Spaced repetition memory systems are extremely efficient

Using a Spaced repetition memory system, you can memorize the answers thousands of questions in just a few minutes a day. This is the unintuitive consequence of an exponential at work in the Spacing effect.

Each time you remember an answer correctly, that question’s test interval increases geometrically, forming an exponential curve: 5 days, 2 weeks, 1 month, 2 months, 4 months, etc. If you add questions at a constant rate, and each question’s probability of occurring on a given day diminishes exponential with time, then you’ll have a roughly constant number of questions to review on a given day.


Branwen, G. (2009). Spaced Repetition for Efficient Learning. Retrieved December 16, 2019, from

Nielsen, M. (2018). Augmenting Long-term Memory. Retrieved from