Definition · Training and development
Forgetting Curve
Definition
Forgetting curve is the term for how memory of newly learned information declines over time when it is not reviewed or used. Hermann Ebbinghaus first described it in 1885: forgetting is steep in the first hours and days, then levels off. For trainers, it explains why one-time training fades and why spaced review and practice matter.
Also called: Ebbinghaus forgetting curve, Curve of forgetting, Memory decay curve
Formula
R = e^(−t ÷ S), a common simplified model of the curve
- R
- Retention: the share of the material still remembered, from 0 to 1.
- t
- Time since learning or the last review.
- S
- Memory stability. It increases with meaningful content, practice and each well-timed review, which flattens the curve.
- e
- The mathematical constant, about 2.718.
Worked example
With S = 3 days, retention after 1 day is e^(−1/3) ≈ 0.72, and after 7 days e^(−7/3) ≈ 0.10. If a review on day 2 raises S to 10 days, retention 7 days after that review is e^(−0.7) ≈ 0.50. The numbers are illustrative: real retention depends heavily on the material and the learner.
What Ebbinghaus actually found
Ebbinghaus tested himself on lists of nonsense syllables and measured how much time he saved relearning a list after different delays. Savings fell quickly at first, with much of the loss within the first day, and then declined slowly over the following weeks. A 2015 replication by Murre and Dros reproduced the same general shape.
Two cautions for trainers. First, the experiment used meaningless material, which is forgotten faster than meaningful, well-understood content tied to a real job. Second, the widely shared claim that "people forget 70% of training within 24 hours" is not a finding you can attach to Ebbinghaus or to workplace training in general. The shape of the curve is reliable; precise percentages for your training are not.
Why it matters for workplace training
Most corporate training is still a single event: a two-day class, a one-hour module, a new-hire week on policies. The forgetting curve predicts that a large part of it will be gone by the time employees need it, especially for rarely used procedures. That shows up as errors, repeat questions to team leads and the familiar complaint that "training didn't work."
In high-volume settings, the effect is easy to see. Contact center agents trained on 40 call types in week one often handle only the most common 10 in their first month on the floor. When a rare one finally arrives, they have forgotten it. The fix is not more classroom time; it is review and use spaced over time, and good learning transfer to the job.
Five ways to flatten the curve
- [Spaced repetition](/glossary/spaced-repetition/). Review key points at growing intervals: for example after 1 day, 3 days, 1 week and 3 weeks. Each review is short.
- Retrieval practice. Make people recall and apply, through questions, scenarios and practice calls, instead of rereading. Recall strengthens memory far more than review alone.
- Use it on the job quickly. Schedule people to apply new skills within days of training.
- Make it meaningful. Connect content to real cases and why it matters; meaningful material is retained longer than isolated facts.
- Provide job aids for rarely used procedures, so people do not need to remember everything. A good checklist beats a forgotten module.
Microlearning is a practical way to deliver the short spaced reviews, often as two-minute quizzes in the workflow.
A worked example
A retail bank trains 300 branch staff on a new account-opening procedure in a 90-minute session. Six weeks later, audits find errors on about one in five new accounts. For the next rollout, the bank cuts the session to 60 minutes, adds a one-page job aid and sends five three-question quizzes over four weeks, each focused on the steps people miss most. Error rates in the first six weeks fall to roughly one in fifteen accounts. Learner time actually decreases, because the quizzes take less time than the 30 minutes that were cut.
Frequently asked questions
What is the Ebbinghaus forgetting curve?
It is a model showing how memory of new information declines over time without review. Ebbinghaus found forgetting is fastest soon after learning and then slows down.
How fast do people forget training?
Forgetting is fastest in the first hours and days, but the exact rate depends on how meaningful the content is, how well it was learned and whether it is used. Precise universal percentages are not reliable.
How do you improve training retention?
Use spaced reviews, recall-based quizzes and scenarios, quick application on the job, meaningful examples and job aids for rarely used tasks.
What is the connection between the forgetting curve and spaced repetition?
Spaced repetition is the main counter to the forgetting curve. Each review at the right time strengthens memory so it decays more slowly afterward.
Does the forgetting curve apply to skills as well as facts?
Yes, skills also decay without use, though well-practiced skills tend to last longer than isolated facts. Regular practice keeps them current.