Spaced Repetition: A Guide to the Technique

Maximize the potential of your brain by using the spaced repetition memory technique in your studies.

“With frequent repetition, the capacity of consciousness may be increased.”

Hermann Ebbinghaus

Spaced repetition is a powerful technique that will help you memorize information in much less time than it would take otherwise. The idea of spaced repetition is to space out your repetitions, or review sessions, so that you are not trying to cram all the knowledge into your brain at once.

It’s not necessary, or practical, to try to memorize everything within a single session. Even though our brains are technically not muscles, they should still be treated as such.

Studying a textbook is like exercising your brain. But, the only difference is that when we study, we tend to try to cram all of our studying into one day instead of spacing it out over time. Thus, doing an all-nighter study session the day before an exam is essentially the same as trying to run thousands of miles the day before a marathon. It simply doesn’t work.

By cramming, all you’ll do is make your brain tired and lose whatever memories you did manage to build up. The memories in your brain become stronger through repeated, spaced study sessions, and that is what spaced repetition is all about.

This article will teach you how to use spaced repetition for studying and how to get the most out of this powerful memory technique.

In this guide, you’ll learn:

What is spaced repetition?

Spaced repetition is a memory technique that involves reviewing and recalling information at optimal spacing intervals until the information is learned at a sufficient level. This technique helps your brain remember more information as it keeps the material fresh in your mind and forces you to use active recall. Spaced repetition can be applied to any form of education from grade school math problems all the way up to graduate computer algorithms.

Spaced repetition is extremely effective in improving long-term memory recall when compared to other study methods such as rote learning and cramming before exams (repetition without spacing). It also increases the chance of an individual acquiring knowledge that is transferable to other contexts, and it reduces the overall amount of time spent on study sessions.

This is why the spaced repetition learning technique is so attractive to educators and parents. It cuts down on the time spent on studying while boosting the brain’s capabilities in retaining memories.

The technique is simple in theory but can be difficult to execute because most people tend towards impatience when trying to memorize something new or unfamiliar. As is the case with all study skills, there is a learning curve to spaced repetition, but it’s a curve that can be overcome. Doing so requires both discipline and intentionality, but those who do manage to execute the technique effectively can reap massive benefits.

What are the benefits of learning with the spaced repetition system?

There are many benefits to using spaced repetition and there many different applications of the system. An overarching benefit of the technique, though, is that it simply helps you memorize better. Improving your memory should be your #1 goal when applying the technique as that is what the method truly excels at.

Besides improving memory, These are some of the biggest benefits of spaced repetition:

  • Continually re-exposes you to information at spaced intervals.
  • Helps your brain build memories that have high levels of storage strength.
  • Increases the time spent actively rehearsing a memory in your brain rather than passively consuming information.
  • Allows for consolidation of new information with old related knowledge that has already been stored in long-term memory, making it easier to retrieve and recall the information at later dates.
  • Having a predictable spaced repetition schedule teaches your brain to predict when it will next see the material and respond with greater alertness and attention, making it easier for information in that time frame to be encoded into long-term memory.
  • The technique allows you to break up larger tasks into smaller chunks of work spaced at intervals throughout the day (e.g., break one chapter into three sections): an approach called chunking.

Spaced repetition and the Ebbinghaus forgetting curve

The Ebbinghaus forgetting curve is a graph that represents the way information is forgotten over time. This forgetting curve starts with near-perfect recall in the beginning, but as a person continues to forget the material, the curve flattens until the bottom line where the person can’t remember anything at all about what was studied.

Ebbinghaus forgetting curve
Ebbinghaus forgetting curve

Spaced repetition used the Ebbinghaus forgetting curve to its advantage by recalling information at strategic times and not letting the curve reach the bottom. The method forces you to review the information before your brain has a chance to forget all information due to the forgetting curve.

What’s important here, though, is that our memory becomes stronger when we revisit information after forgetting some of it: a concept called the “theory of disuse“. This means that not only do we avoid losing the information by using spaced repetition, but we also strengthen these memories by letting ourselves partially forget the information and then strengthening it again using recall.

Best spaced repetition algorithms and time intervals

The question of what are the optimal time intervals for spaced repetition has been studied for decades. While there is no clear answer to this day, there is no shortage of proposed algorithms. These algorithms tend to have different goals, but they all unite in their mission to calculate the most optimal intervals for maximizing the benefits of the spacing effect.

