Flashcards & spaced repetition: the science

It is not that you have a bad memory. It is that your brain is doing exactly what it is supposed to do: forgetting what it does not reinforce.

You have spent three hours studying a topic. The next day you remember half. A week later, a third. A month on, almost nothing.

The good news is that this mechanism is predictable. And what is predictable can be hacked. Spaced repetition is the technique that leverages how your memory works so you retain information long-term with minimal effort. Combined with flashcards and active recall, it is probably the study method with the strongest scientific backing.

Ebbinghaus's forgetting curve

In 1885, German psychologist Hermann Ebbinghaus published the results of an experiment that would change our understanding of memory. He subjected himself to memorising lists of nonsense syllables and measured how much he retained over time.

The result is what we now know as the forgetting curve. The drop-off is dramatic:

After 20 minutes: roughly 58% is retained.
After 1 hour: 44% is retained.
After 1 day: 34% is retained.
After 1 week: 25% is retained.
After 1 month: 21% is retained.

These percentages vary depending on the type of material (meaningful material is retained better than nonsense syllables), but the pattern is consistent: most forgetting occurs in the first hours and days.

The revolutionary aspect of Ebbinghaus's work was not just documenting forgetting, but discovering that reviewing at strategic moments radically changes the curve. Each time you review something just before you would have forgotten it, the curve flattens. The information lasts longer in your memory and you need fewer reviews to maintain it.

What is spaced repetition

Spaced repetition is a review system where the intervals between reviews increase progressively. Instead of reviewing everything at the same frequency, you review each concept just before your brain would forget it.

The concept is simple:

You learn something new.
You review it the next day.
If you remember it, the next review is in 3 days.
If you still remember, the next one is in 7 days.
Then 14, 30, 60 days...

If you fail at any point, the interval resets to something shorter. The system adapts to your actual performance with each individual concept.

The key to spaced repetition is that you do not review everything at the same frequency. Concepts you have mastered appear less and less often. Those you struggle with appear more frequently.

This optimises your study time in a way that manual review could never achieve.

The scientific evidence

The effectiveness of spaced repetition is not an opinion or a trend. It is one of the study techniques with the strongest empirical backing:

Cepeda et al. (2006) conducted a meta-analysis of 254 studies comparing distributed (spaced) practice with massed (concentrated) practice. The conclusion was clear: spaced practice improves long-term retention in virtually all contexts.

Dunlosky et al. (2013) evaluated 10 popular study techniques and rated distributed practice (spaced repetition) as one of the two with the highest utility, alongside retrieval practice (active recall).

Karpicke and Roediger (2008) demonstrated that combining spaced repetition with active recall (actively retrieving information rather than re-reading it) produces results superior to either technique alone.

What is active recall and why it matters

Active recall, or retrieval practice, consists of trying to remember information without looking at the answer. It is the opposite of re-reading or reviewing notes: instead of exposing your brain to the information, you force it to search for it actively.

When you try to remember something, your brain strengthens the neural connections associated with that information. It is like a path in a forest: the more you walk it, the more worn it becomes. If you only look at the path on a map (re-reading), the undergrowth stays. If you walk it (active recall), it clears.

Roediger and Butler's (2011) research showed that students who practised active recall retained 50% more information a week later than those who simply re-read the material the same number of times.

Why re-reading does not work

Re-reading notes creates a dangerous sensation: the illusion of fluency. When you re-read something, it feels familiar. Your brain confuses familiarity with knowledge. You think you know it because it rings a bell, but when the exam arrives and you need to retrieve the information without the text in front of you, you discover that familiarity is not the same as recall.

Active recall breaks this illusion because it forces you to check whether you actually know something before it is too late.

Flashcards: the perfect vehicle for spaced repetition

Flashcards are the most natural format for implementing active recall with spaced repetition. One side presents the question or prompt. The other, the answer. Your job is to try to recall the answer before flipping the card.

Why flashcards work

They force active recall. Each card is a mini-test. You are not reading the answer -- you are trying to produce it.

They are granular. Each card contains a single unit of information. This allows the system to treat each concept independently: if you have mastered concept A but not concept B, the system adapts to each one separately.

They are fast. A 15-minute flashcard session can cover 50 or 60 cards. It is a high-density practice format.

They are portable. You can do a session on the train, in a queue or between classes. Small fragments of study that accumulate.

How to create good flashcards

Not all flashcards are equally effective. There are principles that make a difference:

One idea per card. If a card tries to cover three concepts, you will not know which of the three you are getting wrong. Break the information into atomic units.

Specific questions, not vague ones. "Explain the Krebs cycle" is too broad for a flashcard. "What is the end product of the Krebs cycle per acetyl-CoA?" is concrete and assessable.

Use your own words. Copying verbatim from the textbook produces rote memorisation. Rephrasing in your own words shows you have processed the information.

