Memory Retention Statistics (2026): How Fast We Forget

One day after learning a list of nonsense syllables, Hermann Ebbinghaus could relearn it in about two thirds of the original time, a savings of 33.7% (Ebbinghaus, 1885). A 2015 replication in PLOS ONE got 31.7% at the same delay. Those numbers measure relearning effort, not recall, and for real course material the forgetting is much slower: studies of classroom learning put typical retention at around 70% after one year.

This page collects the numbers people search for when they ask about information retention rates, with each figure checked against the study it came from and the limits of each study stated plainly.

Forgetting curve numbers: Ebbinghaus 1885 vs the 2015 replication

The forgetting curve drops steeply in the first hour and then flattens, and a modern replication reproduced that shape closely.

First, what the numbers mean. Ebbinghaus memorized rows of 13 nonsense syllables until he could recite them without error, waited, then relearned them. His measure was savings: the percentage of the original learning time he saved on the second attempt. A 33.7% savings score at one day means relearning took 66.3% as long as the first learning. It does not mean he could recall 33.7% of the syllables. Most websites that quote these percentages as "what you remember" get this wrong. Our full Ebbinghaus percentages breakdown covers the original tables in more detail.

• Ebbinghaus's savings were 58.2% after 20 minutes, 44.2% after 1 hour, 35.8% after 8.8 hours, 33.7% after 1 day, 27.8% after 2 days, 25.4% after 6 days and 21.1% after 31 days (Ebbinghaus, 1885, Section 28).
• In his own words: "One hour after the end of the learning, the forgetting had already progressed so far that one half the amount of the original work had to be expended before the series could be reproduced again" (Ebbinghaus, 1885, Section 29).
• Ebbinghaus doubted his own one-day figure, writing that 33.7% was probably "1 to 2 units" too high, but kept it because later tests supported it (Ebbinghaus, 1885).
• Jaap Murre and Joeri Dros replicated the experiment in 2015 with one subject (Dros, a native Dutch speaker) who spent about 70 hours learning and relearning 70 lists of 104 syllables each (Murre and Dros, 2015).
• The replication ran 10 lists per interval (9 at the 9-hour interval), against 12 to 45 per interval for Ebbinghaus, so its individual data points are noisier (Murre and Dros, 2015).
• Savings at 31 days were only 4.1% in the replication, far below Ebbinghaus's 21.1%. Correcting for learning times that crept up over the experiment raised it to 13.7%, still the largest gap between the two curves (Murre and Dros, 2015).
• In the replication, savings at 1 day (31.7%) were higher than at 9 hours (27.6%). Adding a one-day "boost" to a power-function fit raised the average variance explained across four datasets to 99.1%, and the authors note that sleep research would predict such a jump (Murre and Dros, 2015).
• When the replication also scored plain proportion correct, the forgetting curves were "much shallower than the savings curves", a reminder that savings and recall are different measures (Murre and Dros, 2015).

One more caveat before anyone applies these curves to a biology exam: both studies used meaningless syllables and a single, highly practiced subject. The forgetting curve explainer covers the theory; the rest of this page covers what happens with real material.

How much do students forget after a lecture or course?

Students forget course material far more slowly than Ebbinghaus forgot nonsense syllables: most studies find around 70% retained after a year.

