# FAQ: Spaced Repetition — Everything You Need to Know About the Most Effective Memorization Method
Spaced repetition is a learning technique that involves reviewing information at increasing time intervals, calibrated to intercept forgetting just before it happens. This is not a productivity hack or a pedagogical gimmick. It is the result of over 130 years of research in cognitive psychology, from Hermann Ebbinghaus's foundational work in 1885 to the modern meta-analyses by Cepeda et al. (2006) and Dunlosky et al. (2013). Spaced repetition is rated among the only two "highly effective" study techniques by research. This guide answers the 15 most common questions about this method, with concrete, science-based answers you can apply to your studies right away.
What is spaced repetition, in two sentences?
Spaced repetition means reviewing information not in a loop on the same day, but at precise moments over time: for example at D+1, D+3, D+7, then D+21. Each review strengthens the memory trace and pushes back the moment you would have forgotten. The principle relies on a well-documented phenomenon: when you retrieve information just before forgetting it, your brain consolidates it more deeply than if you re-read it while you still remember (Bjork & Bjork, 1992). This is what researchers call "desirable difficulties": a slightly challenging retrieval effort produces stronger learning than an easy one. This is counterintuitive, because we feel like we learn better when everything flows smoothly. But fluency is often an illusion of mastery. Learn more about spaced repetition.
What is Ebbinghaus's forgetting curve?
In 1885, German psychologist Hermann Ebbinghaus conducted a series of memorization experiments on himself using meaningless syllables. He measured how long he retained these syllables and plotted what we now call the forgetting curve. The result: without review, you lose about 50% of new information within 20 minutes, 70% within 24 hours, and over 90% within a week. This curve has been confirmed by dozens of subsequent studies. But Ebbinghaus also showed that each review "flattens" the curve: after a retrieval, the forgetting slope becomes less steep, and the information stays accessible longer. Spaced repetition exploits exactly this mechanism. You are not reviewing for the sake of re-reading. You are reviewing at the precise moment when the curve threatens to tip into forgetting.
What are the optimal review intervals?
The research by Cepeda et al. (2006) analyzed 254 studies on distributed practice and concluded that there is no single optimal interval: the best spacing depends on the gap between your last review and the final test. For an exam in one month, short intervals at the start (D+1, D+3) followed by increasingly longer ones (D+7, D+14) work well. For very long-term retention, Pashler et al. (2007) showed that the optimal interval between the first and second review is roughly 10 to 20% of the delay before the test. If your exam is in 60 days, your first review should happen 6 to 12 days after initial learning. In practice, most spaced repetition algorithms (SM-2, FSRS) calculate these intervals automatically. You do not need to plan manually. Discover study methods that actually work.
What is the difference between spaced repetition and rote learning?
Rote learning, in everyday terms, means repeating information in a loop until it "sticks." Researchers call this massed practice. You re-read the same notes ten times in one evening. The problem is that it works... in the short term. You pass the next-day quiz, then forget everything within two weeks. Spaced repetition also uses repetition, but distributes it strategically over time. The fundamental difference is the timing of each repetition. In massed practice, you repeat while you still know. In spaced repetition, you repeat when you are starting to forget. Cepeda et al. (2006) demonstrated that distributed practice produces up to 150% more retention than massed practice, for the same total study time. It is not about working harder. It is about working at the right moment.
How do you use flashcards with spaced repetition?
Flashcards are the most natural medium for spaced repetition because they combine two powerful mechanisms: active recall and spacing. A good flashcard poses a question on the front and waits for you to formulate your answer before checking on the back. This active retrieval process strengthens memory far more than passive re-reading (Karpicke & Roediger, 2006). For this to work, follow three rules. First, one idea per card: no lists of five points, no paragraphs. Second, make your question precise. Third, use an SRS (Spaced Repetition System) that automatically schedules reviews based on your performance. Wizidoo generates flashcards and quizzes directly from your course materials (photo, PDF, text) and handles the spacing automatically. AI flashcards vs. manual: the comparison.
What is the Leitner system?
