How Spaced Repetition (SRS) Can Help You Learn a New Language
Last updated: January 6, 2025
The decision to learn a language near immediately confronts learners with a conundrum:
- Their memory isn't that good (they think)
- They need to learn thousands of vocabulary words (at least)
Dire situation indeed!
And I'm now going to make a bold claim:
Chances are, you don't have a bad memory. You just aren't using it right.
Enter spaced repetition, an evidence-based strategy to efficiently commit information into your long-term memory—commonly used for vocabulary retention in language learning, but also applicable to basically everything that involves remembering anything.
- What is spaced repetition?
- The (awesome) science behind spaced repetition systems
- Spaced repetition for beginner, intermediate, and advanced language learners
- Are there any limitations to spaced repetition?
- Spaced repetition apps for learning a language
- How to get started with your spaced repetition system
What is spaced repetition?
Spaced repetition is an evidence-based approach to transferring information from short-term memory into long-term memory—i.e., remembering stuff. It consists of just two steps:
- Repetition, or reviewing the thing(s) you hope to remember
- Spacing, or doing this review at gradually increasingly intervals of time
Here's a visualization of a simple and manual approach to spaced repetition, called a Leitner system:
What you're seeing is:
- Everything you wish to remember goes into box #1 in the form of flashcards
- After reviewing the contents of box #1:
- Everything you get correct goes to box #2
- Anything you get wrong remains in box #1
- Review schedule:
- Box #1 is reviewed daily
- Box #2 every 3 days
- Box #3 every 7 days
- Box #4 every 2 weeks
- Box #5 once per month
- If you get an item wrong at any point, it goes back to box #1
And below you can see a demonstration of a (slightly different) Leitner system in action:
This does awesome things for your memory—we'll get into all that juicy stuff in the next section—but, as you can probably imagine just by looking at this GIF, it's kind of unwieldy to manage manually. Your desk can only fit so many shoe boxes, and if you keep this up for more than a month or so, you'll need an advanced degree in mathematics to manage your study calendar. (Trust me on this one.)
For these reasons, the job of scheduling flashcards for review is normally delegated to an algorithm—a computer program that automates the process of figuring out what you should review and when. Such programs are called spaced-repetition systems, or SRS for short.
The (awesome) science behind spaced repetition systems
About a hundred and fifty years ago, a German psychologist named Hermann Ebbinghaus posed a very practical question about memory:
If you learn a random tidbit of information today, and then never review it, how long will you remember it?
The results were, frankly—well, just look for yourself (Stahl, 2013):
Yeah. That's pretty bad.
It actually gets worse: only 2.4% of people who get certified in CPR today will remember how to do it in 3 years. This phenomenon has been dubbed the "forgetting curve"—but, let's be real, it's more like a "forgetting cliff"—and has been replicated by dozens of academic experiments.
TL;DR — Not reviewing information is, essentially, choosing to forget it.
But enough of that. I said that the science is awesome, not demoralizing.
Take a look at this next chart for me:
Much more palatable, isn't it?
Here's another glowing recommendation of spaced repetition from some really smart people:
...The spacing effect refers to the finding that long-term memory is enhanced when learning events are spaced apart in time, rather than massed in immediate succession (see Ebbinghaus, 1885/1964, for the first study on the spacing effect). The spacing effect is arguably the most replicable and robust finding from experimental psychology. Hundreds of articles, including a number of reviews (e.g., Dempster, 1988) and meta-analyses (e.g., Cepeda, Pashler, Vul, Wixted, & Rohrer, 2006), have found a spacing effect in a wide variety of memory tasks.
Just take a glance at this graph from the study:
What this chart is showing:
- Massed learning (doing 4 hours of study in one day, also known as cramming) generated very poor results
- Clumping study sessions (2 hours over 2 days) provided much better results
- Spacing lessons out (one hour daily over four days) provided significantly better results with complex tasks (tasks that involve processing information and extrapolating a solution)
So, the science is clear! You can get significantly better results by simply spacing your learning out, even if you're otherwise covering the same content in the same way and not trying any harder. It's free value for no additional effort. Where else in life do you get that?
