How Many New Japanese Words Should You Learn a Day? Spaced Repetition Explained

How many new Japanese words a day: 5 to 20

Most beginners should learn about 10 new Japanese words a day, and anywhere from 5 to 20 works. The right number is set by how much time you have for reviews, because every new word comes back for review for months.

So pick a number you could keep up every day for three months, and start at the low end. Kanji count the same way: each new kanji is one more item.

The next two sections say what to do and why reviews grow. After that comes the background: the forgetting curve, spaced repetition, and the two main ways apps schedule reviews, SM-2 and FSRS.

How many new words, and how many kanji, a day?

Some practical guidance, from the review arithmetic in the next section rather than from a study:

• Set the number by your review time. If your reviews regularly take longer than the time you have, add fewer new items for a week or two. The review count will fall on its own.
• Keep it steady. Ten new words every day gives a smooth review load. Seventy on Sunday and none the rest of the week gives spikes.
• Expect to miss about one in ten if your target retention is 90% (explained below). Missing many more than that usually means the new items are coming too fast, or an item needs a better example.
• Take a day off from new items, not from reviews. If you're busy, do only your reviews. Skipping reviews is what lets them pile up.

How many kanji a day?

Count each kanji as an item and stay inside the same 5 to 20 total. So 10 new words and 5 new kanji is 15 items, not 10.

Learn each kanji through a word or two you'll actually use (if kanji are new to you, start with what kanji are). Many kanji have more than one reading, and the word tells you which one to use. 日 is read differently in each of these three N5 words:

Some words go further. 今日 (きょう, today) is read as a whole: neither kanji has its own reading in it, so you learn it word by word.

In the kanji stages of our N5 path, that's about 10 kanji a stage, next to word stages of about 25 words.

Still learning hiragana and katakana?

The same rule works for kana: a few new characters a day, with reviews every day. Our guide to how long hiragana and katakana take gives a daily plan.

Why reviews grow with every new word

Here's the part that surprises people: the number of new words you add decides how many reviews you'll do later. A word isn't reviewed once. It comes back several times over the following months.

Under SM-2, the first interval is 1 day, the second 6 days, and each one after that is the previous interval × 2.5, rounded up to a whole day. For a word learned on day 0, the reviews fall on:

Now add the same number of new words every day. After about two months, each day you're reviewing the words you learned 1, 7, 22 and 60 days ago: four batches.

That's four reviews a day for every new word a day, even when you never miss. In practice it's more. The Anki manual puts it this way: "If you are consistently learning 20 new cards a day, you can expect your daily reviews to be roughly about 200 cards/day." The manual doesn't say how it got that figure. But real reviews include misses and extra steps, so it is far above the ideal case. The lesson is the same: reviews scale with new items, and they arrive weeks after you added them.

This is why the daily number of new items is the setting that matters. It's easy to add 50 words on a motivated Sunday. The cost arrives over the following weeks.

What 10 words a day adds up to

Small numbers add up fast. Here is the plain multiplication:

These are words you've met, not words you'll keep: you'll forget some along the way and relearn them. Compare them with how many words JLPT N5 needs, and with how long to study for JLPT N5.

"Knowing" a word also means more than one thing:

• Recognising it: you see 毎日 and know it means "every day".
• Recalling it: you want to say "every day" and まいにち comes to mind.
• Hearing it: you catch it when someone says it.

Recognising comes first and is the easiest. Recalling and hearing take more practice, and each one brings its own reviews. For where vocabulary fits in a full study plan, see how to learn Japanese step by step.

The forgetting curve

In experiments completed in 1880 and published in 1885, the German psychologist Hermann Ebbinghaus learned lists of nonsense syllables and measured how much he had forgotten after different delays. The result was the forgetting curve: memory drops quickly at first, then more and more slowly. In 2015, Jaap Murre and Joeri Dros repeated the experiment (one person, 70 hours of learning, relearning after delays from 20 minutes to 31 days) and concluded that the curve "has indeed been replicated".

Two things follow for learning Japanese:

• A word you learned today is at its most fragile in the next day or two. If you don't meet it again, most of it will go.
• Each successful recall makes the memory last longer. After a review, the curve starts again, but it falls more slowly than before.

That second point is the whole idea behind spaced repetition.

Spaced repetition: review just before you forget

Spaced repetition means reviewing each item at growing intervals: soon after you learn it, then a few days later, then a couple of weeks, then months. Each review is timed for when you're starting to forget. The idea is that a recall that takes a little effort does more for memory than one that's effortless.

The FSRS project, which makes one of these schedulers, describes the memory of each item with three numbers:

• Retrievability: "the probability that the person can successfully recall a particular piece of information at a given moment". It starts high and falls over time.
• Stability: "the time, in days, required for R to decrease from 100% to 90%". A new word has a stability of days; a word you know well, months or more.
• Difficulty: how hard the item is for you, which controls how quickly its stability grows after each review.

The scheduler's job is to bring an item back when its retrievability has fallen to a target you choose, the desired retention. With a target of 90%, it shows you each item when it predicts you have about a 90% chance of remembering it. That means getting about one review in ten wrong is expected, not a sign you're failing.

The target is a trade-off. The Anki manual explains that "at lower desired retention you will have to do significantly fewer reviews per day, but you will also forget more cards", and that as it "approaches 100%, the workload increases drastically".