The Leitner system, invented by German science journalist Sebastian Leitner in the 1970s, is a simple method for organizing spaced repetition with physical boxes. You place your flashcards in box 1. When you answer correctly, the card moves to box 2. If you get it wrong, it goes back to box 1. Box 1 is reviewed every day, box 2 every three days, box 3 once a week, and so on. The advantage of Leitner: it is tangible, and you can physically see your progress. The disadvantage: it is rigid. The intervals are fixed and do not adapt to the actual difficulty of each card. Modern algorithms like SM-2 and FSRS have replaced this logic with adaptive calculations. But if you are just starting out and prefer paper, Leitner remains an excellent first step toward spaced repetition.
What is the SM-2 algorithm?
SM-2 (SuperMemo Algorithm 2) is the spaced repetition algorithm created by Piotr Wozniak in 1987, originally for the SuperMemo software. It is the algorithm that popularized digital spaced repetition, and it is the one Anki uses as its foundation. How it works: each card has an ease factor that starts at 2.5. After each review, you assign a grade from 0 to 5 based on your mastery. If the grade is good, the interval is multiplied by the ease factor and the next review is pushed further out. If the grade is poor, the card returns to a short interval. The ease factor adjusts over time: a card you find difficult will have a lower factor and come back more often. SM-2 is elegant in its simplicity, but it has limits: it does not account for response time or your overall performance history. More recent algorithms (FSRS, the one used by Wizidoo) integrate this data for finer spacing.
Anki vs Wizidoo: which app should you choose?
Anki is an open-source tool, free on desktop and Android, paid on iOS. Its strength: total flexibility. You can create decks, customize SM-2 parameters, install add-ons, and share community-made decks. Its weakness: the learning curve is steep. The interface is austere, manual configuration is complex, and creating good flashcards takes time. Wizidoo takes the opposite approach: you import your course materials (photo, PDF, text), the AI generates tailored quizzes and flashcards, and the algorithm handles all the spacing with zero configuration. It is an app designed for students who want to start learning now, not spend an hour setting up a tool. If you are tech-savvy and want total control, Anki is solid. If you want immediate efficiency from your own courses, Wizidoo is built for you. Full Anki vs Wizidoo comparison.
What type of content works best with spaced repetition?
Spaced repetition is devastatingly effective for anything involving factual memorization: vocabulary, dates, formulas, definitions, anatomy, law, pharmacology, programming syntax. Kornell (2009) showed that spacing improves retention even for visual content like recognizing artistic styles. But the method is not limited to isolated facts. You can also use it for abstract concepts, as long as you formulate your questions correctly. Instead of "What is mitosis?", try "What is the key difference between mitosis and meiosis in terms of daughter cell count?": a question that forces comparison and reflection. What works less well: complex procedural skills (writing an essay, solving a novel math problem). For those, spaced repetition is a complement, not a replacement. You memorize the building blocks, then practice assembling them. How to use AI effectively for studying.
How much time per day should you spend on spaced repetition?
Good news: spaced repetition is designed to be short. That is the whole point. A daily session of 15 to 30 minutes is enough to maintain a large volume of cards in active memory. Kornell (2009) showed that short, frequent sessions produce better results than long, infrequent ones. The trap to avoid: adding too many new cards at once. If you add 50 cards per day, you quickly end up with 200 daily reviews, and the workload becomes discouraging. Start with 10 to 20 new cards per day maximum. Reviews of older cards will build up gradually. With Wizidoo, you do not have to manage this balance manually: the app calibrates the question flow based on your pace and progress. Strategies for acing your university exams.
How long before you see results?
The first measurable effects appear within the first week. Roediger and Karpicke (2006) showed that a single retrieval test after initial learning improves retention by 44% one week later compared to simple re-reading. So the moment you start testing yourself with spaced flashcards, you are already retaining more. Results on an actual exam, however, depend on your starting point and the volume of material to cover. A student who adopts spaced repetition one month before exams can see grades rise by one to two points on average, provided they work consistently. After three months of use, the difference becomes striking: you spend less time studying but retain more. The key is consistency. Ten minutes per day for 30 days beats three hours in a single evening. How to know if you are ready for your exam.
Does spaced repetition work for all subjects?
Dunlosky et al. (2013) reviewed hundreds of studies and concluded that distributed practice (including spaced repetition) works for "nearly all types of material and all age groups tested." This includes science, languages, history, law, medicine, music, and even motor learning under certain conditions. Some subjects benefit more: those that rely on a large volume of facts to retain (medicine, languages, biology) see the most dramatic gains. For more analytical subjects (mathematics, philosophy), spaced repetition serves to anchor fundamentals (theorems, key concepts, definitions), but it must be complemented with active problem-solving practice. The method is not a replacement for understanding. It ensures that what you have understood remains accessible when you need it. Active recall as an essential complement.
