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How memory works

Why Do We Forget Things? The Science of Forgetting

By LaserMind Team ·

What is the forgetting curve?

In the 1880s, the German psychologist Hermann Ebbinghaus tested his own memory. He learned lists of nonsense syllables, relearned them after delays, and measured how much time the relearning saved compared with the first learning [4]. Plotting these "savings" against the delay gives the forgetting curve.

In 2015, Jaap Murre and Joeri Dros repeated the experiment: one person spent 70 hours learning lists and relearning them after delays from 20 minutes to 31 days, and the result was similar to Ebbinghaus's original data [4].

The shape is the useful part. In Ebbinghaus's data, as tabulated in the replication paper, relearning saved about 58% of the original learning time after 20 minutes, 34% after a day and 21% after a month: savings fell steeply over the first day and much more slowly over the following month [4].

Be careful with figures like "you forget 70% of a lecture in a day". Savings in relearning nonsense syllables is a different measure from the share of something you can recall: the replication paper points out that, in theory, a person could show full savings while recalling nothing on an ordinary test [4].

Why do we forget?

Researchers describe several causes. They often act together.

Later activity disrupts new memories

Classic theories blame interference between similar memories that share the same cues, studied in the lab with lists of word pairs [1]. In a 2004 review, John Wixted argued that this kind of interference may mainly explain forgetting in the laboratory; in everyday life, he proposed, forgetting comes more from new mental activity disrupting recent memories that have not yet had a chance to consolidate, even when the new activity is not similar to what you learned [1]. The same account, he noted, helps explain why sleep after learning improves memory for a recently learned list [1].

The memory is there, but you can't find it

Some forgetting is a failure to find a memory rather than a loss: recall depends partly on cues, and the place where you learned can be one of them [2]. A meta-analysis of studies on environmental context found that these effects were reliable, but they shrank when people had other cues to rely on, or when they mentally reinstated the original context at the test [2]. If an answer won't come, picturing where you were when you learned it is worth a try.

It was never taken in well

Some things are hard to recall because they were never processed much in the first place. In 1972, Fergus Craik and Robert Lockhart proposed a framework built on "levels of processing" [7]. A later series of ten experiments tested the idea by asking people questions about words: about their typeface (shallow), whether they rhymed with another word (intermediate), or whether they fitted a category or sentence (deep) [3]. On a surprise memory test, deeper encodings were generally remembered better [3].

Consolidation, and the role of sleep

A new memory is fragile at first and becomes more stable over time, a process called consolidation [1]. A major review describes an active role for sleep: recently formed memories are reactivated during deep, slow-wave sleep and integrated into long-term memory [8]. This is a model of the mechanism, not proof of any particular study tip.

The behavioural evidence is clearer. A meta-analysis of 177 articles found that people recalled more after a period of sleep than after the same time awake; the average effect was moderate, and smaller after correcting for selective reporting [9]. Read more in Sleep and memory.

Everyday forgetting is normal

Memory is often reliable, but it is also fallible [10]. In a well-known review, Daniel Schacter grouped memory's failures into seven "sins", three of which are kinds of forgetting: transience, absent-mindedness and blocking [10]. He argued that these failures are by-products of features of memory that are otherwise useful [10].

So forgetting a name, or why you walked into a room, is not on its own a sign that something is wrong.

When to talk to a professional. If memory problems are new, getting worse, worrying you or people close to you, or getting in the way of daily life, talk to a doctor or another qualified health professional. Memory can be affected by many things, and a professional can look at the whole picture. This article, and LaserMind's exercises, cannot assess or diagnose memory problems.

How to slow forgetting

A major review of study techniques rated two as the most useful, and both work against the forgetting curve [11].

  • Test yourself. Students who practised recalling a prose passage remembered substantially more of it two days and a week later than students who reread it, even though rereading looked better after five minutes [5].
  • Space it out. In a meta-analysis of 317 experiments, the best gap between study sessions grew with how long the information had to be kept [6].

Combining the two means recalling the material again on several different days. Spaced-repetition flashcards are built on this idea. For a practical routine, see How to improve memory for studying.

What the research says

◆ SupportedForgetting is fastest soon after learning and then slows, as in Ebbinghaus's data and the 2015 replication [4]. Testing yourself and spacing your study slow the forgetting of studied material [5][6].
◇ ConditionalSleep after learning helps retention, with a moderate average effect that shrinks after correcting for selective reporting [9]. The place where you learned can act as a cue; the effect is reliable on average but smaller when other cues are available [2].
✕ Not establishedThat practising memory games reduces everyday forgetting. A major review of brain-training studies found little evidence that training improves everyday cognitive performance [12].

Try it on LaserMind

▶ Recall Cards (spaced repetition)

Make cards from something you are learning and let the scheduler bring them back over the coming days.

Try it on LaserMind

▶ Object Recall

Study a set of objects, then pick out the ones you saw. Scores are compared only with your own history.

What research has not established

Ebbinghaus and the 2015 replication each tested a single person learning nonsense syllables. The replication matched the overall shape, but its savings after 31 days were much lower than Ebbinghaus's, and the authors could only speculate about why [4].