Anyway, back to the article:
You see, the only thing you need to do to stop things from falling off the forgetting cliff is to review them once in awhile. And this is what makes spaced-repetition systems so cool. They do complex math stuff behind the scenes to answer three important questions for you:
- What should you learn next?
- What will you probably forget if you don't review it today?
- What do you still remember pretty well, so you don't need to review it right now?
What exactly your SRS does to answer those questions is beyond the scope of this blog post—read this one, if you dare—but the result is that, each day, your SRS will (a) give you a few new flashcards to learn and (b) suggest old flashcards that you should review.
What's more, these calculations become more accurate over time:
- Stuff that you consistently get right, you review less often
- Stuff that you consistently get wrong, you review more often
In other words:
Spaced-repetition systems guarantee that you spend more of your time practicing the things you need to practice and waste less of your time reviewing things you already know well.
Oh—and you end up spending a vastly smaller amount of time reviewing than you would by reviewing "normally", too! It's really just a wonderful thing all around.
Spaced repetition for beginner, intermediate, and advanced language learners
So, yeah—spaced repetition is grand. Glimmering. Smack dab glorious. Before we get into the most popular SRS apps and how to fit them into your schedule, though, you should know that the value you get out of them will depend in part on the level you're at with the language you're learning.
(If you want to explore this in a bit more detail, check out our deep dive into the five stages of language learning.)
If you're a beginner
Check out this blog post to see the math, but know that you'll need to learn about ~1,500 words before consuming content in the language you're learning starts feeling reliably doable. That's quite reasonable, when you consider that a college-educated native speaker knows around 30,000 words... but 1,500 vocabulary words is still a lot of stuff to memorize.
At the beginner level, a spaced-repetition system serves as something like bumpers in a bowling alley or training wheels on a bicycle. It lets you reduce the entire world of your target language down to a single sentence. While you may not be ready to read a book or listen to a podcast quite yet, you likely can work your way through one specific sentence, even if you've literally just began studying your target language earlier today and have to look up every single word.
As such, what SRS does is create an environment where you can interact with your target language in your target language, even as a beginner who still has a lot to learn.
This will be challenging, but the good news is that the harder you try to remember something, the more you build your memory. You're either remembering stuff or taking concrete steps toward remembering stuff. Glorious.
If you're at the intermediate level
Upon reaching the intermediate level, the bulk of your learning will come from consuming content in the language you're learning. Your flashcards now act as a force multiplier upon those gains.
Remember that first chart we looked at, showing how you'd basically forget everything you didn't review? That still applies here†.
When you interact with the language you're learning—whether you're reading a book, watching something on Netflix, listening to a podcast, or even having a conversation—you are, necessarily, encountering words, grammar points, and sentences in your target language. This is a natural form of review. It's also really effective.
In fact, because most words are used in a variety of ways and tend to appear next to certain words more often than other words, this "natural" review is of supreme importance. The context you get by seeing words used in a variety of natural formats is what will make your language feel, eventually, less foreign.
Importantly, though, words are not created equally.
Some words are much, much more common than others—especially in certain contexts.
What this means is that while interacting with your language is a great way to review and flesh out your understanding of old words, it isn't necessarily an efficient way to learn new words. These new words you're learning are relatively specific and sort of rare, and you likely just won't encounter most of them often enough to commit them to memory sheerly by consuming content.
Now, having said that:
Here, at the intermediate level, you're capable of deciding how you maneuver around this statistical reality.
If you're into math, you can get into the nitty gritty of it in this blog post. If not, there are two particular takeaways I want you to notice:
- Time spent on flashcards is linear—if you spend 10 minutes doing flashcards instead of 0 minutes, the only thing it costs you is 10 minutes
- Return on investment from flashcards is much more than linear—it enables you to regularly see words that you might otherwise see only once in several hours of interacting with your target language, meaning that SRS enables you to remember things that you might not remember without SRS
So your goal at the intermediate level is to strike a balance that feels optimal to you. While you want most of your time to be going toward things that involve you interacting with your target language, your SRS will enable you to more quickly remember the key words you need to understand the content you personally find interesting.
