We invented
Spaced Repetition

Spaced repetition began over 40 years ago, when Piotr Woźniak created the first computational algorithm to optimize learning.

1985: The Discovery
The initial mathematical model for the “Forgetting Curve” was established, moving memory from mystery to engineering.

Over time, SuperMemo’s early ideas spread widely, inspiring a generation of learning tools and helping shape the way the world thinks about memory, review, and long-term retention.

Decades of refinement led to SM-20, an algorithm that calculates the optimal moment for review with the highest recall probability.

Today, spaced repetition is used by hundreds of millions of people across major learning apps.

Now, for the first time, this technology is available as a ready-to-use API.

Spaced repetition is a learning method based on reviewing information at carefully timed intervals so you remember more and forget less. It did not appear out of nowhere as a trendy study hack.

Its modern form grew out of decades of memory research, but the breakthrough came with SuperMemo in the 1980s, when Piotr Woźniak began turning the problem of forgetting into a practical learning system.

With more than 30 years of history behind it, spaced repetition is still evolving, and the algorithm continues to be refined and improved. The story is fuller, more surprising, and far more nuanced than the simplified versions repeated online today. Read the full article and discover how spaced repetition really evolved: The True History of Spaced Repetition.

Not all spaced repetition algorithms are equal.

A good algorithm must accurately predict the probability that a learner will remember a given piece of information at a given time. Based on that prediction, the system can decide when the next review should happen – for example, when recall probability drops to 90%, which is the default target in SuperMemo.

This may sound simple, but high-quality recall prediction is difficult. It depends on probabilistic modelling, real-world repetition data, and long-term validation. That is exactly where SuperMemo stands apart.

SM-20 is the result of decades of research into memory optimization. It is designed not just to schedule reviews, but to do so with precision, efficiency, and personalization.