Ebbinghaus did not only ask what he could recall. He also timed how long it took to relearn a list until he knew it perfectly again. Relearning was always quicker than learning the first time. He called the time saved the savings.
Key idea
Savings (percent) = (first learning time − relearning time) ÷ first learning time × 100.
Worked example: Worked example
A list took 20 minutes to learn. A week later it took 8 minutes to relearn. What were the savings?
- Time saved: 20 − 8 = 12 minutes.
- 12 ÷ 20 = 0.6.
- 0.6 × 100 = 60 percent.
Answer: 60 percent savings.
Worked example: Another example
Learning took 30 minutes and relearning took 30 minutes. What does that tell you?
- 30 − 30 = 0 minutes saved.
- 0 percent savings: nothing was kept.
Answer: 0 percent: as if learning from scratch.
Why it works
Savings show that forgetting is rarely complete. A memory you can't pull up may still be partly stored, and a review rebuilds it fast. That is why short reviews work.
Common mistake
Giving up on a subject you "forgot." A quick review costs much less than the first learning.