If you're at the advanced level
By this point, you probably know what you're doing! Or, at least, whatever you've been doing has apparently been working for you.
But if you're reading this blog post because you haven't used a spaced-repetition system so far and are wondering if it can help you, too, the answer is yes.
As you've likely noticed—the words you're learning now are pretty rare.
For you, an SRS is basically an insurance policy—anything that you make a flashcard out of will eventually make its way into your memory, too.
Are there any limitations to spaced repetition?
As incredible a tool as SRS is, it isn't all-powerful.
The nature of memory
To oversimplify a bit a lot, memory is a three-stage phenomenon:
- Encoding, in which information makes its imprint upon the synapses in your brain
- Consolidation, in which your brain strengthens and stabilizes those connections
- Recall, in which you access that information to make use of it
Spaced repetition is primarily for the last step in that process:
- Encountering words in the natural and vibrant world of native-language content provides more salient grounds for effective encoding to take place
- Consolidation happens primarily during sleep, during which time your brain fires the same signals it fired during the way when you were awake
Kicking off the process of any memory is a neuron that either does or doesn't fire, and you unfortunately can't force your brain to remember something nor choose what you remember. However, importantly, from that same study linked above:
"...Numerous studies now show that memory consolidation is facilitated by repeating the material over time but that all iterations are not created equal (7,15,21-26,35-37). As a general rule, memory improves as the spacing between presentations of repeated information is increased up to a point (21)."
Here's a really cool article about how memory works. It's eight pages long and taken from a magazine, so it's quite readable.
I'm not a scientist, so I'm not going to break it down, but I'll kind of thread the key points together for you:
"...Information destined for what is known as declarative memory—people, places, events—must pass through the hippocampus before being recorded in the cerebral cortex."
"...A neuron is like a microprocessor chip in that it receives thousands of signals through its dendrites and constantly integrates all the input it receives from these connections. But unlike a microprocessor that has many output wires, a neuron has only one, its axon. Thus, a neuron can respond to inputs in only one way: it can either decide to send a signal on to the next neuron in the circuit by firing an impulse through its axon, or not."
"...Both long- and short-term memories arise from the connections between neurons, at points of contact called synapses, where one neuron’s signal-emitting extension, called an axon, meets any of an adjacent neuron’s dozens of signal-receiving fingers, called dendrites. When a short-term memory is created, stimulation of the synapse is enough to temporarily “strengthen,” or sensitize, it to subsequent signals. For a long-term memory, the synapse strengthening becomes permanent.""
"...Although the process is poorly understood, investigators know that permanent strengthening to form long-term memories requires the postsynaptic cell to manufacture synapse-strengthening proteins (left).
"...How does a gene “know” when to strengthen a synapse permanently and when to let a fleeting moment fade unrecorded? And how do the proteins encoded by the gene “know” which of thousands of synapses to strengthen?
"...The same questions have implications for understanding fetal brain development, a time when the brain is deciding which synaptic connections to keep and which to discard. ...To strengthen the synapse permanently, a protein called CREB must be activated ...CREB, for instance, is activated by calcium-dependent enzymes that phosphorylate it and inactivated by enzymes that remove the phosphate tag. But there are hundreds of different transcription factors and protein kinases in a cell. ...What is the synapse-to-nucleus signaling molecule that determines when CREB should be activated and a memory preserved?""
Like many of life’s decisions, the neuron’s choice to cement a connection comes only after its importance has been demonstrated.
"...Like Leonard in Memento or any witness to a crime scene, one does not always know beforehand what events should be committed permanently to memory. The moment-to-moment memories necessary for operating in the present are handled well by transient adjustments in the strength of individual synapses.
But when an event is important enough or is repeated enough, synapses fire to make the neuron in turn fire neural impulses repeatedly and strongly, declaring “this is an event that should be recorded.”
The double-edged sword of context
Donald Hebb, one of the first to study memory from a neurological perspective, and whose work is still highly regarded, also came up with this mic drop of a quote:
Neurons that fire together, wire together.
