The forgetting curve shows how memory for newly learned material declines over time: steeply at first, then more and more slowly.

Where it comes from

Hermann Ebbinghaus used himself as his only subject. He memorized lists of nonsense syllables to the beat of a metronome and relearned them after intervals from 20 minutes to 31 days, measuring his "savings": how much less effort relearning took. In commonly cited figures from his 1885 book Über das Gedächtnis, savings fell to about 58 percent after 20 minutes, about 44 percent after an hour and roughly a third after a day.¹ A 2015 replication at the University of Amsterdam, with one subject spending some 70 hours on the task, produced a very similar curve.²

Where it goes wrong

Training vendors often turn the curve into claims such as "employees forget 70 percent of training within a day." Ebbinghaus measured the effort needed to relearn meaningless syllables, a different quantity from how much people recall of meaningful content. Material that connects to what we already know typically fades more slowly.

Talent Takeaway

Plan for the curve. Revisit the key ideas of a session after a day, a week and a month, with a short question, a case or a quick conversation. Each review gives the memory a longer life.

¹ Ebbinghaus, H. (1885). Über das Gedächtnis: Untersuchungen zur experimentellen Psychologie. Duncker & Humblot. English edition: Ebbinghaus, H. (1913). Memory: A contribution to experimental psychology (H. A. Ruger & C. E. Bussenius, Trans.). Teachers College, Columbia University.

² 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

Further reading: 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.