Why forgetting happens is still debated. Wixted's consolidation-based account of interference is one influential view, not a settled conclusion [1].

Classic findings also need checking. A famous 1975 experiment found that divers recalled word lists best in the setting where they had learned them, on land or underwater [13]. A 2021 replication with 16 divers did not find this [14].

Most of the studies here used laboratory materials such as word lists, usually with young adults and over short delays. Forgetting of complex material learned over months may follow a different course.

Frequently asked questions

If I've forgotten something, is it gone? Not necessarily. Ebbinghaus's savings method shows that material which seems forgotten can still be relearned faster than material that left no trace [4]. Some forgetting is also a failure to find the memory, as the research on retrieval cues shows [2].

Why do I forget things I read only yesterday? Forgetting is steepest in the first hours and days [4]. Testing yourself on what you read, rather than reading it again, helps more of it last [5].

What the research says

Last evidence check 2026-10-11
◆ Strong evidence

Students who practised recalling a text remembered more of it a week later than students who re-read it, even though re-reading looked better after five minutes. Daily life [5]

◆ Strong evidence

A review of ten common study techniques rated practice testing as one of only two with high utility. Daily life [11]

◆ Strong evidence

Across hundreds of experiments, spreading study over time beat cramming it into one session for later recall; the best gap grows with how long you need to remember. Daily life [6]

◆ Strong evidence

The same review of study techniques rated distributed practice as the other high-utility technique. Daily life [11]

◆ Strong evidence

A meta-analysis found that taking practice tests on studied material led to better learning than restudying it or other comparison activities, with the size of the benefit depending on the test and the study. Daily life [15]

◆ Strong evidence

A meta-analysis of the testing effect found bigger benefits when the practice test asked people to recall the material than when it only asked them to recognise it. Daily life [16]

References

  1. Wixted, J. T. (2004). The Psychology and Neuroscience of Forgetting. Annual Review of Psychology, 55(1), 235–269. https://doi.org/10.1146/annurev.psych.55.090902.141555
  2. Smith, S. M., & Vela, E. (2001). Environmental context-dependent memory: A review and meta-analysis. Psychonomic Bulletin & Review, 8(2), 203–220. https://doi.org/10.3758/BF03196157
  3. Craik, F. I. M., & Tulving, E. (1975). Depth of processing and the retention of words in episodic memory. Journal of Experimental Psychology: General, 104(3), 268–294. https://doi.org/10.1037/0096-3445.104.3.268
  4. Murre, J. M. J., & Dros, J. (2015). Replication and Analysis of Ebbinghaus’ Forgetting Curve. Plos One, 10(7), e0120644. https://doi.org/10.1371/journal.pone.0120644
  5. Roediger, H. L., & Karpicke, J. D. (2006). Test-enhanced learning: Taking memory tests improves long-term retention. Psychological Science, 17(3), 249–255. https://doi.org/10.1111/j.1467-9280.2006.01693.x
  6. 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. https://doi.org/10.1037/0033-2909.132.3.354
  7. Craik, F. I. M., & Lockhart, R. S. (1972). Levels of processing: A framework for memory research. Journal of Verbal Learning and Verbal Behavior, 11(6), 671–684. https://doi.org/10.1016/S0022-5371(72)80001-X
  8. Rasch, B., & Born, J. (2013). About Sleep's Role in Memory. Physiological Reviews, 93(2), 681–766. https://doi.org/10.1152/physrev.00032.2012
  9. Berres, S., & Erdfelder, E. (2021). The sleep benefit in episodic memory: An integrative review and a meta-analysis. Psychological Bulletin, 147(12), 1309–1353. https://doi.org/10.1037/bul0000350
  10. Schacter, D. L. (1999). The seven sins of memory: Insights from psychology and cognitive neuroscience. American Psychologist, 54(3), 182–203. https://doi.org/10.1037/0003-066X.54.3.182
  11. 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. https://doi.org/10.1177/1529100612453266
  12. Simons, D. J., Boot, W. R., Charness, N., Gathercole, S. E., Chabris, C. F., Hambrick, D. Z., & Stine-Morrow, E. A. L. (2016). Do "brain-training" programs work? Psychological Science in the Public Interest, 17(3), 103–186. https://doi.org/10.1177/1529100616661983
  13. Godden, D. R., & Baddeley, A. D. (1975). Context‐dependent memory in two natural environments: on land and underwater. British Journal of Psychology, 66(3), 325–331. https://doi.org/10.1111/j.2044-8295.1975.tb01468.x
  14. Murre, J. M. J. (2021). The Godden and Baddeley (1975) experiment on context-dependent memory on land and underwater: a replication. Royal Society Open Science, 8(11), 200724. https://doi.org/10.1098/rsos.200724
  15. Adesope, O. O., Trevisan, D. A., & Sundararajan, N. (2017). Rethinking the use of tests: A meta-analysis of practice testing. Review of Educational Research, 87(3), 659–701. https://doi.org/10.3102/0034654316689306correction
  16. Rowland, C. A. (2014). The effect of testing versus restudy on retention: A meta-analytic review of the testing effect. Psychological Bulletin, 140(6), 1432–1463. https://doi.org/10.1037/a0037559