The spaced repetition calculator uses the Ebbinghaus forgetting curve to generate optimal review intervals. Review too soon and you waste time; review too late and you've already forgotten. This tool finds the exact right moment.
Calculator Settings
80-90% is optimal. Higher = more frequent reviews.
Flashcards, vocabulary words, formulas, etc.
Review Intervals
Click "Calculate" to see your schedule
Forgetting Curve Visualization
Retention over 90 days — each review resets the curve at a higher baseline
Daily Review Load Projection
Estimated reviews per day as your deck grows
How Spaced Repetition Works
Spaced repetition is one of the most evidence-backed learning techniques ever studied. By reviewing material at precisely the right intervals — just before you're about to forget — you spend less total time studying while retaining far more long-term.
The Forgetting Curve Formula
Hermann Ebbinghaus discovered that memory decays exponentially: R = e^(-t/S), where R is retention (0-1), t is time since last review, and S is memory stability. Each review increases S, meaning the curve decays more slowly after each successful review.
How to Use the Calculator
Set your target retention rate (85% is a good default), choose how deeply you initially learned the material, and enter how many items you need to memorize. The calculator outputs the optimal days to review — reviewing on day 1, 3, 7, 14, 30, and 60 is a common starter schedule. As memory stability grows, reviews become less frequent.
Managing Your Daily Review Load
The daily review load projection shows how your review burden grows as you add new cards. With 10 new cards per day, you'll have about 10 reviews in Week 1, growing to 50-80 by Month 1, and plateauing around 100-150 after Month 3. If the load feels too high, reduce your new-cards-per-day setting or accept a slightly lower retention target.
Practical Tips
Use an app like Anki to automate your spaced repetition schedule — doing it manually is only feasible for small decks. Focus on quality over quantity: 20 cards deeply understood beats 100 cards skimmed. The spaced repetition calculator is most powerful for vocabulary acquisition, medical terminology, formulas, and any recall-based learning.
FAQ
Is the Spaced Repetition Calculator free?
Yes, completely free with no signup required. All calculations run locally in your browser.
What is spaced repetition?
Spaced repetition is a learning technique that schedules review sessions at increasing intervals. Instead of reviewing flashcards every day, you review them on day 1, day 3, day 7, day 14, and so on. Each successful review resets the forgetting curve at a higher baseline.
What is the Ebbinghaus forgetting curve?
Hermann Ebbinghaus discovered in the 1880s that memory decays exponentially over time. His formula: retention = e^(-t/S), where t is time elapsed and S is memory stability (which increases with each review). Without review, you forget roughly 70% of new information within 24 hours.
What retention rate should I target?
80-85% is a common target that balances review frequency with long-term retention. Higher targets (90-95%) require more frequent reviews, which can feel unsustainable. Anki's default is 90% retention.
How does learning strength affect intervals?
Strong initial learning (deep understanding, not rote memorization) creates higher initial memory stability. This means you can wait longer before your first review. Weak learning requires reviewing sooner to prevent forgetting.
Why does daily review load grow over time?
As you add new items to your deck, old items mature into longer intervals while new items need frequent review. The daily load grows for the first 2-3 months before plateauing, because mature cards need only monthly reviews while you keep adding new cards daily.
What tools use spaced repetition?
Anki is the most popular free flashcard app using spaced repetition. Others include Quizlet (partial), Duolingo, Memrise, and SuperMemo (the original commercial app). The intervals our calculator generates closely match Anki's SM-2 algorithm.