Here are four popular examples of spaced repetition algorithms:

SuperMemo

The SuperMemo spaced repetition algorithms are some of the most famous in the world. These algorithms have been in continuous development and optimization since 1982 when Dr. Piotr Wozniak from Poland developed his first SuperMemo algorithm for the DOS – the SM-0. Piotr Wozniak is a well-respected authority in the spaced repetition sphere, named “the inventor of a technique to turn people into geniuses” by Wired magazine in 2008.

Throughout the years, Piotr Wozniak has invested a lot of his time and energy into optimizing his SuperMemo spaced repetition algorithms. Perhaps the most famous version of the SuperMemo algorithm was the SM-2, developed by Wozniak in the late 1980s. The SM-2 is likely best known for being the spaced repetition algorithm that the open-source Anki software is based on. As of the writing of this article, the latest SuperMemo algorithm is the SM-18, released in 2019. However, the algorithm requires licensing, and you can only access it by buying yourself a license (or taking one of the SuperMemo language learning courses).

Some of the benefits of the SuperMemo spaced repetition algorithms include its ability to provide accurate difficulty estimations for flashcards and the algorithms’ ability to adapt to the learner, based on the individuality of their brain and memory. For power learners, the SM series of spaced repetition algorithms appears very promising, but their usage remains limited due to licensing requirements and an aging user interface. That is why learning with alternatives such as Anki makes sense to students who don’t want to pay for licensing.

Anki

Anki is one of the most popular flashcard-based spaced repetition systems in the world. Based on the original SM-2 algorithm from Piotr Wozniak, the Anki algorithm is an open-source system that can be used for free by all students (except for the Anki iOS app which costs $24.99).

The Anki system is becoming increasingly popular among medical students, language learners, and other types of students who need to memorize large quantities of facts and principles. The system is also beneficial for those who like to review their flashcards on a mobile device as the Anki app is available for both iOS and Android devices. Anki also allows you to create custom flashcards with custom scheduling, which is useful when you want to customize your calendar based on upcoming test dates and free time. Perhaps the most important thing to note about Anki, though, is its shareability.

By that, I’m referring to being able to easily share Anki decks online. Due to the widespread use of Anki, you can find an optimized deck on just about any topic. There’s the Pepper deck, Lightyear deck, UWorld deck, and many, many more. When it comes to the widespread availability of flashcard decks to choose from, there really is no alternative to the Anki community. While the Anki algorithms may not be as fine-tuned and optimized as the SM-series of algorithms, the user-friendliness and choice of decks still make Anki a very appealing choice.

Leitner System

The Leitner System is one of the earliest rehearsal algorithms that involves reviewing study materials (flashcards) at fixed spacing intervals. The algorithm was developed by Sebastian Leitner, a German science journalist in 1972 and it’s commonly used to this day due to its simplicity and effectiveness.

Some learners, however, consider the Leitner System outdated due to the existence of more modern algorithms such as SuperMemo and Anki. The original Leitner System only uses three boxes with fixed intervals, while modern spaced repetition algorithms offer more features that are more customizable depending on your needs as a learner.

Despite that, though, if you’re a learner that enjoys the act of writing flashcards by hand and feeling the physical touch of your flashcards, the Leitner System offers an excellent spaced repetition algorithm to get started.

Half-Life Regression

Half-life regression (HLR) is a new spaced repetition algorithm developed by researchers from the Duolingo language learning website and app. Backed by data from the 40+ million monthly active users of Duolingo, the half-life regression model was created to boost retention, increase student recall rates, and enhance learner engagement. Duolingo is great for picking up a second or third language within a convenient software package.

However, due to its lack of customization and the inability to create your own flashcards, it’s not exactly a competitor to open-source spaced repetition software such as Anki. The research that Duolingo did to develop this model became a published paper and further explanations on its effectiveness can be read there. For the purposes of language learning, though, Duolingo’s algorithms are certainly worth checking out.

How to use spaced repetition to study

In theory, spaced repetition is a simple concept. However, in practice, spaced repetition is not always as easy to follow through with. You need to take care of a few things for spaced repetition to be effective. For one, the intervals between repetitions must remain consistent (this does not mean fixed), even if it feels like there isn’t any progress being made at first. And, you have to make sure to take the time to create an efficient study session structure for yourself, whether that’s based on flashcards or something else. Keep in mind that the goal of using spaced repetition is to build up knowledge over time. Efficient learning takes time!

These are the four steps you need to take to use spaced repetition:

  1. Plan the spacing intervals of your study sessions.
  2. Review and study the information for the first time.
  3. Recall the information at the first spacing interval.
  4. Keep recalling the information at chosen spacing intervals.

