Spaced Repetition
Spaced repetition is one of the most powerful, evidence-backed learning techniques ever discovered. By reviewing material just as you're about to forget it, you strengthen memory with remarkably little total effort. Here's how it works.
The forgetting curve
Memory decays predictably over time. Each well-timed review flattens the curve, making the next lapse slower and the memory more durable.
The Leitner system
This simple flashcard method sorts cards into boxes reviewed at increasing intervals. Our Flashcard Scheduler shows exactly when to review each box.
Combine with active recall
Spacing works best paired with active recall — retrieving the answer, not just seeing it.
Used consistently, spaced repetition lets you retain large amounts of information for months or years with just minutes of daily review.
The science behind spaced repetition
Spaced repetition is built on the forgetting curve, first described by Hermann Ebbinghaus in the 1880s, which shows that memory fades predictably over time unless it is reinforced. The clever insight is that each time you successfully recall a fact just before you would have forgotten it, the memory becomes more durable and the next review can be pushed further into the future. This is why a well-spaced review schedule lets you retain hundreds of facts with only a few minutes of daily practice, something that would be impossible with cramming.
How the Leitner system works
The Leitner system is a simple, paper-friendly way to apply spaced repetition using boxes. New and difficult cards live in the first box and are reviewed most often. Each time you answer a card correctly it moves to the next box and is reviewed less frequently; each time you miss it, it drops back to the first box. Over time, the cards you know drift into rarely-reviewed boxes while the cards you struggle with stay close and get more attention. Our flashcard scheduler implements this system for you so you never have to track boxes by hand.
Getting the most from your reviews
Spaced repetition only works if each review is a genuine act of recall, so always try to answer before flipping the card. Keep cards short and focused on a single fact, because long, compound cards are hard to grade honestly. Pair the method with our guide on active recall for the underlying technique, and review consistently, since a five-minute daily habit beats a two-hour weekend marathon every time.
The science of spacing
Spaced repetition is built on a well-documented feature of memory: we forget information along a predictable curve, but each review resets and flattens that curve. By revisiting material just as you are about to forget it, you strengthen the memory more efficiently than by cramming. Over several spaced reviews, the intervals can grow longer and longer while the knowledge becomes increasingly permanent, which is why spacing is so effective for long-term retention.
Putting spacing into practice
You do not need special software to benefit from spacing, though flashcard apps that schedule reviews for you make it effortless. The core habit is simply to review material at increasing intervals, perhaps a day later, then a few days, then a week, rather than in a single marathon session. Combining spaced repetition with active recall, by testing yourself at each interval, produces the strongest results, turning short study sessions into deep, lasting knowledge.
Frequently asked questions
How many new cards should I add per day? Start small, around ten to twenty, because every new card generates future reviews. Adding too many at once creates an overwhelming backlog within a week.
What if I miss a few days? Simply resume; do the overdue reviews and carry on. The schedule is forgiving, and a short break will not undo your progress.
Is spaced repetition good for understanding or just memorising? It excels at durable memory of facts, vocabulary, and formulas. Combine it with problem practice and explanation for deep conceptual understanding.