What the quote means is essentially that we tend to associate things that happen simultaneously.
And, bad news for the flashcard learner, is that you will likely find that there are many words you know you know... but you can only remember when doing flashcards. To remember the word, you need the specific context provided by the sentence you learned the word in, by the voice of the person narrating it, and so forth.
Or, somewhat similarly:
Words don't exist in a vacuum
Perhaps the most important limitation of flashcards is that every single word exists within a complex web of meaning—you don't just know that pizza exists, you also know that it's something you eat, that it's delicious, that it's technically a pie, that it's supposedly from Italy, and all sort sof little things like that.
All that stuff is what makes pizza, well, pizza.
When you learn a word in a spaced repetition system, all you're really doing is learning that it exists—making a connection from a word in your native language to a string of sounds in the language you're learning. That's a very shallow connection—a pale imitation of the word as it is for native speakers.
With that in mind, here's a golden rule for you:
When you make a flashcard out of something, it's like you get a cup.
As you interact with your target language, you fill that cup with water.
Spaced repetition apps for learning a language
Way back up in that first section you saw how troublesome it was to manage a spaced repetition system by hand. Thankfully, enough people were annoyed by this problem that tons of solutions exist to it.
Pretty much every major language learning application will have you reviewing the things you learn according to a spaced repetition algorithm, and there are even several apps that are basically spaced-repetition enhanced flashcards on steroids.
Here's four different SRS apps and platforms that are worth looking into:
Quizlet, great for if you work with a tutor
I initially hesitated to add this one to this list because I've only actually used it once.
So, why am I recommending Quizlet if I didn't actually end up using it?
Three main reasons:
- It's incredibly easy to set up—like I'm not even going to give instructions; you'll figure it out without any trouble
- It's collaborative, so people can build decks of flashcards and share them in real time
- It's free, unless you're planning to teach a class with it or something like that
The one time I used Quizlet was after an italki lesson. I had a conversation with a Korean teacher, and at the end of the lesson he was like, "Hey, so here are a few words and sentences you messed up several times today. I made flashcards for them. You can review them for next week." And then he sent me a link and it had a pre-made deck of about 15 flashcards. And I was like, "Huh, that's actually really cool."
It was, actually, really cool.
I didn't use the flashcards nor did I continue to use Quizlet—if you're reading this, Hyunku, sorry—but I was impressed. I wish that my teachers in high school would have used Quizlet.
If you think SRS sounds interesting but you're hesitant to learn a bunch of new stuff—go ahead and give Quizlet a shot. You'll outgrow it quickly if you take this remotely seriously, but if you're just curious about the Good News, Quizlet is the easiest way to see what spaced repetition is all about.
Anki, an SRS app for power users and/or those who like to tinkerer
Ahh, Anki. The original open-source SRS flashcard tool that's free on desktop and Android but $24.99 on iOS. (🍎📱😭).
Anki's biggest strength is also its biggest weakness: it's nearly infinitely customizable. You can do incredible things with it, and people have made all kinds of decks of flashcards and shared them publicly. There is even a community of people making addons for it, but it has a learning curve.
Migaku actually used to be one of those Anki addons. Below is an example of an old Migaku flashcard type for Anki, used by one of our users who set a goal of learning 4,000 Spanish words in 4 months.
If you're good with computers and like tinkering with things to get them just right, you'll probably like Anki. If you think it might be for you, I recommend you to click through those links I shared up above and see if something catches your eye.
Memrise, if accessibility is more important to you than flexibility or efficiency
For a long time, in the world of spaced repetition online, there was Anki and there was Memrise.
Whereas Anki was—and I say this lovingly—an ugly piece of confusing software, Memrise was elegant and easy to use: you just logged in, and so long as you had the minimum knowledge necessary to navigate the internet, that was enough to learn from and create spaced-repetition enhanced courses. Yeah—not just decks, but courses. People went ham, taking entire textbooks and building chapter-by-chapter flashcard-based companion courses for them. It was one of the few times in internet history where a community of strangers came together and made something beautiful for no real benefit to themselves.
