German psychologist Hermann Ebbinghaus's research on memory led to the development of the "Forgetting Curve," which illustrates how information is lost over time when there's no attempt to retain it. His findings suggest that without reinforcement, we forget approximately 50% of new information within an hour, 70% within 24 hours, and up to 90% within a week. Spaced repetition counters this by scheduling reviews at optimal intervals, effectively combating the natural decline in memory retention.

A study by Cepeda et al. (2006) reviewed the effects of spaced repetition on memory retention. The research demonstrated that spaced repetition can lead to significant improvements in long-term recall compared to massed practice (cramming). Specifically, participants who engaged in spaced learning sessions showed up to double the retention rates of those who used traditional study methods.

Implementing spaced repetition techniques allows learners to reduce the time needed to memorize and retain information effectively. By revisiting material at strategically increasing intervals, the brain reinforces memory pathways more efficiently.This method can cut the required study time significantly — some reports suggest by up to 50% — while achieving the same or better retention outcomes compared to traditional study practices.

In a comprehensive review of learning techniques, Dunlosky et al. (2013) evaluated various study methods for their effectiveness. Spaced repetition was identified as one of the most effective strategies, receiving a high utility assessment. The technique's ability to enhance long-term retention and its applicability across different learning contexts underscore its efficiency and effectiveness.

The timing of reviews in spaced repetition is crucial. Research indicates that reviewing material just before it's likely to be forgotten significantly strengthens memory retention. This approach leverages the optimal moments when the memory trace is vulnerable, thereby enhancing the durability of the memory with each timely review.

High-achieving learners across various fields utilize spaced repetition systems (SRS) to manage and master large volumes of information. Medical students, for instance, often use tools like Anki to prepare for exams, benefiting from the method's efficiency in handling extensive medical knowledge. Similarly, language learners and memory competitors employ SRS to enhance vocabulary acquisition and memorize complex information, respectively.

Owl uses FSRS-5 (Free Spaced Repetition Scheduler), a sophisticated and modern open-source spaced repetition algorithm. FSRS-5 uses machine learning trained on over 100 million real review records to predict the optimal time for each review. Unlike older algorithms that use fixed intervals, FSRS-5 adapts to your personal learning patterns and the difficulty of each card. This means you'll spend less time reviewing and achieve better retention—the algorithm knows exactly when you need to review each card to maintain long-term memory.

Spaced repetition systems, such as Owl (that's us!), Anki and SuperMemo, are designed to optimize learning by scheduling reviews at increasing intervals tailored to the individual's forgetting curve. This personalized approach ensures that even with minimal daily time investment—sometimes as little as five minutes—learners can achieve long-term retention of vast amounts of information. The key lies in the strategic timing of reviews, which reinforces memory just as it's needed.