Step 1: Plan the spacing intervals of your study sessions.

The first step of using spaced repetition is planning the spacing of your study sessions. This is perhaps the most important step of the entire process because it will serve as the foundation for your study system.

The optimal intervals depend on many factors, such as:

  • Complexity of the topic.
  • Scale of the topic.
  • Your learning capacity.
  • Any pre-existing knowledge on the topic.

All these factors will have an influence on how you should plan your spaced repetition study sessions. Thus, there’s no single “magic formula” to choosing the spacing of your study sessions.

However, one of the most commons ways of choosing spacing intervals involves doubling the spacing after every interval. At its most basic, it’s the algorithm that SuperMemo uses and it involves these repetitions:

Day 1 (Repetition 1) > Day 7 (Repetition 2) > Day 16 (Repetition 3) > Day 35 (Repetition 4)

This system provides a basic outline for remembering information without overloading your brain with new information too often. Try experimenting with different intervals to see what works the best for you.

Step 2: Review and study the information for the first time.

The second step of spaced repetition is to review and study your learning materials for the first time. To do this, make sure to set aside enough time and comfortable study space to fully cover the topic without distraction.

Studying the material for the first time includes going through your highlights, questions, or areas that need more attention, as well as reading any supplementary materials suggested by your instructor. When reviewing your materials for the first time, make sure to take your time – this will save you time in upcoming repetitions.

This is one of the hardest and most time-consuming steps of the spaced repetition method, but try not to worry if it’s difficult now. After doing this once, you’ll have an easier time recalling concepts during subsequent repetitions.

Step 3: Recall the information at the first spacing interval.

Now that you have studied and reviewed the concepts for the first time, it’s time to start using repetition. When repeating the materials for the first time, try to follow the same steps you followed for studying and reviewing. This will help you strengthen the pre-existing memories you acquired during step two rather than forming new memories (which is a more time-consuming and cognitively demanding process).

The first study session should be shorter than subsequent sessions so that more of one’s effort will go towards recalling information rather than learning new material. This also ensures that the following repetitions will have fresher content in which they can build off of each other without interference from previously learned concepts (as memory fades over time).

Step 4: Keep recalling the information at chosen spacing intervals.

Having finished your first repetition, all you need to do now is to keep going through the same learning process by recalling the same information at optimal intervals. When going through each cycle of spaced repetition, it is important to keep in mind that the intervals should be spaced out so as not to overwhelm your memory and make it difficult for you to recall what has been learned.

Stick to the schedule you chose in step #1 and have trust in your system. Spaced repetition takes time to show results, but once it does – you’ll be more than happy with what you’ve achieved.

Five extra tips for achieving the best results

Here are a few tips to get the most effect out of your spaced repetition study sessions:

  • Practice at a level where there is a balance between your recalling success rates and error rates. If your error rate goes down significantly and you’re easily recalling all information then you’re no longer actively using your brain to retrieve information (and wasting valuable time).
  • Don’t give up and stick with your schedule even despite any rough patches of difficulty remembering things. These difficult moments are some of the most valuable as they will help strengthen your neural pathways over time.
  • Spaced repetition isn’t magic and it requires time and effort to see results. It’s simply an evidence-based memorization method with many benefits when used correctly and consistently.
  • Set up your study environment and make sure to have everything you need in one place. Having a well-organized, distraction-free, and comfortable study space is just as important as optimizing tiny features of your spaced repetition algorithm. Without a comfortable study space, your test results will suffer.
  • Try using spaced repetition with and without flashcards. While flashcard-based spaced repetition apps such as Anki are great for subjects such as language learning, they may not be as well-suited for complex subjects that require a more in-depth understanding of the material.

Frequently asked questions

How often should you use spaced repetition?

The optimal intervals with which you practice spaced repetition depend on multiple factors, such as upcoming exam dates, the difficulty levels of the information, and more. However, one of the most common algorithms involves repeating the information on the first, seventh, sixteenth, and thirty-fifth day after learning.

How do you practice spaced repetition?

Practicing spaced repetition involves these steps: Planning the spacing intervals of your study sessions, reviewing and studying the information for the first time, recalling the information at the first spacing interval, and continuing to recall the information at chosen intervals.

Why is spaced repetition important?

Spaced repetition is important because it is an evidence-based technique that helps your brain retain information more effectively, increases your speed of recall, decreases the time spent on study sessions, and improves test results drastically.