, forgetting slowed right down. Murre and Dros (2015) repeated the experiment more than a century later and found a very similar curve.
Do students really forget that fast?
Not always that fast. Ebbinghaus used meaningless syllables on purpose, and meaningful material like a lecture you understood is forgotten more slowly. But the shape holds: the steepest loss is in the first day or two, and anything you never revisit keeps fading. That's why a topic that felt clear on Monday can feel brand new in the exam.
How do you beat the forgetting curve?
1. Test yourself instead of re-reading
Pulling information out of memory strengthens it far more than reading it again. In Roediger and Karpicke's (2006) study, students who took practice tests forgot much less over a week than students who spent the same time re-reading. Close the notes and answer questions; check afterwards. More in active recall vs re-reading.
2. Space your reviews
Each time you successfully recall something after a gap, the next drop is slower. That's the idea behind spaced repetition: review just as you're starting to forget. Cepeda and colleagues (2008) found that the best gap depends on how long you need to remember: the further away the exam, the longer the gaps can be. Our spaced repetition schedule turns this into dates.
3. Make it mean something
Material you understand and connect to other ideas fades more slowly than isolated facts. Ask why each fact is true, link it to an example, and explain it in your own words. This is why learning anatomy by system works better than learning lists; see how to memorize anatomy.
A forgetting-curve plan for this week's lectures
- Same day: spend 10 minutes recalling the lecture's main points without notes, then fill the gaps.
- Next day: answer practice questions on it. This is where the curve is steepest, so this session matters most.
- Day 3 and day 7: quick question rounds, focusing on what you got wrong last time.
- Day 14, then monthly: mixed questions across several lectures until the exam.
The hard part is having good questions ready for every session. Ace builds them from your own lecture PDFs, slides or YouTube lectures and checks each one against the source, so your review sessions are a few taps away. Playing a quiz duel with a friend is an easy way to make the next-day session actually happen.
Frequently asked questions
How much do we forget after 24 hours?
In Ebbinghaus's classic data, about two-thirds of the benefit of learning was lost after one day. Meaningful material is usually forgotten more slowly, but the first day is still where most of the loss happens.
Is the forgetting curve still accurate?
Yes. A 2015 replication by Murre and Dros found a curve very close to Ebbinghaus's original. The exact numbers vary with the material and the person, but the shape is consistent.
What is the best way to stop forgetting what I study?
Combine self-testing with spaced reviews: answer questions from memory a day after learning, then again after a few days and a week. Each successful recall slows down the next round of forgetting.
Does sleep affect the forgetting curve?
Sleep helps consolidate new memories, so studying and then sleeping usually leads to better retention than pulling an all-nighter. It doesn't replace reviewing, though.
Sources
- Ebbinghaus, H. (1885/1913). Memory: A contribution to experimental psychology (H. A. Ruger & C. E. Bussenius, Trans.). Teachers College, Columbia University.
- Murre, J. M. J., & Dros, J. (2015). Replication and analysis of Ebbinghaus' forgetting curve. PLoS ONE, 10(7), e0120644.
- Roediger, H. L., & Karpicke, J. D. (2006). Test-enhanced learning: Taking memory tests improves long-term retention. Psychological Science, 17(3), 249–255.
- 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.
