So you have learned that spaced repetition can help you to study effectively, but it is not clear what should be the intervals between your repetition sessions.
As a general rule, the material should be studied again once at least a bit of forgetting has set in (forgetting at least 10% of the material), but not too much (forgetting more than 50%) so as not to end up relearning material from scratch. For most this would mean the following intervals:
- 1 hour after the first learning or on your next study session
- 1 day after the previous learning
- 2 days after the previous learning
- 5 days after the previous learning
- 10 days after the previous learning
- 30 days after the previous learning or the day before the test
Of course, this topic is a bit more nuanced, there is no one perfect set of intervals that will fit everyone. The exact intervals will depend on your situation – so read on to learn more.
What are the optimal spaced repetition intervals based on existing spaced repetition algorithms?
A lot of the advice above is based on the existing spaced reception algorithms and the default intervals they have. See the table below for a summary of optimal spaced repetition intervals based on the common algorithms.
| SM-2 | Leitner system | FC-3 | Anki (approx.) | |
| Interval 1 | 1 day | 1 day | 31 minutes | 1 minute |
| Interval 2 | 6 days | 3 days | 12 hours | 10 minutes |
| Interval 3 | 15 days | 5 days | 1 day | 3 days |
| Interval 4 | 35 days | 30 days | 2 days | 9 days |
| Interval 5 | 82 days | 30 days | 5 days | 12 days |
| Interval 6 | 189 days | 30 days | 10 days | 45 days |
| Interval 7 | 391 days | 30 days | 23 days | 102 days |
Of course, it is important to note that the above intervals only apply if you do not make a mistake and recall the information mostly correctly in each of your study sessions. If you make a mistake most of these algorithms will make you start from the beginning.
For example, if you make a mistake on interval 3 while using the Leitner system, your intervals would reset, and the next interval would be in 1 day’s time.
| SM-2 | Leitner system | FC-3 | Anki (approx.) | |
| Next interval if you make a mistake | 1 day | 1 day | 31 minutes | 1 min |
| 2 interval after a mistake | 6 days | 3 days | 32 minutes | 10 min |
| 3 interval after mistake | 15 days | 5 days | 13 hours | 4 days |
| 4 interval after a mistake | 35 days | 30 days | 1 day | 9 days |
| 5 interval after a mistake | 82 days | 30 days | 2 days | 20 days |
If you review all of these intervals you could see that most of them are relatively similar with just small differences. Furthermore, if you add in practical considerations such as that most of us generally have up to 2-3 study sessions per day you can summarize the recommended intervals in the following way:
- 1 hour after the first learning or on your next study session
- 1 day after the previous learning
- 2 days after the previous learning
- 5 days after the previous learning
- 10 days after the previous learning
- 30 days after the previous learning or the day before the test
And if you make a major mistake – reset the intervals for that specific piece of knowledge or flashcard.
Lastly, you should repeat something when at least a little of forgetting as set in. A general rule of thumb is that it makes sense to repeat the information if you forgot about 20% of it.
What’s the best spaced repetition schedule?
There is no one best-spaced repetition schedule that will work for everyone since the exact time of each repetition depends on how much you have forgotten. And that depends on numerous factors such as:
- how difficult the information is
- how easy it is to learn based on your existing knowledge
- how easy it is to learn based on your learning skills & methods
- etc.
According to, Piotr Woźniak, a pioneer in memory research, the optimal intervals are ones that:
- Are short enough to ensure that you still remember something
- Not too often so as to not spend time inefficiently
“Intervals should be as long as it is necessary for a selected small proportion of knowledge be forgotten.”
Piotr Woźniak
Such logic is in line with what leading scientists, Brown, Roediger, and McDaniel, recommend in their book, Make it Stick:
“How big an interval, you ask? The simple answer: enough so that practice doesn’t become a mindless repetition. At a minimum, enough time so that a little forgetting has set in… Sleep seems to play a large role in memory consolidation, so practice with at least a day in between sessions is good.”
Make it Stick, Brown, Roediger, and McDaniel
So the challenge is that the best-spaced repetition schedule is unique to everyone and should be adapted based on your situation.
Solution 1 – flashcard apps
A simple solution to this issue is to use a flashcard app like Anki that has a built-in spaced repetition algorithm that will monitor how well you remember each card and will automatically show you the cards so that you would be studying them in an efficient way.
While flashcards are an efficient way of learning and not having to worry about making your own spaced repetition schedule – what if you do not want to use these apps?
Solution 2 – the Leitner system
You can always make your own flashcards (or some other units of knowledge) and then space out your learning and adjust the intervals if you get a card wrong. A simple and intuitive way of doing so is to use the Leitner system.
