The forgetting curve shows how memory fades after you learn something: fast at first, then more and more slowly. Hermann Ebbinghaus measured it on himself in 1885, using lists of nonsense syllables. Every well-timed review makes the next decline gentler, which is why spaced, self-tested review beats cramming. The popular claim that you forget 70% of everything within 24 hours is a misreading of his data.
You read a brilliant article on Sunday. On Monday you tell a friend about it and get two sentences in before the details go soft. By Friday you remember that it was brilliant, and almost nothing else. Nothing is wrong with your brain. You have just met the oldest finding in the science of memory.
This page explains where that finding comes from, what the original numbers actually say, which famous figures are wrong, and what really slows forgetting. You can also try it yourself: the chart below lets you add reviews and watch the curve change shape. It is part of our guide on how to learn, which collects every method that holds up.
What is the forgetting curve?
The forgetting curve is a graph of how much of something you have learned is still in memory as time passes. It drops steeply in the first hours and days, then flattens into a long, slow tail. Most of the loss happens early. What survives the first week tends to stick around for a long time.
Three things about it matter for anyone who wants to remember more:
- The shape is reliable. Fast early loss followed by slow late loss shows up across a huge range of materials and people.
- The speed is not fixed. How steep the curve is depends on what you learned, how well you learned it and what you did afterwards.
- Each review changes the next curve. After a good review, memory still fades, but more slowly than before. That is the whole idea behind spaced repetition.
Try it: flatten the forgetting curve yourself
Tap a day to schedule a review. Each review lifts recall back to the top, and the decline that follows is shallower than the one before. Try one review on day 1, then add day 3, day 7 and day 14, and watch the end of the line climb.
The forgetting curve, with and without reviews
Add reviews and watch each new curve fall more slowly.
Day 30 in the model: 3% with no reviews, 3% with your 0 review(s).
The pattern in the chart is the one that matters: a review does not just top memory back up, it changes how fast it drains. Four short reviews spread across two weeks leave far more behind on day 30 than one long session ever could.
What Ebbinghaus actually did
Hermann Ebbinghaus was a German psychologist who wanted to do something nobody had managed: measure memory with the precision of a physics experiment. He ran his experiments in two stretches, in 1879 to 1880 and 1883 to 1884, and published them in 1885 as Über das Gedächtnis (translated into English as Memory: A Contribution to Experimental Psychology).
He had no lab and no volunteers, so he used the only subject available: himself. To keep meaning and prior knowledge out of the results, he built a stock of about 2,300 nonsense syllables, each a consonant, a vowel and a consonant, like DAX, BOK or ZUP. He drew lists of 13 syllables, read them aloud at a fixed pace of 150 beats per minute, and repeated each list until he could recite it once, without hesitation and without error.
The clever part was how he measured what was left. Instead of asking "how many syllables can I still recall?", he waited, then learned the same list again and timed it. If relearning took less time than the first learning, some memory must have survived. He called the difference the savings. A savings score of 50% means relearning took half as long as learning did the first time.
Here is what he found for lists relearned after different delays (Ebbinghaus, 1885, chapter 7):
| Time since learning | Savings when relearning |
|---|---|
| 20 minutes | 58% |
| 1 hour | 44% |
| 9 hours | 36% |
| 1 day | 34% |
| 2 days | 28% |
| 6 days | 25% |
| 31 days | 21% |
Look at the gaps between the rows. Between 20 minutes and one hour, savings fell by 14 points. Between day 6 and day 31, a gap of almost four weeks, they fell by only 4. Ebbinghaus summed it up himself: forgetting is very rapid at the beginning and very slow at the end. That curve is the forgetting curve.
He also ran the first spacing experiment. Cramming a list with 68 repetitions in one sitting got him to the point where 7 more repetitions the next day restored it. Spreading just 38 repetitions over three days did the same job. Same result, little more than half the effort, simply by spreading it out (Ebbinghaus, 1885, chapter 8).
Did the forgetting curve hold up? The 2015 replication
A study with one subject, run by that subject, in the 1880s, sounds like exactly the kind of result that falls apart when someone checks. In 2015, Jaap Murre and Joeri Dros at the University of Amsterdam checked. Dros spent about 70 hours learning and relearning lists of Dutch-style nonsense syllables, again as the only subject, at the same delays Ebbinghaus used, from 20 minutes to 31 days.
