Learning Retention Calculator
Estimate memory retention over time.
Higher = better retention
Results update as you type.
How it works
Memory fades over time in a predictable pattern, and this calculator estimates how much of what you learned you still retain using the Ebbinghaus forgetting curve. You enter the number of days since you learned something and a memory-strength value, and it returns the estimated percentage retained and forgotten. In the late 1800s, Hermann Ebbinghaus discovered that memory decays exponentially: we forget rapidly at first, then more slowly, following a curve. This model expresses retention as e raised to the negative ratio of elapsed time to a memory-strength constant, so retention drops quickly in the first days and then levels off. The memory-strength value represents how durable the memory is: a higher value means the information was learned more deeply or reinforced, so it fades more slowly. The key practical insight is spaced repetition — reviewing material just as you are about to forget it resets and strengthens the memory, flattening the curve so each review lasts longer. This is why cramming fails for long-term retention while spaced review succeeds, and it underlies flashcard apps and effective study schedules. The values here are illustrative rather than precise for any individual, since real retention depends on the material, how well it was learned, sleep, and review. Use it to understand the concept and motivate timely review. Enter the days elapsed and memory strength to estimate retention.
Retention = e^(−days ÷ memory strength) × 100
The Ebbinghaus forgetting curve models memory as decaying exponentially over time. Retention equals e raised to the negative of the days elapsed divided by a memory-strength constant, times 100. A larger memory strength means slower forgetting and higher retention at any given time.
Source:Ebbinghaus forgetting curve
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter days since learning.
- 2
Adjust the options
Adjust memory strength if they apply — sensible defaults are already set.
- 3
Read your result
Estimated retention updates instantly as you type — no button to press.
Frequently asked questions
What is the Ebbinghaus forgetting curve?
The forgetting curve, discovered by Hermann Ebbinghaus, describes how memory of newly learned information decays exponentially over time — rapidly at first, then more slowly. Without review, much of what we learn is forgotten within days. The curve is the basis for understanding memory decay and for techniques like spaced repetition that combat it.
How is retention calculated?
This model uses retention equals e raised to the negative of the days elapsed divided by a memory-strength constant, times 100 for a percentage. Retention falls quickly at first then levels off. A higher memory-strength value, reflecting deeper learning or reinforcement, slows the decay so more is retained at any given time.
What is spaced repetition?
Spaced repetition is reviewing material at increasing intervals, timed to just before you would forget it. Each review strengthens the memory and flattens the forgetting curve, so the information lasts longer before the next review is needed. It is far more effective for long-term retention than cramming, and it powers flashcard apps like Anki and effective study systems.
Why does cramming fail for long-term memory?
Cramming packs learning into a single session, creating a memory with low durability that decays quickly along the forgetting curve. You may pass a test the next day, but most of it fades within days. Spaced review over time builds stronger, longer-lasting memories, which is why distributing study sessions beats last-minute cramming for real retention.
How accurate is this estimate?
It illustrates the shape of memory decay rather than predicting your exact retention. Real forgetting depends on the material's complexity, how deeply you learned it, prior knowledge, sleep, and how often you review. Use this as a conceptual guide to appreciate how fast memory fades and to motivate reviewing material before too much is lost, not as a precise measurement.