Include context when necessary. If a concept can mean different things in different contexts, include the context in the question.

Reverse the cards when it makes sense. If you have "ATP -> adenosine triphosphate", also create "adenosine triphosphate -> ATP". Retrieval works differently in each direction.

Passive study vs. active study: the comparison

To understand why spaced repetition with flashcards is so superior, it is worth comparing the two approaches:

Passive study (what most people do)

Re-read notes several times.
Highlight text (without a system).
Copy summaries from the book.
Listen to class recordings.

These activities expose your brain to the information but do not force it to work with it. It is like watching exercise videos on the sofa and expecting to build muscle.

Active study (what actually works)

Attempting to answer questions without looking (active recall).
Explaining concepts aloud without notes (the Feynman technique).
Taking practice exams on the material.
Reviewing with flashcards and spaced repetition.

These activities force your brain to process, organise and retrieve information. The cognitive effort is greater, but it is precisely that effort that produces learning.

According to Robert Bjork's theory of desirable difficulties, learning is more lasting when it requires effort. Things you learn easily are forgotten easily.

The ones that require work stick around.

How ExamFlow implements spaced repetition

ExamFlow integrates spaced repetition directly into its flashcard system, eliminating the complexity of setting it up manually.

Automatic flashcard generation

The first obstacle to using flashcards is creating them. With ExamFlow, flashcards are generated automatically from the material you upload. The system analyses your notes and extracts concept-definition pairs, key data, cause-effect relationships and elements you need to memorise.

You do not have to decide what to put on each card or draft the questions. The system does it for you, and you can edit, delete or add cards as you see fit.

Adaptive repetition algorithm

Each time you answer a flashcard, the system records whether you got it right and your perceived difficulty level. With this information, it calculates the optimal time to show you that card again.

Cards you get right easily are spaced further and further apart. Cards you get wrong reappear soon. Cards you get right with difficulty are kept at an intermediate interval. The result is that your review time is automatically concentrated where you need it most.

Connection with exams

Flashcards and exams in ExamFlow share data. If you fail a multiple-choice question in an exam, that concept is reinforced in your flashcards. If you master a flashcard, that concept is less likely to appear in the next exam. It is an integrated system where each tool feeds the others.

If you want to learn more about how exam generation works, we have a detailed article on how ExamFlow turns notes into exams.

Practical plan: how to incorporate flashcards into your routine

The theory is clear, but what matters is putting it into practice. Here is a concrete plan for incorporating flashcards with spaced repetition into your study routine.

Short daily sessions

You do not need long sessions. Between 15 and 20 minutes a day is enough to keep the system running. The key is consistency, not duration. Fifteen minutes every day is better than two hours on a Sunday.

Time of day matters

According to studies on memory consolidation, reviewing flashcards at night before bed can be especially effective because sleep plays a fundamental role in consolidating memories. If evening is not possible, first thing in the morning is the next best option.

Combine with other techniques

Flashcards do not replace deep understanding. You first need to understand the material (by reading, making outlines, looking at examples) and then flashcards consolidate what you already understand. ExamFlow's intelligent viewer is perfect for that first phase. You can read more about how to use it in our article on the document viewer.

Recommended progression

Weeks 1-2: Start with the topics you have gone the longest without reviewing. The system will generate the flashcards and schedule them automatically.

Weeks 3-4: Add new material while maintaining the review of previous content. The daily load will stabilise because concepts you already master will appear less and less.

Month 2 onwards: The system will be in cruise mode. Most of your flashcard time will be spent on new material or concepts you find difficult, while what you already know only appears occasionally to keep it fresh.

Common mistakes when using flashcards

Creating too many cards at once. If you upload an entire syllabus and generate all the flashcards in one go, the review load for the first few days will be overwhelming. Better to go topic by topic.

Not reviewing on days you do not feel like it. Spaced repetition works because the intervals are precise. If you skip a day, the intervals get out of sync. Five minutes is better than nothing.

Memorising without understanding. Flashcards are for consolidating, not for learning from scratch. If you do not understand a concept, study it first and then memorise it.

Not editing the cards. Automatically generated flashcards are a starting point. If a question is confusing or an answer incomplete, edit it. Personalising the cards improves retention.

Conclusion

Spaced repetition is not a new or experimental technique. It is one of the most robust findings in cognitive psychology, backed by over a century of research. Combined with active recall through flashcards, it is the most efficient way to transfer information from short-term to long-term memory.

The traditional barrier to using it was logistics: creating the cards, calculating the intervals, keeping track. ExamFlow removes that barrier by generating flashcards from your material and managing the intervals automatically. Your only job is to review for 15 minutes a day.

If you want to see for yourself, create your ExamFlow account and generate your first flashcards. Your future self -- the one who does not go blank in the exam -- will thank you.