The curve came back. In PLoS ONE, they reported that the new curve and Ebbinghaus's original shared many of the same characteristics, across more than a century and a different language. The biggest difference was at 31 days, where Dros saved much less than Ebbinghaus had. They also found a small bump around the 24-hour point, where retention was a little better than the smooth curve predicts, and suggested sleep may be the reason, while noting that this still has to be established.
The broader literature agrees on the shape. David Rubin and Amy Wenzel gathered 210 published retention data sets for a 1996 review in Psychological Review and found that a handful of similar functions, all with fast early loss and a long tail, described them well. The details vary. The shape does not.
Forgetting curve myths: what the numbers do not say
Search for the forgetting curve and you will find confident figures: you forget 50% in an hour, 70% in a day, 90% in a week. Most of them trace back to Ebbinghaus's table, read the wrong way.
Myth 1: "You forget 70% of what you learn within 24 hours"
Ebbinghaus's one-day figure is a savings score of about 34%. That does not mean he could recall only 34% of the list, and it certainly does not mean you lose 66% or 70% of what you learn. It means relearning took about two thirds as long as the first learning. Savings and recall are different measures.
It also describes nonsense syllables, learned by one man, to the bare minimum of one perfect recital. Meaningful material behaves differently. Ebbinghaus noticed this himself: memorizing stanzas of Byron's Don Juan took him roughly a tenth of the repetitions that the same number of nonsense syllables needed (chapter 5). In a modern study with ordinary prose passages, students who simply reread a text still recalled 54% of its ideas two days later (Roediger & Karpicke, 2006). A useful rule: be suspicious of any single forgetting percentage that does not say what was learned and how it was measured.
Myth 2: "There is one forgetting curve for everyone"
The shape is universal; the slope is not. A vocabulary list you crammed, a story you found gripping and a skill you practiced for months all fall at different speeds. So do the same facts for two different people. That is why it makes sense to test yourself, rather than trust a chart, to find out what you still know.
Myth 3: "Review on days 1, 3 and 7 and you are done"
There is no magic schedule. In the largest study of review timing, Nicholas Cepeda and colleagues taught more than 1,350 people a set of facts, gave them one review after a gap of up to three and a half months, and tested them up to a year later. The best gap depended on how long they needed to remember. For a test a week away, the ideal gap was roughly 20% to 40% of that week. For a test a year away, it was closer to 5% to 10% of the year (Cepeda et al., 2008). Short goals call for short gaps. Long goals call for long ones.
Myth 4: "Forgotten means gone"
The savings method exists precisely because forgotten material leaves a trace. A month after learning, Ebbinghaus still relearned his lists about a fifth faster than the first time, even though he could not recite them. That is good news for anyone who feels they have "lost" a language or a subject from school. Relearning is faster than learning.
What actually flattens the forgetting curve
Four habits have strong evidence behind them. They work best together.
1. Test yourself instead of rereading
Pulling an answer out of memory strengthens it far more than looking at it again. In Henry Roediger and Jeffrey Karpicke's 2006 study in Psychological Science, students read a short prose passage, then either read it again or wrote down everything they could remember. Five minutes later, the rereaders did slightly better (81% vs 75%). Two days later the result flipped: 68% for the self-testers against 54% for the rereaders. After a week it was 56% against 42%. The tested group remembered as much after a week as the rereaders did after two days, and they got no feedback on their answers at all (Roediger & Karpicke, 2006).
The catch: rereading feels better. In the same research, extra studying made students more confident they would remember, even as it made them remember less. If you want the full toolkit, our comparison of microlearning, spaced repetition and active recall goes deeper.
2. Space your reviews out
The spacing effect is one of the best-replicated findings in psychology. A review by Cepeda and colleagues pooled 839 comparisons from 317 experiments and found that spreading study out beats massing it together for long-term recall (Cepeda et al., 2006). Ebbinghaus's 38-versus-68 repetitions was the first hint of it. In the chart above, it is the reason each later review leaves a flatter line.
3. Make it mean something
Ebbinghaus chose nonsense syllables because meaning helps memory so much that it spoiled his measurements. Use that. Connect a new fact to something you already know, ask yourself why it is true, or explain it in plain words to someone else, which is the heart of the Feynman technique. Visual tricks help too: the memory palace pins abstract items to places you can picture.
4. Sleep on it
The small 24-hour bump in the Amsterdam replication fits a large body of research showing that sleep helps the brain consolidate new memories (Rasch & Born, 2013), though the replication's authors were careful not to claim it as proof. The practical point holds either way: a study session followed by a decent night is worth more than the same session followed by an all-nighter.
