What is FSRS? How it differs from regular spaced repetition and Anki scheduling
A clear explanation of FSRS, how it relates to spaced repetition and the forgetting curve, and how Anki FSRS settings compare with Tomaru automatic FSRS vocabulary review.
What is FSRS? How it differs from regular spaced repetition and Anki scheduling
FSRS, short for Free Spaced Repetition Scheduler, is a scheduling algorithm that decides when a card should appear again. It is not a new vocabulary learning trick. It is the calculation layer behind spaced repetition. Compared with traditional spaced repetition scheduling, FSRS uses your actual memory performance on each card to estimate memory state and forgetting risk, then schedules a better review time. In simple terms: traditional methods schedule by rules; FSRS schedules by your memory performance.
What is FSRS?
FSRS stands for Free Spaced Repetition Scheduler. It is an open-source spaced repetition scheduling algorithm developed by researcher Jarrett Ye. Its core job is simple: based on your recall result each time you review a card, it estimates how strong that memory currently is and predicts when it may drop close to forgetting. It then schedules the next review near that point.
For a learner, FSRS feels like this: you review a vocabulary card, mark whether you remembered it or forgot it, and the system decides when that card should return. If you remembered it, the interval gets longer. If you forgot it, the interval gets shorter. But FSRS does not do this with only fixed rules. It uses a model that estimates memory decay, so each card's schedule can better match your actual forgetting rhythm.
How is FSRS related to spaced repetition?
This is the easiest point to confuse.
Spaced repetition is a learning method. Its core idea is to avoid studying everything at once or rereading the same list every day. Instead, reviews are spread over time and happen before you forget. The method uses the forgetting curve so each review happens when it is most useful for strengthening memory.
FSRS is a scheduling tool. It answers the question: “On which day should this card return?” Spaced repetition tells you to review across different time points. FSRS calculates whether this specific card should return tomorrow, next week, or three weeks later.
The relationship is: spaced repetition is the direction, FSRS is the navigation system. You can use spaced repetition with many scheduling systems. FSRS is one of them, and it is one of the more modern options for scheduling accuracy.
Why does vocabulary learning need scheduling?
Vocabulary learning has a practical problem: there are many words, and every word has a different familiarity level.
If you are learning 300 words, some are remembered after one encounter, some are still difficult after ten reviews, and some felt familiar yesterday but uncertain today. Manually deciding which words to review each day is almost impossible to do efficiently without missing important items.
A scheduling system solves this. It tracks the state of each card and automatically decides when it should appear again. Difficult words return sooner; familiar words get longer intervals. You only need to complete the reviews assigned for the day instead of deciding the entire schedule yourself.
Without scheduling, vocabulary learning becomes like reading a 300-word list from top to bottom every day, without knowing which words are stable and which need urgent reinforcement.
Traditional spaced repetition vs FSRS
| Criteria | Traditional spaced repetition | FSRS |
|---|---|---|
| Core logic | Uses fixed rules or multipliers to change intervals | Dynamically adjusts review timing based on estimated memory state |
| Review interval | Correct answers lengthen intervals; wrong answers shorten them to a fixed value | Calculates intervals for each card based on estimated memory decay |
| Response to personal performance | Relatively coarse, mostly based on right or wrong | More detailed, considers recall difficulty and review history |
| Hard vs familiar cards | Both follow the same rule system | Different cards can have different decay estimates |
| Beginner experience | Easier rules to understand | More accurate, but settings can feel more complex |
| Best use case | General card review and beginner use | Long-term tracking for many cards |
In short, traditional spaced repetition works like “correct means longer, wrong means shorter” with relatively fixed rules. FSRS works more like “estimate this card's current memory strength from its history and predict when it will be close to forgotten.” It is closer to your actual forgetting rhythm, but the calculation behind it is more complex.
For most users, the practical difference is that FSRS scheduling is less likely to bring back cards too early when they are already easy, or too late when they have already been forgotten.
How is FSRS related to the forgetting curve?
The forgetting curve describes a simple phenomenon: after learning something, memory does not stay at the same level. It naturally declines over time. Without review, much of it may disappear within days.
Spaced repetition uses this pattern by scheduling reviews before memory drops too far. Each review raises memory strength again and slows the next decline. In theory, if reviews happen at the right moments, fewer review sessions can maintain memory for longer periods.
FSRS tries to make the “right moment” more precise. Instead of applying the same rule to all cards, it estimates memory decay for each card independently. This helps reviews land closer to the point before forgetting, rather than too early or too late.
The forgetting curve is the phenomenon. Spaced repetition is the strategy. FSRS is a calculation tool that makes the strategy more precise.
What is FSRS in Anki?
Anki began integrating FSRS support in 2022, allowing users to switch review scheduling from the older algorithm to FSRS. For advanced users, this is valuable: they can set desired retention based on their learning goals, and the system can calculate appropriate workload and intervals.
But Anki's FSRS integration also adds learning cost. To use it well, users often need to understand desired retention, what FSRS parameters mean, how workload may change after enabling it, and whether different decks need different settings. This is not a problem for experienced Anki users, but for beginners it adds another layer of settings on top of an already flexible tool.
