Knowledge Retention Estimator

The Ebbinghaus forgetting curve is a model discovered by German psychologist Hermann Ebbinghaus in 1885, replicated by Murre & Dros (2015, PLOS ONE). It describes how retention drops rapidly after learning: 58% retained at 20 minutes, 44% at 1 hour, 33% at 1 day, 25% at 1 week, and 21% at 1 month. The curve follows an exponential decay pattern.

Spaced repetition works by reviewing information at increasing intervals, which strengthens memory consolidation each time. The first review might happen after 1 day, the second after 3 days, the third after 7 days, and so on. Each review resets the forgetting curve to a higher baseline, so retention after 30 days with 3-4 spaced reviews can reach 85-95%, compared to 10-20% without any review.

According to the Ebbinghaus forgetting curve (replicated by Murre & Dros, 2015), retention drops to about 33% after 1 day, 25% after 1 week, and 21% after 1 month without reinforcement. The steepest drop happens in the first hour (to 44% retained). This means a one-time training session loses most of its value within days.

Research supports reviewing at 1 day, 3 days, 7 days, and 21 days after initial training for optimal long-term retention. Each review can be brief (5-10 minutes of key concepts). This schedule typically achieves 85-95% retention at 30 days.

Yes, but not linearly. Longer training sessions actually have diminishing returns for retention. A 1-hour focused session and a 4-hour session may produce similar retention at 30 days because attention and encoding capacity drop after 45-60 minutes. Breaking long training into shorter sessions with gaps between them (distributed practice) significantly outperforms massed practice.