How do you start spaced repetition right now?
Three steps, no more. First, pick one chapter from a course you need to know for your next exam. Second, create flashcards (or let Wizidoo generate them automatically from a photo or PDF of your notes). Third, do your first review session and let the algorithm schedule the follow-ups. That is it. You do not need to understand the theory in depth or configure anything. The most common mistake beginners make is wanting to prepare everything before starting: building the perfect deck, finding the right tool, reading three more articles. Start with 10 cards. Do your first session. Add 10 cards tomorrow. Research by Karpicke and Roediger (2006) shows that simply testing yourself once outperforms three re-readings. The first step is the most valuable one. Try Wizidoo now.
Does it work if my exams are in 2 weeks?
Two weeks is tight, but it is enough for spaced repetition to make a difference. You will not have time to build very long-term memory (that takes months), but you can use compressed intervals: D+1, D+3, D+7, D+12. Pashler et al. (2007) showed that even short spacings (a few days) produce a significant advantage over massed practice. The two-week strategy: focus on the 20% of content that covers 80% of the exam. Generate your flashcards on day 1, do your first review on day 2, and let the algorithm guide you. Combine with intensive active recall: quizzes, past paper questions, verbal recall. You will not retain everything, but you will retain far more than by passively re-reading your notes. Tips for last-minute bac revision.
Does spaced repetition replace other study methods?
No. Spaced repetition is the best tool for long-term retention, but it does not cover the full spectrum of learning. It will not teach you to write an essay, solve a novel physics problem, or structure a legal argument. For those skills, you need deliberate practice: doing exercises, writing, training with past papers under real conditions. The optimal approach combines three pillars: initial understanding (reading, listening, comprehending), durable memorization (spaced repetition and active recall), and application (exercises, simulations, past papers). Bjork and Bjork (1992) describe "desirable difficulties": varying methods, interleaving subjects, and spacing reviews are complementary strategies that reinforce learning. Spaced repetition is the central pillar, but a pillar alone does not make a building. Study methods that truly work.
Take action
You now have answers to the 15 essential questions about spaced repetition. The science has been clear since Ebbinghaus: spacing your reviews and actively testing yourself are the two most powerful levers for lasting memorization. The rest is execution.
Wizidoo turns your course materials into quizzes and flashcards in seconds, with a built-in spaced repetition algorithm. Import a photo, PDF, or text, and start learning immediately.
Try Wizidoo for free — available on the App Store.
References
- Ebbinghaus, H. (1885). Über das Gedächtnis: Untersuchungen zur experimentellen Psychologie. Leipzig: Duncker & Humblot.
- Cepeda, N. J., Pashler, H., Vul, E., Wixted, J. T., & Rohrer, D. (2006). Distributed practice in verbal recall tasks. Review of General Psychology, 10(4), 354-380.
- Pashler, H., Rohrer, D., Cepeda, N. J., & Carpenter, S. K. (2007). Enhancing learning and retarding forgetting: Choices and consequences. Psychonomic Bulletin & Review, 14(2), 187-193.
- Roediger, H. L., & Karpicke, J. D. (2006). Test-enhanced learning: Taking memory tests improves long-term retention. Psychological Science, 17(3), 249-255.
- Dunlosky, J., Rawson, K. A., Marsh, E. J., Nathan, M. J., & Willingham, D. T. (2013). Improving students' learning with effective learning techniques. Psychological Science in the Public Interest, 14(1), 4-58.
- Karpicke, J. D., & Roediger, H. L. (2006). Is expanding retrieval a superior method for learning text materials? Memory & Cognition, 34(1), 151-163.
- Kornell, N. (2009). Optimising learning using flashcards: Spacing is more effective than cramming. Applied Cognitive Psychology, 23(9), 1297-1317.
- Bjork, R. A., & Bjork, E. L. (1992). A new theory of disuse and an old theory of stimulus fluctuation. In A. Healy, S. Kosslyn, & R. Shiffrin (Eds.), From Learning Processes to Cognitive Processes: Essays in Honor of William K. Estes (Vol. 2, pp. 35-67).