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: Spaced repetition yields exponential returns for small increases in effort.

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