A simple review schedule you can actually keep
Because the best gaps grow with how long you want to remember, a good default is to start close together and stretch out. For something you want to keep for months, try this:
- Right after learning: close the page and recall the main points from memory. One minute is enough.
- The next day: test yourself again before you look anything up.
- A few days later: another quick self-test. Note what you missed.
- About a week later: review the misses, then test the whole thing.
- Then every few weeks: stretch the gap each time recall feels easy.
Treat it as a rule of thumb, not a law. If something comes back easily, wait longer next time. If it is gone, shorten the gap. Want a starting point? Our free memory test shows how your short-term memory behaves today.
Where NerdSip fits
We built NerdSip around the two habits that do the most against the forgetting curve: self-testing and spaced review. Every lesson ends with a question, so you retrieve what you just read instead of scrolling past it. NerdSip's spaced repetition system then brings material back over time: in the Repetition tab, Memory Mix builds review rounds from courses you finished in the last 30 days and puts the material you learned longest ago first. Memory Mix is part of the paid plans.
It is not a flashcard app, and it will not tell you the exact day a fact is about to fade. What it does is make the first step easy. Type any topic, even "the forgetting curve", and NerdSip generates a fact-checked five-minute course on it, with a question at the end of every lesson.
The bottom line
Ebbinghaus's curve has survived 140 years and a modern replication. Forgetting really is fast at first and slow later. But the scary percentages that travel with it describe nonsense syllables measured in an unusual way, not the article you read on Sunday. You cannot stop the curve, and you do not need to. Test yourself, space it out, give it meaning, sleep on it, and each new curve will fall a little more slowly than the last.
Read next
References & Further Reading
- Ebbinghaus (1885), Memory: A Contribution to Experimental Psychology (English translation 1913), Classics in the History of Psychology
- Murre & Dros (2015), Replication and Analysis of Ebbinghaus' Forgetting Curve, PLoS ONE
- Rubin & Wenzel (1996), One hundred years of forgetting: A quantitative description of retention, Psychological Review
- Roediger & Karpicke (2006), Test-Enhanced Learning: Taking Memory Tests Improves Long-Term Retention, Psychological Science
- Cepeda, Pashler, Vul, Wixted & Rohrer (2006), Distributed practice in verbal recall tasks: A review and quantitative synthesis, Psychological Bulletin
- Cepeda, Vul, Rohrer, Wixted & Pashler (2008), Spacing Effects in Learning: A Temporal Ridgeline of Optimal Retention, Psychological Science
- Rasch & Born (2013), About Sleep's Role in Memory, Physiological Reviews
Frequently Asked Questions
What is the forgetting curve?
The forgetting curve shows how memory for something you have learned declines over time: steeply in the first hours and days, then more and more slowly. The German psychologist Hermann Ebbinghaus first measured it and published his results in 1885.
What is the Ebbinghaus forgetting curve?
It is the original curve from Ebbinghaus's experiments on himself. He learned lists of 13 nonsense syllables, relearned them after delays from 20 minutes to 31 days, and measured how much time the relearning saved. The savings fell from 58% after 20 minutes to about 34% after one day and 21% after a month.
Do we really forget 70% of what we learn within 24 hours?
No. That figure is a misreading of Ebbinghaus's one-day savings score of about 34%, which measures how much faster relearning was, not how much he could recall. It also comes from nonsense syllables. Meaningful material fades more slowly: in one study, students who simply reread a prose text still recalled 54% of its ideas two days later.
How do you beat the forgetting curve?
You cannot stop forgetting, but you can slow it down. Test yourself instead of rereading, spread your reviews over days and weeks, connect new material to what you already know, and sleep well after learning. Each good review makes the following decline shallower.
How often should I review something so I do not forget it?
There is no single schedule. A good default is to review the next day, a few days later, about a week later and then every few weeks, stretching the gap whenever recall feels easy. Research by Cepeda and colleagues found that the best gap grows with how long you need to remember.
Has the forgetting curve been replicated?
Yes. In 2015, Jaap Murre and Joeri Dros repeated Ebbinghaus's experiment with a single subject, about 70 hours of learning and the same delays. The resulting curve, published in PLoS ONE, shared most of the original's characteristics.
Every NerdSip course clears a four-layer fact-checking pipeline before it reaches the app: grounded in live sources, scored nightly, gated on failure, and reviewable by a person at one tap. Articles on this blog are drafted with AI assistance, then researched, verified, and edited by our team.
Editorial responsibility: ai51 UG (haftungsbeschränkt). Responsible editor named in the imprint.
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