Ebbinghaus Forgetting Curve
In short
The Ebbinghaus forgetting curve describes how newly learned material is forgotten over time without review – rapidly at first, then more slowly. It goes back to the self-experiments of Hermann Ebbinghaus published in 1885.
What is the Ebbinghaus forgetting curve?
The Ebbinghaus forgetting curve is a graph showing how the proportion of learned material you retain declines over time when you do not review it. Its defining shape is a steep drop immediately after learning that gradually levels off. It is one of the oldest quantitative curves in the psychology of memory.
Where does the curve come from?
The German psychologist Hermann Ebbinghaus studied forgetting in the 1880s through painstaking experiments on himself. He memorised long lists of nonsense syllables and used the savings method – measuring how many fewer repetitions he needed to relearn a list after various delays. He published the results in 1885 in "Über das Gedächtnis" (On Memory). In 2015, Jaap Murre and Joeri Dros replicated the study under modern conditions and confirmed the basic shape of the curve; intriguingly, they found a slight upward bump after about 24 hours, possibly an effect of sleep.
What does the curve mean for learning?
The curve is a starting point, not a verdict. Every review lifts retention back up and makes the subsequent decline shallower – which is exactly where spaced repetition and the spacing effect come in. If you revisit material just before it fades, the curve shifts upward with each session and retention becomes more durable. Be cautious with the popular percentages: figures such as "70% forgotten after 24 hours" come from Ebbinghaus's experiment with nonsense syllables in a single person and do not transfer unchanged to meaningful, well-structured study material. The robust takeaway is qualitative: without review, freshly learned material fades fast, and deliberate, spaced refreshing is the effective countermeasure.
Two technical points aid interpretation. In its original form the curve's vertical axis is not a simple percentage remembered but a "savings" score — the share of the original learning effort saved when relearning the same list. And modern accounts stress that the exact shape depends heavily on what is learned and how meaningfully it is encoded: well-understood, connected knowledge decays far more slowly than arbitrary nonsense syllables.
Sources
- Replication and Analysis of Ebbinghaus' Forgetting Curve (Murre & Dros, PLOS ONE, 2015) — PLOS (Public Library of Science)
- Distributed practice in verbal recall tasks: A review and quantitative synthesis (Cepeda, Pashler, Vul, Wixted & Rohrer, Psychological Bulletin, 2006) — American Psychological Association / PubMed (U.S. National Library of Medicine)