Spaced Repetition Calculator
Plan a spaced repetition review schedule to maximize long-term retention of study material before a test.
Results
Visualization
How It Works
Spaced repetition is the most evidence-backed study technique in cognitive science. Instead of reviewing material once, you review it at increasing intervals (1 day, 3 days, 7 days, etc.). Each review takes less time but strengthens the memory trace, fighting the natural forgetting curve.
The Formula
Variables
- Forgetting Curve — Without review, you forget ~50% of new material within 24 hours and ~80% within a week
- Spacing Effect — Spacing reviews over time creates stronger, longer-lasting memories than massed practice
- Time Decay — Each review round takes less time (100%, 70%, 50%, 35%, 25%) as retrieval gets faster
Worked Example
10 topics, 21 days to test, 20 min per topic initially: You fit 4 review rounds (day 1, 3, 7, 14). First review: 200 min. Second: 140 min. Third: 100 min. Fourth: 70 min. Total: 8.5 hours spread over 3 weeks, averaging 24 minutes per day.
Practical Tips
- Start spaced repetition as early as possible — you need at least 1-2 weeks for the spacing intervals to work.
- Use active recall during each review: close your notes and try to write down everything you remember before checking.
- Flashcard apps like Anki automate spaced repetition scheduling, but you can also use a simple calendar.
- Each review session should focus on self-testing, not re-reading. Re-reading creates an illusion of knowledge without real retention.
- If you struggle with a topic during review, reset its interval — review it again the next day before extending the gap.
Frequently Asked Questions
How effective is spaced repetition compared to cramming?
Extremely effective. A meta-analysis by Cepeda et al. (2006) across 254 studies found that spaced practice produced significantly better long-term retention than massed practice (cramming), often by 30-50%. The advantage grows larger over longer retention periods.
Why do later reviews take less time?
Each successful retrieval strengthens the memory trace, making subsequent recall faster. The first review might take 20 minutes per topic because you are re-learning forgotten material. By the fourth review, you are reinforcing strong memories and only need to refresh weak spots.
What if I do not have enough days for all the intervals?
Use whatever time you have. Even 2 review rounds (day 1 and day 3) are significantly better than one review. The calculator automatically fits as many rounds as possible into your available time. Shorter intervals (1, 2, 4 days) still provide substantial benefit.
Should I review all topics in every session?
Ideally yes, but if time is limited, prioritize topics you found hardest during previous reviews. The whole point of spaced repetition is that well-remembered topics need less time, freeing you to focus on weaker areas.
Can I use spaced repetition for non-memorization subjects?
Absolutely. For problem-solving subjects (math, physics), re-do practice problems at spaced intervals without looking at solutions. For essay-based subjects, practice outlining arguments from memory. The principle of spaced retrieval applies to any type of knowledge.