• A review of classroom retention studies concluded that "approximately two-third to three-fourth of knowledge will be retained after one year, with a further decrease to slightly below fifty percent in the next year" (Custers, 2010).
• The same review treats 70% retention after one year as the modal value across disciplines as different as history, psychology and zoology, and reports around 30% retention of high school chemistry after four years (Custers, 2010).
• An earlier review of 62 studies of classroom learning found that "students retain much of what they are taught", that retention decreases over time, and that more original learning means better retention (Semb and Ellis, 1994). Custers (2010) summarizes that review as finding 84% retention when measured by recognition and 72% by recall.
• In a cross-sectional study of Dutch medical students and doctors, basic science scores fell from about 40% correct for students to 25% to 30% for doctors after many years in practice (Custers and ten Cate, 2011).
• In that study, little knowledge was lost for 1.5 to 2 years after it was last used, and retention sat at 15% to 20% after 25 years or more (Custers and ten Cate, 2011).
• When a 21-minute online statistics lecture was broken up with short quizzes, students in the second experiment (48 participants) reported mind wandering on 19% of probes, against 39% for a restudy group and 41% for an untested group (Szpunar, Khan and Schacter, 2013).
• On the final cumulative test in that study, the quizzed group scored 90% across all four lecture segments, compared with 76% for restudy and 68% for no quizzes (Szpunar, Khan and Schacter, 2013). The study had 80 participants across two experiments.
• A meta-analysis of 225 studies of undergraduate STEM courses found exam scores rose by about 6% under active learning, and students in traditional lectures were 1.5 times more likely to fail (Freeman et al., 2014).

Note what these studies measure. The course studies compare a later test with an end-of-course test, so "70% retained" means 70% of what was known at the end, not 70% of everything taught. The lecture studies measure test scores shortly afterward, not decay over months.

Long-term retention: Bahrick's "permastore" studies

Knowledge that survives the first few years can last for decades without any review, according to Harry Bahrick's long-term studies.

• Bahrick tested 733 people on Spanish they had learned in school, with retention intervals of up to 50 years (Bahrick, 1984).
• Retention declined exponentially for the first 3 to 6 years, then "remains unchanged for periods of up to 30 years before showing a final decline" (Bahrick, 1984).
• Learned responses either had life spans of 0 to 6 years or more than 25 years. None had life spans of 6 to 25 years, which Bahrick read as a discrete move into a "permastore" state (Bahrick, 1984).
• How much reached permastore depended on the level of original training and grades, not on rehearsal: most participants had used Spanish so little that the data showed no significant rehearsal effect (Bahrick, 1984).
• In a 9-year study, four subjects learned 300 English and foreign-language word pairs. 13 relearning sessions spaced 56 days apart produced retention comparable to 26 sessions spaced 14 days apart (Bahrick et al., 1993).

The Bahrick data are cross-sectional for the Spanish study (different people at different delays) and based on only four subjects for the vocabulary study. They are still the best evidence we have for what happens to school knowledge over a lifetime. For practical techniques that push material toward that durable state, see how to retain information in long-term memory.

What slows forgetting: retrieval, spacing and sleep

Testing yourself and spreading reviews out are the two best-supported ways to slow forgetting, and sleep soon after learning helps too.

Retrieval practice

• In Experiment 1 (120 students), rereading beat testing on a test given 5 minutes later (81% vs 75%), but testing won after 2 days (68% vs 54%) and after 1 week (56% vs 42%) (Roediger and Karpicke, 2006).
• In Experiment 2 (180 students), repeated testing produced 61% recall after a week versus 40% for repeated study, even though the study group read the passage 14.2 times and the test group only 3.4 times (Roediger and Karpicke, 2006).
• The study-only group was also the most confident it would remember the passage, despite forgetting 52% of its initial recall over the week (Roediger and Karpicke, 2006).
• Students learning 40 Swahili-English word pairs predicted they would recall about 50% a week later, whatever their condition. Actual recall ranged from about 80% with repeated retrieval to 33% to 36% without it (Karpicke and Roediger, 2008).
• The effect was large: d = 4.03, and the score ranges did not overlap (10% to 60% without repeated testing, 63% to 95% with it) (Karpicke and Roediger, 2008).

Spacing

• A meta-analysis of the spacing effect pooled 839 assessments from 317 experiments in 184 articles and found that the gap producing the best retention grows as the retention interval grows (Cepeda et al., 2006).
• In a follow-up with more than 1,350 people, study gaps of up to 3.5 months and final tests up to 1 year later, the optimal gap was about 20% to 40% of a one-week test delay and 5% to 10% of a one-year delay (Cepeda et al., 2008).
• Across three flashcard experiments, spacing beat massing for 90% of participants, but after the first session 72% believed massing had worked better (Kornell, 2009).

