The Forgetting Curve Explained: What Ebbinghaus Found

What Ebbinghaus did in the 1880s

Hermann Ebbinghaus published his book Über das Gedächtnis in 1885. In it he reported experiments on memory using nonsense syllables: made-up letter groups with no meaning, such as ZOF (an example of our own). He learned a series of them, waited, and then relearned the same series. The method is called a savings method (Ebbinghaus, 1913), and a free English translation from 1913 is available.

Savings means how much effort relearning spared him compared with learning from scratch. His delays ran from about one third of an hour up to 31 days. Murre and Dros (2015) describe him as testing himself, and the 1879-80 experiments comprised 163 double tests. Treat it as a classic small-sample dataset: one person, one kind of material.

The shape of the curve

In his data, forgetting was rapid at first and then became slower. The table gives the figures he reported, as stated in the translation. Read them as savings in relearning effort for nonsense syllables, not as the share of facts a person can recall.

The steepest drop comes early, and later drops are gentler. That pattern is the "curve". It is a description of one dataset.

A 2015 replication with one participant

Murre and Dros (2015) repeated the experiment using the method of savings. One person spent about 70 hours learning lists and relearning them after intervals from 20 minutes to 31 days. The results were similar to Ebbinghaus's original curve. The authors also concluded that the curve is not completely smooth and most probably shows a jump upwards starting at the 24-hour data point.

Two cautions apply. First, only one participant took part, and the material was nonsense syllables learned in a lab. Second, the best mathematical shape for the curve is still discussed, so no single formula should be treated as a law of forgetting. We did not read the results sections in detail, so we do not offer an explanation for the small jump.

What the curve does and does not tell you

Longer time spans and other material can look different. Bahrick (1984) tested 733 people on school Spanish across 50 years. Retention declined for the first 3 to 6 years, then stayed unchanged for up to 30 years before a final decline. That was an observational study of school Spanish, not a test of study methods, and it covered decades rather than the 31 days of the lab work above. We include it as a reminder that one short lab curve is not the whole story.

Spacing research is a separate body of work that asks a related question: when to review. In Cepeda et al. (2008), final-test performance first rose and then gradually fell as the gap between study sessions grew, and the best gap increased as the delay until the final test increased. That study used one kind of material, so it is not a personal schedule. What is spaced repetition covers the idea, and why you forget what you study lists the causes.

Try your own mini-curve today

You can measure your own forgetting informally. Pick a topic you studied yesterday, close the notes and write what you remember from a blank page. Then check and count the ideas you got. Repeat in a few days with the same topic. This is one data point from one person, so it shows your pattern for this topic, nothing more.

For ready-made practice, the forgetting and sleep deck has cards on these ideas. The wider picture is in how human memory works.

Common mistakes

• Quoting "you forget most of it in a day" as a fact. Ebbinghaus's numbers are savings in relearning nonsense syllables, from very few participants. Say what was measured.
• Reading the curve as a personal schedule. The curve describes one dataset. Use your own blank-page checks to see what you lose.
• Treating one formula as the law of forgetting. The best mathematical shape is still discussed. Stay with the description: fast early, slower later.
• Assuming the curve proves that spaced review works. The curve shows forgetting. The spacing evidence comes from separate studies, such as Cepeda et al. (2008).

Frequently asked questions

What is the forgetting curve?

It is a graph of how much relearning effort was saved after different delays. Ebbinghaus found that savings dropped quickly at first and then more slowly. It is a description of his data on nonsense syllables, not a universal law.

Is it true that we forget most of what we learn within a day?

The sources we read do not support one figure like that. Ebbinghaus reported savings of about one third after 24 hours, which is not the share of facts forgotten. Material, learner and test may all change the result.

Did anyone repeat Ebbinghaus's experiment?

Yes. Murre and Dros (2015) used the savings method with one participant, who relearned lists after 20 minutes to 31 days. The results resembled the original curve, with a small jump upwards from the 24-hour point.

Does the curve apply to my study material?

Possibly in part, but it was measured on nonsense syllables over up to 31 days, and other material over other time spans may look different, as in Bahrick's decades-long school Spanish study. Treat the curve as a reason to plan reviews, then watch your own results.

Sources

We opened each source below before citing it. See Methodology and Sources for how we check them.

1. Ebbinghaus, H. (translated by H. A. Ruger & C. E. Bussenius) (1913). Memory: A Contribution to Experimental Psychology. New York: Teachers College, Columbia University (English translation of Über das Gedächtnis, 1885). Open the source
2. Murre, J. M. J., & Dros, J. (2015). Replication and Analysis of Ebbinghaus' Forgetting Curve. PLOS ONE, 10(7), e0120644. Open the source
3. 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), 1-29. Open the source
4. 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. Open the source