Memrise recently shelved all of those community courses in favor of a more corporate-feeling AI app. The new Memrise retains the pleasant UX and impressive accessibility, and they've also done an impressive job of taking something like YouTube Shorts or TikTok reels and combining them with flashcards. It's cool, sort of... but it's not the Memrise I knew and loved, and not something I recommend anymore.
Having said that, if design is super important to you, or you really like the idea of learning words and sentences by seeing native speakers say them, it's worth giving Memrise a shot.
Migaku
Migaku is the SRS flashcard app to rule them all.
(Full disclosure, if you haven't noticed: You're reading this on Migaku's blog, and I may or may not be slightly biased.)
I say that so confidently because we are a group of (ex) power Anki users who learned languages to a high level—I've personally passed the highest level proficiency test of Japanese and a similar test of Mandarin—and found ourselves in an awkward situation:
Anki was irreplaceable when it came to learning a language... but it wasn't designed for language learners.
That will be apparent to anybody who uses the app for more than a few hours. Anki is great... but it could be so much more.
And that's why we made Migaku.
It delivers the performance that power users demand, but it's also got the user-friendly UI that helps Memrise win users. It was also designed explicitly for language learners—not just to review flashcards, but to make them.
Like, check this out:
What you're seeing is somebody watching YouTube, finding a useful word, clicking one button, and then creating a high-quality flashcard directly from the video. On your phone.
You could do that with Anki, but not on your phone. You'd need to be on your computer and really have your process down. It'd take like seven minutes of manual work and the end result wouldn't look as nice. (Our flashcards look really nice.)
Migaku is just kind of this cool bit of technology that takes the best elements of several other spaced-repetition services and puts them into one convenient package for language learners. It's great—and you can try it totally free for ten days.
How to get started with your spaced repetition system
Alright! So now we're cooking. You understand how SRS can make your life better, you've picked an app that suits your style, and you're ready to memorize over nine thousand vocabulary words in like six days.
As you start working SRS into your routine, here's a few things to remember:
Trust me, start with like 3 new cards per day
Speaking on behalf of literally every single learner who has discovered spaced repetition before you, here's how your first day with an SRS tool is going to go:
- You get your SRS of choice set up
- You spend half an hour trying to find a good-looking deck
- You find one you love
- You're hyped
- You do your system-recommended 10 flashcards
- It takes like 3 minutes
- You're done
- ...You're done?
- ???
- But you just got started! You're not ready to be done yet.
- You roll up your sleeves and add like 40 more cards, because you're taking this seriously 💪
- You finish your 50 new words—man, this is what you've been missing!
- You close the app for the day, feeling like a superhero of productivity
Please—for the love of all things that are sacred, don't do that to yourself.
You see, the nature of any SRS is that they take a bit of time to really get up to speed.
What do I mean by that?
Well, remember how back up in section one, when we looked at the Leitner system, it had you reviewing flashcards on five different intervals—every day, every 3 days, every week, every other week, and every month? What this means is that while today you're just learning 10 cards... on day 30, you'll be learning 10 more cards, but also reviewing 5 days worth of cards, so you might actually be seeing sixty flashcards.
You can see where this is going.
If you've been going ham and doing like 30 new cards per day, you'll be reviewing like 200 cards per day within a few weeks. It will be a miserable nightmare, you'll hate your life, you'll burn out, and may quit learning your language altogether.
So do yourself a favor and don't do that.
Here's how to start a spaced repetition app:
- Initially, do just 3 new cards per day
- Keep this up for about two weeks—it'll feel really, really, really slow at first, but will pick up as you go
- If you finish all of your flashcards every day for two weeks straight, and you aren't feeling strained, add three more cards—start doing 6 new cards per day
- Repeat step 3 until you begin regularly (once per week) failing to complete all of your scheduled flashcards; this is your personal SRS limit for the amount of time you have available to give to your language
Take advantage of the serial-position effect
Hermann Ebbinghaus, the guy who who discovered the forgetting curve, which we discussed above, also made note of what he called the serial-position effect: we tend to remember the first and last things we study in a given session better than what came in the middle.