If you want to see what these curves imply for your own review schedule, the memory retention calculator estimates retention at different review gaps. And if the bottleneck is writing the cards in the first place, StudyCards AI turns a lecture PDF into a deck of retrieval-practice flashcards.

Sleep

• In two experiments with high school students (12 and 14 participants), vocabulary was remembered better when sleep followed "within a few hours of learning", independent of time of day (Gais, Lucas and Born, 2006).
• Students kept awake the night after learning remembered clearly less vocabulary at a retest 48 hours later, even after a night of recovery sleep (Gais, Lucas and Born, 2006).
• The one-day bump in both the original forgetting curve and its replication is consistent with a sleep effect, though Murre and Dros say this "remains to be established" for savings experiments (Murre and Dros, 2015).

For the mechanisms behind this, see our explainer on sleep and memory consolidation.

Popular memory retention myths

The two most repeated retention numbers online, "we forget 50% within an hour" and the learning pyramid percentages, are either distorted or have no source at all.

"We forget 50% of new information within an hour"

This is a distortion of Ebbinghaus. What he actually found is that after one hour, relearning a list of nonsense syllables took about half as long as learning it (44.2% savings). Three things get lost in the retelling:

1. It measures relearning time, not how much you can recall.
2. The material was meaningless syllables, the hardest kind of thing to retain.
3. It comes from one person testing himself in the 1880s.

Variants such as "50% within 30 minutes" or "70% within 24 hours" have no better source. No study we could find shows that people forget half of a lecture, article or meeting within an hour. For meaningful material, the classroom studies above point to around 70% retained after a year.

The learning pyramid (5% lecture, 90% teaching others)

The pyramid claims people retain 5% of what they hear in a lecture, 10% of what they read, and 90% of what they teach others. There is no study behind these numbers. Letrud and Hernes traced versions of the model back more than 160 years and concluded that "the models did not originate from empirical research" (Letrud and Hernes, 2018). What the research does support, that active methods such as self-testing beat passive rereading, is covered with real effect sizes in our study technique effectiveness statistics.

Methodology

We included only peer-reviewed research and primary texts: journal articles read via the publisher, PubMed, PubMed Central or ERIC, and the English translation of Ebbinghaus's 1885 book. Every number on this page was checked against its original source in September 2026. Where a source reports a number only in a figure, we left it out rather than estimate it. We did not use statistics roundup sites or secondary summaries, with one labeled exception: the recognition and recall figures for Semb and Ellis (1994) come from Custers's (2010) peer-reviewed summary of that review. Older landmark studies are included because they remain the primary evidence on long-term forgetting.

