Spaced Repetition Calculator

What Is Spaced Repetition?

Spaced repetition is a study technique that schedules reviews at increasing intervals. Instead of cramming everything in one session, you review each card right before you are likely to forget it. This approach is grounded in the forgetting curve discovered by Hermann Ebbinghaus in 1885, which shows that memories decay exponentially unless reinforced at the right moment.

Modern spaced repetition systems (SRS) like Anki use algorithms such as SM-2 to decide when to show each card again. After you first learn a card, you might see it again in 1 day, then 3 days, then 7 days, then 16 days, and so on. Each successful review roughly doubles the interval. A card you keep getting right might eventually be scheduled months or even a year into the future, while a card you struggle with stays in tight rotation.

How Spaced Repetition Intervals Work

A typical interval sequence looks something like this: a new card is first reviewed after 1 day, then after 3 days, 7 days, 15 days, 30 days, and eventually several months later. The exact schedule depends on your performance. If you answer correctly, the interval grows. If you get it wrong, the card resets to a shorter interval so you see it again sooner.

The key insight is that each review strengthens the memory trace by a greater amount than the previous one. Early reviews do the heavy lifting, and later reviews are quick refreshers that keep the memory alive with minimal effort. Over time, you spend less and less time on material you already know, freeing up study time for new cards.

Why Spaced Repetition Is the Most Effective Study Method

Decades of cognitive science research confirm that spaced repetition dramatically outperforms massed practice (cramming). Students who use SRS retain up to 90% or more of what they learn long-term, compared to roughly 20-30% retention after a single cram session. Medical students, language learners, and professionals use it to master thousands of facts in a fraction of the time traditional study would require.

The Ebbinghaus forgetting curve shows that without review, we lose about 50% of new information within an hour and up to 70% within 24 hours. Spaced repetition combats this by timing each review at the point of optimal difficulty, where recalling the answer takes effort but is still possible. This effortful retrieval is what strengthens the memory.

How to Use This Calculator

Enter the total number of flashcards you need to learn, pick your target retention rate (90% is the sweet spot for most learners), set how many days per week you can study, and choose your session length. The calculator uses an SM-2-based model to estimate how many new cards you can introduce each day, how your daily review load will grow over time, and how many weeks it will take to get through your entire deck.

Use the week-by-week schedule to see when your review load peaks and plan accordingly. If the load bar turns red, consider studying longer sessions, spreading reviews across more days, or lowering your target retention slightly.

Create Your Flashcards with Klarrity

Once you have a study plan, you need flashcards. Klarrity is a Chrome extension that turns any webpage into study-ready flashcards. Highlight text or capture images, and Klarrity generates question-answer cards using AI. Export directly to Anki, Quizlet, Notion, Obsidian, or CSV and start reviewing with the schedule this calculator builds for you.