Putting in the hours to learn something is grueling enough, but forgetting what you learned and having to repeat the process is even worse. Sadly, the reality is that we forget most of what we learn in just a short period of time.
Consuming information is useless if you are unable to recall it. In The Owner’s Manual for the Brain, the book states that “learning entails two processes: acquiring and retaining.”
Acquiring is easy. Retaining is what’s difficult. While it’s unlikely to retain 100% of everything we learn, we can use an effective method to forget less and forget slower. That method is referred to as spaced repetition.
What is Spaced Repetition?
Spaced repetition is a studying technique that involves repeatedly reviewing information that you want to memorize at gradually increasing time intervals.
The objective is to review material just as you start forgetting it. You practice spaced repetition by studying the same material multiple times, while progressively increasing the time between each session.
If you have 15 financial formulas to memorize for a final exam, you would learn all 15 formulas for the first time several weeks before the test.
After the first time you learned the material, study again the next day. Then study the formulas 4 days later. Then again 7 days later. And so forth until the information is permanently stored in your long-term memory.
Now you can see why the method is called spaced repetition. You repeat the same study session over several intervals.
Why Spaced Repetition Works
Spaced repetition works by helping you flatten the forgetting curve and crystallize the material in your memory through repetition of effortful retrieval.
The Forgetting Curve
The forgetting curve is a chart that represents the decline in retention of material over time.
It’s easy to recall information when you have recently studied. As time passes, you quickly forget a large majority of the material. This study method tries to time that out so you end up studying again as forgetting begins to happen.
The forgetting curve was discovered in the late 19th century by Hermann Ebbinghaus, a German psychologist. Ebbinghaus conducted an experiment to test his memory.
He tasked himself with memorizing a list of random nonsensical syllables. Hermann would test himself to see how many syllables he could remember at various points in time after initially learning them. He recorded the results and the pattern resembled the line below.
As you can see, the slope of the curve is steepest at the beginning of the time axis. This represents how one forgets a majority of what they learn in the first few days. In fact, we forget around 80% of what we learn after the first day and around 90% within the first month.
That can be disheartening if you are trying to learn something new. Thankfully, it was also discovered that you can decrease the rate of decline by reinforcing the memory through repetition.
As you repeat the same study session (signified by each dot on the chart below), the memory crystallizes and the forgetting curve flattens out, meaning the rate of decline decreases. As the rate of decline decreases, more time will need to pass before you begin significantly forgetting.
For example, if you study something once, you’ll likely forget 80% of the material within a day. However, if you study multiple times through spaced repetition you may only forget 20% of the information within a day of the latest session.
This is the reason for the gradually increasing intervals. Since forgetting starts later as the memory becomes stronger, the intervals are spaced accordingly.
Spaced repetition also works well because of effortful retrieval.
In Make It Stick, an excellent book on learning and memory, the author frequently states that when retrieving or recalling information is more effortful, it results in greater retention.
If your intervals are appropriately spaced out, you will study material again just as forgetting begins to set in. When you practice as you are on the cusp of forgetting, it requires effort and brainpower to recall the information.
This effort will result in deeper and more durable learning.
The 2 Components of Successful Spaced Repetition
Spaced repetition is frequently used by med school students and those learning new languages. However, you can use spaced repetition to remember anything you want: formulas for an exam, historical events, responses to interview questions, musical notes, your relatives’ phone numbers.
To show you how to use spaced repetition, I’ll first break down the components of spaced repetition. Then, I’ll share two ways you can practice spaced repetition.
Let’s break down spaced repetition into its fundamental components. The idea is simple: study the same material for multiple sessions with each session gradually spaced father apart in time.
Effectiveness of the method is based on two components:
- How you are studying
- How your study sessions are scheduled
If either of the two are off, spaced repetition won’t benefit you to its full potential.
1. How you are studying
First, you want to make sure you are studying effectively. Let’s go back to our example of memorizing 15 formulas for an exam.
It’s common for college students to “study” by rereading their notes over and over. They repeatedly read the formula list hoping they will remember the material. This is called rote memorization, and it’s a form of passive learning that has been proven to be one of the most inefficient ways to learn.
A better option is to test yourself on the 15 formulas through effortful retrieval, which we mentioned earlier. Effortful retrieval is a form of active learning that involves recalling facts from memory.
Rather than reading the formula for free cash flow, ask yourself:
“What is the formula for free cash flow?”
Then try to recite or write down the formula before checking the answer. This method is far superior for retention than rereading.
