A comprehensive training retention platforms designed to ensure technical workshop knowledge is applied, tracked, and reinforced in the field through structured follow-ups, field exercises, and supervisor oversight. Our Retain Apps flatten the Ebbinghaus Forgetting Curve.
Home of Hydra-Retain
Apps are in English and Espanol
The Forgetting Curve
The Ebbinghaus forgetting curve is a model showing how quickly memories fade after you first learn something. The drop is steep: within the first hour, you lose a significant portion of new information, and after a month, retention can fall to near zero for material you never revisited. The concept comes from experiments conducted by German psychologist Hermann Ebbinghaus in 1880, and it remains one of the most replicated findings in memory research.
How Ebbinghaus Discovered the Curve
Ebbinghaus wanted to study memory in its purest form, stripped of meaning and prior associations. To do this, he invented nonsense syllables, combinations of letters like “DAX” or “BUP” that had no built-in meaning. This was deliberate: real words carry emotional weight, personal connections, and varying levels of familiarity, all of which would muddy the results. He later verified his findings with more natural material like poems, but the nonsense syllables were the core tool.
He was also his own test subject. Ebbinghaus memorized lists of these syllables, then tested himself at various intervals to see how much effort it took to relearn them. His measurement method, called “savings,” was elegantly simple. If a list originally took 20 minutes to memorize but only 12 minutes to relearn the next day, that 40% reduction in effort was his savings score. Higher savings meant more memory had survived; lower savings meant more had been lost. By plotting these savings scores across different time intervals, the forgetting curve emerged.
How Fast You Actually Forget
The curve is not a gentle slope. It drops sharply in the first few hours, then gradually levels off. A 2015 replication study published in PLOS One by Jaap Murre and Joeri Dros closely followed Ebbinghaus’s original method and produced strikingly similar results, even though the replication was conducted in Dutch over a century later.
Here’s what the retention data looks like at each interval, measured as savings (the percentage of relearning effort saved compared to the original):
-
20 minutes: 44% retained
-
1 hour: 47% retained
-
9 hours: 28% retained
-
1 day: 32% retained
-
2 days: 23% retained
-
31 days: 4% retained
A few things stand out. The biggest drop happens between one hour and nine hours. And there’s a curious bump at the 24-hour mark, where retention actually ticks up slightly compared to nine hours. The researchers concluded this jump is a real feature of the curve, not random noise, possibly reflecting the role of sleep in consolidating memories. By 31 days, almost nothing remains of material that was learned once and never reviewed.
What Flattens the Curve
Ebbinghaus himself identified the most powerful countermeasure: spacing your review sessions over time. This is now known as the spacing effect, and it’s one of the most consistently replicated findings in all of cognitive psychology. When you revisit material at increasing intervals, say one day later, then three days, then a week, each review session resets the curve and makes the next drop less steep. Over several cycles, information that would have vanished in days can stick for months or years.
The reason spacing works is counterintuitive. The slight forgetting that happens between review sessions is actually productive. When you struggle to retrieve something you’ve partially forgotten, the act of retrieval strengthens the memory trace far more than simply rereading it while it’s still fresh. This is why cramming the night before an exam can get you through the test but leaves you with almost nothing a week later. You never gave your brain the chance to forget and recover, which is the cycle that builds durable memory.
Overlearning, continuing to practice material even after you can recall it perfectly, also slows the rate of decay. So does making the material meaningful. Connecting a new fact to a vivid image, a personal experience, or an existing framework of knowledge gives your brain more retrieval paths, which makes forgetting harder.