The idea behind the Leitner system is simple – you just need to categorize all your flashcards into 5 boxes (if you want you can have more or less than 5 boxes), where each category stands for a different study interval. All of your cards will initially start in the first box.
Every time you get a card right, you should put it in the next box in line. And every time you get a card wrong it should go to box 1, regardless of in which box it was before. For example, even if a card was in box 4 if you got it wrong it should go back to box 1.
There are many ways of structuring the intervals for boxes and you could experiment with what works best for you. But based on the existing spaced-repetition algorithms we recommend the following intervals for the boxes
- Box one – review daily
- Box two – review every other day
- Box three – review once per week
- Box four – review once every 2 weeks
- Box five – review once per month or the day before the test
But what if you do not want to use flashcards or you want to create your own system instead?
How do you make a spaced repetition timetable?
One of the best methods and the one that I use is to use google sheets or notion and make a table where each line stands for a certain topic or sub-topic that you are learning (it is primarilly based on Ali Abdaal spaced reptition table). You want to make sure that each line or each knowledge unit in that table is:
- not too large (e.g. larger than 1000 words) as it might be too overwhelming
- cohesive – represents a single concept or idea
For example, you could make the following table:
Each topic can be then further grouped into parent topics and subjects. For example, I grouped integrals and derivatives fundamentals under advanced math, and then further grouped advanced and basic math parent topics under the math subject.
Once you make your table after each study session mark the date when you studied and use a color or an emoji to mark how well did you do – did you recall everything very well (green emoji 🟢), did you struggle a bit (yellow emoji 🟡), or did very poorly (red emoji🔴 )?
Depending on how you did you should plan your next session. If you did bad then your next session should be the next day, if you did well, then you can push your next study session for this topic to a later time.
But you might ask – how to plan out your study sessions in advance? Well, we recommend using the following intervals, and if you make a major mistake in any of your study sessions then reset the intervals for that subject.
- 1 hour after the first learning or on your next study session
- 1 day after the previous learning
- 2 days after the previous learning
- 5 days after the previous learning
- 10 days after the previous learning
- 30 days after the previous learning or the day before the test
For example, if you study fundamentals of integrals on the 11th May morning, then your next study sessions could be:
- 11th of May evening
- 12th of May
- 14 of May
- 19 of May
- 29 of May
- 28 of June
And if you make a mistake one of these sessions then the intervals for that topic reset:
- 11th of May evening
- 12th of May
- 13 of May morning (🔴 made a major mistake)
- 13 of May evening
- 14 of May
- 15 of May
- etc.
Of course, you should treat these suggestions just as a set of rough guidelines. You might not always be able to study the topic twice a day or you might have some sort of a commitment and might have to push your study session to another day. Or you might want to push some sessions closer because the exam is sooner and you feel weak in some topics.
Furthermore, what many of the spaced repetition guides miss, is that you should consider how important the topic is. You might not always have the time to go through all of the topics you have planned out – so you should prioritize the ones that are the most relevant and will give you the most points in the exam or test.
So in summary, you will be fine as long as you follow these general principles:
- List out all of your topics and group them
- Plan out your study sessions based on the suggested intervals
- Mark down the real-time of each study session and how well you did
- Based on how well you remember each topic and how important it is, adjust your schedule:
- The stronger you feel about a topic the farther the next learning interval should be
- The weaker you feel about a topic the closer the next interval should be
- The less important the topic is the farther the next interval should be
- The more important the topic is the closer the next interval should be
As long as you stick to these general principles you are fine, you do not need a fancy table or some magic app or algorithms. For example, Ali Abdaal, a successful student at Cambridge University, used this basic google sheet to track and plan his spaced reptition sessions (see picture below).
Free spaced repetition table templates
Hope the guide above was helpful.
My notion spaced repetition table -> get it here
My google sheets spaced repetition table -> get it here
Both of these templates have a spaced repetition calculator that will calculate all of the upcoming study sessions based on the proposed intervals above.
However, I generally do not use this calculator since the math behind the intervals is relatively easy and you can just do it in your head – you do not need to be super accurate after all.
Also, a small note – I personally use the notion spaced repetition table, since each line is a notion page in which I can write all of the questions and other info on which I want to test myself.
There are other templates that you could use as well (see them below) although I have to admit that I do not like them that much, since they involve various formulas and are rather complicated. What is important is that (as I mentioned before) you would use the key principles that I described above.
Spaced repetition table template by Red Gregory -> get it here
Spaced repetition table template by Connor Dibblin -> get it here
Spaced repetition table template based on Ali Abdaal’s video -> get it here