This is not a flaw in Anki. It is Anki's design direction: give users control over details. For some learners, that control is exactly what they need. For others, it is more than they want to manage.
Is FSRS good for vocabulary learning?
Yes. FSRS is a strong fit for vocabulary learning because vocabulary has several traits that need good scheduling.
First, vocabulary volume is usually large. Common words in a language can number in the thousands, and exam vocabulary lists often range from hundreds to thousands of words. Manual scheduling does not scale.
Second, familiarity differs by word. Some words stick after one encounter. Some remain difficult after many reviews. FSRS tracks memory state at the card level, so difficult words can appear more often while familiar words get longer intervals.
Third, vocabulary memory needs long-term maintenance. Remembering a word today does not mean you will remember it three months later. FSRS can bring long-term vocabulary back at appropriate times to prevent total forgetting.
The conclusion is direct: if you need to remember many words over time, spaced review with FSRS scheduling is one of the more efficient approaches.
How does Tomaru use FSRS?
Tomaru integrates FSRS spaced repetition into the vocabulary learning flow, so users do not need to configure or enable anything manually.
Tomaru's official free vocabulary decks cover exam preparation, daily situations, and common vocabulary. Learners can start directly without first organizing decks or judging deck quality. During review, your recall result for each card is used by FSRS to estimate memory state, and the system automatically decides when that card should appear again.
The process is transparent to the user: you review words, mark whether you remembered or forgot them, and the system handles scheduling. You do not need to understand retention, tune parameters, or study Anki's settings first.
Tomaru is a free, ad-free vocabulary app, and official decks are free. Its AI card creation feature can turn articles, lyrics, conversations, or news into reviewable vocabulary cards, expanding your learning material.
FSRS is not magic
One point matters: FSRS solves review timing, not every language-learning problem.
Even with good scheduling, each review still needs real recall. You should try to remember the answer first, then check it, instead of immediately flipping the card. Active recall is what strengthens memory. FSRS only helps make that action happen at the right time.
Vocabulary learning is also only one part of language learning. Knowing a word's meaning does not mean you can use it in the right context. Example sentences help with context, grammar practice gives words structure, shadowing supports language feel, and bidirectional translation improves expression. Tomaru places these exercises after card review so learned words can be used, not just recognized.
FSRS helps you remember vocabulary more efficiently. But after remembering words, you still need to use them.
How should you choose?
Choose based on your goal.
Choose Anki if you:
- Want full control over FSRS parameters and retention settings
- Need custom card formats and deck structures
- Have your own material and want to turn it into decks
- Are willing to study tool settings for maximum flexibility
Choose Tomaru if you:
- Want to start vocabulary learning with FSRS without studying settings first
- Need free, ready-made official vocabulary decks
- Want scheduling to work automatically without manual tuning
- Want card review to connect with grammar practice, shadowing, and translation
- Want a free, ad-free vocabulary learning experience
FAQ
What is FSRS?
FSRS, or Free Spaced Repetition Scheduler, is a spaced repetition scheduling algorithm. It uses a learner's recall result for each card to estimate memory state and forgetting risk, then decides when that card should be reviewed again. Compared with fixed-interval scheduling, FSRS better reflects each person's actual memory performance on each card.
Is FSRS the same as spaced repetition?
No. FSRS is a scheduling tool for spaced repetition, but they are not the same thing. Spaced repetition is the learning method: review before forgetting so memory becomes more stable. FSRS is the algorithm that calculates when a specific card should appear again.
How is FSRS related to the forgetting curve?
The forgetting curve describes how memory naturally declines over time. Spaced repetition uses that pattern to schedule reviews before forgetting. FSRS goes further by estimating memory decay for each card, so review timing can land closer to the point before forgetting instead of following fixed rules.
Is FSRS better than regular spaced repetition?
FSRS can be more precise than fixed-rule spaced repetition because it adjusts based on your actual memory performance for each card. But “better” depends on context. For users who want to understand and tune scheduling, FSRS can provide more precise review timing. For users who just want to study, the key is whether review feels smooth and sustainable.
Does Anki have FSRS?
Yes. Anki began integrating FSRS support in 2022. Advanced users can enable FSRS and set desired retention and related parameters. This is valuable for people who want deeper control, but for beginners it requires learning more concepts.
Is FSRS suitable for vocabulary learning?
Yes. Vocabulary learning involves many words, different familiarity levels, and long-term memory maintenance. FSRS tracks memory state card by card, letting difficult words appear more often and familiar words get longer intervals. This is more efficient than manual scheduling or fixed-cycle review.
Is there a vocabulary app with FSRS that does not require setup?
Yes. Tomaru is a free, ad-free vocabulary app with built-in FSRS spaced repetition scheduling. Users do not need to enable FSRS or tune parameters manually. They can start with free official vocabulary decks, and the system automatically schedules the next review based on each recall result.
Does Tomaru use FSRS?
Yes. Tomaru uses FSRS to schedule vocabulary card reviews. Each time a learner reviews a card and marks memory state, FSRS updates that card's schedule. The process runs automatically, so users can focus on learning vocabulary instead of studying algorithm settings.