Forgetting Curve Calculator
How much of what you studied last week is still in your head? Explore the Ebbinghaus forgetting curve — and watch how a few well-timed reviews change everything.
The math behind the curve
The chart models retention as exponential decay: R = e^(−t/S), where t is the time since your last review and S is the "stability" of the memory — how many days it takes to fade to about 37%. New material starts fragile. Every successful spaced review resets retention to 100% and multiplies stability, which is why the purple curve gets flatter with each dot while the red curve just keeps falling.
The practical lesson: reviewing at expanding intervals — a day later, then a few days, then a week or two — costs a fraction of the time of relearning, because you always catch the memory before it disappears. Read more in our guide to the science of spaced repetition.
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Frequently Asked Questions
What is the forgetting curve?
The forgetting curve, first measured by Hermann Ebbinghaus in 1885, describes how memory for new material decays over time when you never revisit it. The decline is steep at first — much of what you learn fades within days — then levels off. Its shape is usually modeled as exponential decay.
How do spaced reviews flatten the forgetting curve?
Each successful recall does two things: it resets your retention to near 100%, and it makes the memory itself more durable, so the next decline is slower. After a handful of well-timed reviews, material that would have vanished in a week can persist for months. That compounding effect is the entire basis of spaced repetition.
Is this calculator an exact model of my memory?
No — it's an illustration of the shape of forgetting, using a standard exponential-decay model. Real decay rates vary hugely with material difficulty, how well you learned it, and how it was reviewed. Modern algorithms like FSRS estimate these parameters per card from your actual review history, which is far more accurate than any one-size curve.
How do I apply this to my studying?
Don't schedule reviews by hand — use a spaced repetition system. Turn your notes into flashcards, and let the algorithm resurface each card right around the time you'd otherwise forget it. RemNote builds this in: flashcards live inside your notes and reviews are scheduled automatically.