You may have heard the advice that several short study sessions beat one long one, and this is the reason for that:
- A single 2-hour study session gives you one start and end
- Ten 12-minute study sessions give you 10 starts and 10 ends
So, don't just sit down and knock out all of your spaced repetition "homework" in a single block of time:
- Do flashcards while going to the bathrooom
- Do flashcards while waiting on a meeting/class to start
- Do flashcards while walking
- Do flashcards during those little pockets of time when you'd otherwise pull up social media
Once you start looking, you'll be shocked to find that your day is full of little two and three minute blocks of time that are too small to really do anything... but are absolutely perfect for flashcards.
I personally do ~200 flashcard reviews per day, but I never actually intentionally sit down to do flashcards. They all get done gradually throughout the day, which leaves me a longer block of uninterrupted time in the evening to consume content in the language I'm learning.
Remember that flashcards and input† go hand in hand 💪
When you first start doing spaced repetition, it's going to feel like a superpower. Plus, it's fun watching the number go up. You're going to download some awesome deck (such as the Migaku Academy!) that has like 2,000 flashcards, and you're going to want to knock all of them out as soon as possible.
Don't do that.
Remember our golden rule from above:
When you make a flashcard out of something, it's like you get a cup.
As you interact with your target language, you fill that cup with water.
Flashcards are the perfect way to complement the input you're getting, but they should never replace your input. Remember: you're here because you want to do something awesome in the language you're learning, not because you want to memorize the dictionary and become a Scrabble champion.
(† Note: input refers to consuming content in your target language, such as reading a book or watching YouTube)
Make your own flashcards
There are a lot of shiny decks of flashcards out there on the internet that people have put a lot of time into building. It's commendable, and it's a beautiful thing that these people are willing to give their time to support the common good.
Beyond one single deck to learn the most common ~1,500 vocabulary words or so, though, you shouldn't be using these decks.
We talk about this more in our post on how to learn vocabulary, but words aren't made equally. Some words are used much more commonly than other words, and the words that are super important if you want to read (say) fantasy novels may be totally useless if you want to watch (say) Spanish YouTubers talking about soccer.
- With a premade deck of flashcards, you don't know where the vocabulary was sourced from, so you can't really know if the words will be useful to you
- With a deck you make yourself, though, you can be 100% confident that the cards you make yourself will be of use to you
Why?
Because you are consuming content you are interested in, and making flashcards out of the words you need to understand this content.
If you learn to make your own flashcards, you can effortlessly turn anything into a learning opportunity.
Pace yourself for a marathon
This is similar to the first point, in which I asked you to start with 3 flashcards per day. This point is so important that I'm going to come at it again from a different angle.
I first set out to learn Korean about five years ago. It would have been my fifth language, and since I already spoke Japanese and Mandarin quite well, it should have been super easy. (Morgan Freeman's voice: it wasn't.) I even wrote a lengthy plan detailing exactly how I was going to learn Korean, which you can skim here.
What you'll notice, if you creep my Reddit profile, is that I only made a single update in that 24-month plan. I got burned out and gave up within the course of about three weeks.
I recently got back into learning Korean a few months ago, and, to date, Migaku says I have learned about 750 words.
That's great... but it also means that, five years ago, if I would have committed to learning just one card a day, every day, I'd be nearly three times further along than I am right now.
As excited as you might be feeling right now—just know that you'll make much more significant progress if you approach learning in a sustainable way that you actually keep up.
You will optimize things as you go along, and as the language you're learning becomes a more important part of your life. Until then, remember that a mediocre workout done religiously will out-perform a perfect workout that you never do.
In other words
Yes, spaced repetition is great, and you should be using it. It won't learn a language for you, but it will enable you to effectively consolidate the things you learn so that you can make steady progress, and it will also prevent you from forgetting the things you learn.
Whichever SRS app you go with, just remember the golden rule:
Spaced repetition complements, but should not replace, input:
When you make a flashcard out of something, it's like you get a cup.
As you interact with your target language, you fill that cup with water.
With that said, get out of here and go do something awesome in the language you're learning 💪