Sources

1. Ebbinghaus, H. (1885/1913). Memory: A Contribution to Experimental Psychology (H. A. Ruger and C. E. Bussenius, Trans.), Chapter 7. Teachers College, Columbia University. Classics in the History of Psychology
2. Murre, J. M. J., and Dros, J. (2015). Replication and analysis of Ebbinghaus' forgetting curve. PLOS ONE, 10(7), e0120644. doi:10.1371/journal.pone.0120644
3. Roediger, H. L., and Karpicke, J. D. (2006). Test-enhanced learning: Taking memory tests improves long-term retention. Psychological Science, 17(3), 249 to 255. doi:10.1111/j.1467-9280.2006.01693.x
4. Karpicke, J. D., and Roediger, H. L. (2008). The critical importance of retrieval for learning. Science, 319(5865), 966 to 968. doi:10.1126/science.1152408
5. Kornell, N. (2009). Optimising learning using flashcards: Spacing is more effective than cramming. Applied Cognitive Psychology, 23(9), 1297 to 1317. doi:10.1002/acp.1537
6. Cepeda, N. J., Pashler, H., Vul, E., Wixted, J. T., and Rohrer, D. (2006). Distributed practice in verbal recall tasks: A review and quantitative synthesis. Psychological Bulletin, 132(3), 354 to 380. PubMed 16719566
7. Cepeda, N. J., Vul, E., Rohrer, D., Wixted, J. T., and Pashler, H. (2008). Spacing effects in learning: A temporal ridgeline of optimal retention. Psychological Science, 19(11), 1095 to 1102. PubMed 19076480
8. Bahrick, H. P., Bahrick, L. E., Bahrick, A. S., and Bahrick, P. E. (1993). Maintenance of foreign language vocabulary and the spacing effect. Psychological Science, 4(5), 316 to 321. doi:10.1111/j.1467-9280.1993.tb00571.x
9. Bahrick, H. P. (1984). Semantic memory content in permastore: Fifty years of memory for Spanish learned in school. Journal of Experimental Psychology: General, 113(1), 1 to 29. PubMed 6242406
10. Custers, E. J. F. M. (2010). Long-term retention of basic science knowledge: A review study. Advances in Health Sciences Education, 15(1), 109 to 128. PubMed 18274876
11. Custers, E. J. F. M., and ten Cate, O. T. J. (2011). Very long-term retention of basic science knowledge in doctors after graduation. Medical Education, 45(4), 422 to 430. PubMed 21401691
12. Semb, G. B., and Ellis, J. A. (1994). Knowledge taught in school: What is remembered? Review of Educational Research, 64(2), 253 to 286. ERIC EJ488852
13. Szpunar, K. K., Khan, N. Y., and Schacter, D. L. (2013). Interpolated memory tests reduce mind wandering and improve learning of online lectures. Proceedings of the National Academy of Sciences, 110(16), 6313 to 6317. PMC3631699
14. Freeman, S., Eddy, S. L., McDonough, M., Smith, M. K., Okoroafor, N., Jordt, H., and Wenderoth, M. P. (2014). Active learning increases student performance in science, engineering, and mathematics. Proceedings of the National Academy of Sciences, 111(23), 8410 to 8415. PubMed 24821756
15. Gais, S., Lucas, B., and Born, J. (2006). Sleep after learning aids memory recall. Learning and Memory, 13(3), 259 to 262. PubMed 16741280
16. Letrud, K., and Hernes, S. (2018). Excavating the origins of the learning pyramid myths. Cogent Education, 5(1), 1518638. doi:10.1080/2331186X.2018.1518638

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Frequently Asked Questions

What percentage of information do we forget after 24 hours?

In Ebbinghaus's 1885 experiments, relearning a list after 24 hours took about two thirds as long as learning it the first time, a savings score of 33.7%. That is often rounded to "we forget 67% in a day", but it measures relearning time, not recall. For meaningful material, forgetting is usually much slower.

What is the average information retention rate?

There is no single rate. For course knowledge, Custers (2010) reviewed classroom studies and found students typically retain two thirds to three quarters of what they learned after one year, with 70% as the modal value, falling to 40% to 50% after two years and about 30% after four years or more.

Do we really forget 50% of new information within an hour?

Only in a narrow sense. Ebbinghaus found that after one hour he needed about half his original learning time to relearn a list of nonsense syllables (44.2% savings). He did not measure recall, and the figure applies to meaningless syllables. No study shows people forget half of a lecture or article within an hour.

How long do memories last without review?

Some last decades. Bahrick (1984) tested 733 people on Spanish learned in school up to 50 years earlier. Retention fell for the first 3 to 6 years, then stayed flat for up to 30 years before a final decline, even though most people had not used Spanish since school.

What is the fastest way to improve memory retention?

Test yourself instead of rereading. In Roediger and Karpicke (2006), students who took three recall tests remembered 61% of a passage a week later, versus 40% for students who reread it four times. Spacing reviews helps too: spacing beat massing for 90% of learners in Kornell (2009).