With that said, I would recommend that your study sessions for spaced repetition involve recall.
One of the best ways to practice recall is through flashcards. In our example, if you wanted to memorize 15 formulas, you would create 15 flashcards. On one side would be a question asking for the formula and on the other side would be the answer.
2. How your study sessions are scheduled
Now that you are studying effectively, the next part to focus on is the schedule. We know that we are supposed to progressively increase the time between each study session, but how much time is optimal?
There are common schedules that are recommended, but no one size fits all schedule to follow. Note that the goal is to study again just as you start forgetting the information from the previous study session.
The forgetting curve and schedule can differ depending on many factors. Examples include:
- The topic you are studying
- Your interest in that topic
- How effective your previous session was
- When you are trying to permanently learn the material by
If your test is in a month and you have to memorize formulas, you could stick to the schedule below with the following time between study sessions:
If you wanted to remember a song on the piano for the long-term, you could follow a more relaxed spaced schedule:
These two schedules greatly differ on the amount of time between each session. As I said, there is no one size fits all option. You would approach learning something for a test in a month differently than learning something to remember for life.
2 Ways to Practice Spaced Repetition
There are two great ways to use spaced repetition to remember more of what you are learning. They both involve flashcards. The first uses physical flashcards and the second uses digital flashcards via an app or software on your phone, tablet, or computer.
Use the Leitner box system
The Leitner box system was first proposed in the 1970s by Sebastian Leitner, a German science journalist.
The system uses flashcards and spaced repetition. It involves taking a deck of flashcards and creating several groups. These groups (boxes) are separated based on how well you know the information on each card.
If you have 5 boxes, each group would represent how familiar you are with the cards. Box 1 would hold the cards that are newest to you or cards you are having the most trouble with. Box 5 would hold the cards that you are most familiar with.
Each box would have a schedule for how often you study that group.
Box 1 is reviewed every day. Box 2 is reviewed every other day. And so forth until Box 5, which includes the “retired” cards. These are cards you review before the day of the exam because you feel like you have them completely memorized.
When you initially study your deck of flashcards, place each card in a box depending on how well you know the material. After each card has been placed in a box, follow the study schedule of each box.
With each session, move cards from one box to another based on your understanding. If you are struggling with a card, place it in a group that is studied more frequently. If you have mastered a card, move it to group 4 or 5 so it is studied less frequently.
Use an app
The Leitner box system is a great hands-on approach to study flashcards. An alternative is to use an app.
Many apps and software have been created for spaced repetition. They allow you create countless cards that you can access on your phone, tablet, and computer. Depending on what you are learning, you could find yourself creating 1,000+ cards. Now you can access your cards without having to carry them.
The real value comes from the algorithm. These apps have an algorithm that schedule how often you’ll see a card. This takes the scheduling hassle off your hands.
The app that is widely used (myself included) is Anki. With Anki, you can create your own flashcard decks and view the decks created by others. Friends in your classes can share decks with you and you can share your decks with them. I personally create my own decks because the act of creating the cards helps me learn.
Anki has a free application that can run on your computer. There is also a mobile app you can use, though it does cost $24.99. I use the mobile app on my iPad because of the additional tools and convenience it offers.
With Anki, you can add a variety of content and customization to your flashcards. A few examples include:
- Text (with formatting features)
- Annotation (Anki has Apple Pencil capability)
- Photos from your camera or photo album
When you study cards, the app will ask you how well you knew the information. If you knew the information, it will show you the card less frequently. If you struggled with the card, the app will show you the card more often.
Between the Leitner box system and the Anki app, I prefer to use the Anki app.
Usually, physical flashcards are superior to digital flashcards because you have to write and create them yourself. This helps with retention.
Since the Anki app is compatible with the Apple Pencil, I can still get the benefit of creating the cards from scratch. The additional tools and features are a bonus.
Try them both out and see which you like better!
Things to Remember When You Practice Spaced Repetition
Remember the three things below when you practice spaced repetition. The method is very simple, but very effective.
1. Try to space out your study intervals so the next study session takes place just as you begin to forget the material.
2. When you practice spaced repetition, your method of studying should involve retrieval. Test yourself and recall the information before reviewing the answers. Don’t study by rereading material.
3. Your learning will be deeper and more durable if it’s effortful.
Other Learning Resources
When it comes to remembering what you have learned, spaced repetition is the way to go.
Retention of material you learn quickly fades within hours, with 80% of the material forgotten in a day. Don’t waste any more of your time having to relearn. Implement spaced repetition and your memory will become stronger.