Spaced repetition schedule calculator
Pick the day you learned something. Get the days to review it so it sticks, and put them straight into your calendar.
Review what you learned 1 day later, then 3 days, 1 week, 3 weeks, 6 weeks and 3 months later. Before an exam, use shorter gaps and finish the day before. Each time, test yourself before you look at your notes.
- Day 1The day after you learned it+1 day
- Day 43 days after the last review+3 days
- Day 111 week after the last review+1 week
- Day 323 weeks after the last review+3 weeks
- Day 77About 6 weeks after the last review+45 days
- Day 167About 3 months after the last review+90 days
Your dates stay in your browser. "Add to calendar" downloads a standard .ics file that works with Apple Calendar, Google Calendar and Outlook, with a reminder at 9 am on each review day.
How the schedule works
Right after you learn something, it starts to fade, quickly at first and then more slowly. That is the forgetting curve. A review pulls the idea back out of memory just as it starts to slip, and every successful recall makes the next drop slower. So each gap can be longer than the last.
The calculator uses gaps of 1, 3, 7, 21, 45 and 90 days, each one about two to three times the previous. This is the same pattern behind SM-2, the algorithm many flashcard apps are built on, including Prismo: by default, each correct answer multiplies the interval by about 2.5.
| Review | Gap since the last one | Days after learning |
|---|---|---|
| 1st | 1 day | Day 1 |
| 2nd | 3 days | Day 4 |
| 3rd | 1 week | Day 11 |
| 4th | 3 weeks | Day 32 |
| 5th | About 6 weeks | Day 77 |
| 6th | About 3 months | Day 167 |
After the sixth review, most ideas will stay with you for a long time. Anything you still care about can come back once or twice a year.
Review schedules for an exam
When you have a deadline, the goal changes: you need the material at its strongest on one specific day. The calculator keeps the same expanding gaps, stops adding them once they would run past the exam, and always ends with a review the day before.
| Exam in | Review on these days after learning |
|---|---|
| 1 week | Day 1, 4 and 6 |
| 2 weeks | Day 1, 4 and 13 |
| 1 month | Day 1, 4, 11 and 29 |
| 2 months | Day 1, 4, 11, 32 and 59 |
| 6 months | Day 1, 4, 11, 32, 77 and 179 |
This matches what research on the spacing effect found. In a study of more than 1,300 people, Cepeda and colleagues tested gaps between study sessions of up to 3.5 months and final tests up to a year later. The best gap grew with the time until the test: around 20 to 40% of that time for a test one week away, falling to 5 to 10% for a test a year away. Short deadline, short gaps. Long deadline, longer gaps.
Learning something new the week before an exam? The schedule still helps, but there is less room for spacing to work. Start reviewing early in the course if you can.
What to do in each review
- Recall first, then look. Close your notes. Write down or say out loud everything you remember, or answer a few questions you wrote earlier. This is active recall, and it is what makes reviews work.
- Check and fix. Open your notes and compare. Fill in what you missed or got wrong. The gaps you notice are exactly what the next review will strengthen.
- Bring back what you missed sooner. If you could not recall an idea at all, review it again the next day, then continue the schedule from there.
- Keep it short. A review should take a few minutes, not an hour. Reading everything again feels thorough, but testing yourself does far more in less time.
Reviews work best on things you understood in the first place. If a topic still confuses you, spend the time understanding it before you start spacing it out. Our guide on how to remember what you read covers how to take notes that are easy to review.
By hand or with an app?
For one chapter or one course, a calendar works well: put the dates in, open your notes on each day, quiz yourself. It starts to break down once you are keeping many things at once. Ten books a year with a dozen ideas each is hundreds of reviews, every one on its own schedule, and every wrong answer should reset its own timer.
That is the job spaced repetition apps do. Anki schedules flashcards that you write yourself. Prismo, the app I make, starts from your notes instead: you write or dictate what you learned, it turns that into questions, and it schedules each one, adapting the gaps to your answers.
Sources
- Cepeda, N. J., Vul, E., Rohrer, D., Wixted, J. T., & Pashler, H. (2008). Spacing effects in learning: A temporal ridgeline of optimal retention. Psychological Science, 19(11), 1095–1102.
- Cepeda, N. J., Pashler, H., Vul, E., Wixted, J. T., & Rohrer, D. (2006). Distributed practice in verbal recall tasks: A review and quantitative synthesis. Psychological Bulletin, 132(3), 354–380.
- Karpicke, J. D., & Roediger, H. L. (2008). The critical importance of retrieval for learning. Science, 319(5865), 966–968.
- Wozniak, P. A. (1990). Optimization of learning. Master's thesis, University of Technology in Poznań. The origin of the SM-2 algorithm.