FSRS vs SM-2, at a high level

SM-2 was created by Piotr Woźniak for SuperMemo, used in it from 1987 to 1989, and described in his 1990 master's thesis. It was the basis of the original scheduler in the flashcard app Anki, which now calls it its "legacy" algorithm. (Anki is one of the tools in our guide to the best websites to learn Japanese.) SM-2 is a fixed formula: intervals of 1 day, then 6 days, then each interval multiplied by the item's ease factor. The ease factor starts at 2.5, never goes below 1.3, and moves up or down with how well you answered. Miss an item and its repetitions start again.

FSRS (Free Spaced Repetition Scheduler) is a newer, open-source algorithm developed by Jarrett Ye and the Open Spaced Repetition community. Instead of a fixed formula, it models each item's difficulty, stability and retrievability, and its starting settings come from large collections of real reviews. The research it grew out of was published at ACM KDD 2022 and in IEEE Transactions on Knowledge and Data Engineering in 2023.

The practical differences:

Anki now offers FSRS as "an alternative to Anki's legacy SuperMemo 2 (SM-2) algorithm", and says that "by more accurately determining how much information you are likely to forget, it can help you remember more material in the same amount of time". The FSRS project says users need 20 to 30% fewer reviews than with SM-2 for the same retention. Those are the project's own figures. The project also publishes an open benchmark of scheduling algorithms, run on about 727 million reviews from 10,000 Anki users, linked in the sources.

For choosing how many new words to add, the algorithm matters less than the arithmetic above. A better scheduler reduces the reviews per word. It doesn't make them disappear.

How KanaMastery's Smart Review applies it

Smart Review (/review) is where everything you learn on KanaMastery comes back. It's built on the ideas on this page:

• FSRS schedules every answer, using the open-source ts-fsrs library with its default settings and a target retention of 90%. Intervals are counted in whole days.
• Each skill has its own schedule. Smart Review tracks recognising, recalling and hearing each item separately. So a word you practise in all three ways brings reviews for each of them, more than the per-word arithmetic above shows.
• The most at-risk items come first. When more is due than you'll do in a day, Smart Review picks the items you're most likely to have forgotten.
• Daily reviews are capped: 20 a day for free accounts and up to 100 for KanaMembers, and you can set a lower cap (as low as 5). A day's review never goes over the cap, however much is due: anything beyond it waits for another day, with the items you're most likely to forget at the front.
• Holiday mode pauses it. Going away for a week? Turn it on and you get no reviews until you turn it off. When you come back, the items you're most likely to have forgotten come first.
• New items come in stages. The learning paths pace what's new: N5 word stages have about 25 words, kanji stages about 10, and each stage opens when you've learned 80% of the one before.

Match your pace to your cap. At the free cap of 20 reviews a day, about 5 new items a day is the pace that keeps up, so a word stage over about five days. With a higher cap, a stage over two or three days lands you in the 10-a-day range. If more is waiting each day than you clear, slow down new stages or raise your cap.

Questions about how many words to learn a day

How many new Japanese words should I learn a day?

About 10 a day suits most beginners, and 5 to 20 all work. Choose by your review time: fewer if reviews already fill your day, more if you finish them easily.

Can I learn 20 Japanese words a day?

Yes, if you have time for the reviews that follow. In the ideal SM-2 case, 20 new words a day means about 80 reviews a day after two months, and the Anki manual says to expect about 200.

Is 10 words a day enough?

Yes, for most beginners. Ten a day is 300 words a month and 3,650 in a year, if you keep up your reviews.

Can I learn 100 words a day?

Not to keep them. You can meet 100 words in a day, but the reviews that follow would soon reach hundreds a day, a pace almost no one can keep up.

How many kanji should I learn a day?

Count each kanji as one item inside the same 5 to 20 total. Learn each one through a word that uses it.

How many words do I need for JLPT N5?

See our page on how many kanji and words JLPT N5 needs. It explains why there is no official list and what the unofficial ones contain.

How long do reviews take?

It depends on you and on the item, and no source we read gives a fixed time per review. Time yourself for a week: count your reviews and the minutes they take, then set your new words from that.

What if I miss a day of reviews?

Do the reviews the next day before adding anything new. The missed items will be a bit harder, and a few may be wrong, which is normal. If they've piled up, add no new items until the pile is gone.

Sources

• Murre, J. M. J. and Dros, J. (2015). Replication and Analysis of Ebbinghaus' Forgetting Curve. PLOS ONE 10(7): e0120644.
• Woźniak, P. (1990). Application of a computer to improve the results obtained in working with the SuperMemo method (the SM-2 algorithm, its rounding rule, and its use in SuperMemo from 1987 to 1989; adapted from his 1990 master's thesis).
• Open Spaced Repetition: the project on GitHub, ABC of FSRS (definitions, desired retention range, the comparison with SM-2, delayed reviews), SRS benchmark and ts-fsrs.
• Ye, J., Su, J. and Cao, Y. (2022). A Stochastic Shortest Path Algorithm for Optimizing Spaced Repetition Scheduling. Proceedings of KDD '22.
• Su, J., Ye, J., Nie, L., Cao, Y. and Chen, Y. (2023). Optimizing Spaced Repetition Schedule by Capturing the Dynamics of Memory. IEEE Transactions on Knowledge and Data Engineering 35(10).
• The Anki Manual, deck options: FSRS, desired retention and new cards/day.
• Richards, O. How Many Words Can You Learn Per Day? The Truth. StoryLearning (12 new words a day as "a sensible maximum").
• Smart Review and the learning paths: KanaMastery's own settings, as of the date above.
• Word readings: JMdict, © Electronic Dictionary Research and Development Group, CC BY-SA 4.0 (see our attributions page).
• Reviewed by two independent reviews; the kanji reading examples and the advice on learning kanji through words are waiting for a native speaker's check.