What makes a good spaced repetition system? (WaniKani)

Wed, 15 Apr 2026 05:17:00 +0000

This is part 1 of a ~3 part post. This part explains how WaniKani works through my first experience and follies using a spaced repetition system.

Japanese is one of the world’s most difficult writing systems. Compared with English, Hiragana and Katagana are simple phonetic alphabets. Their pronunciation is always consistent, and across both alphabets there’s just ~92 distinct characters plus a handful of consistent diacritics and multi-character compounds. Much easier than English where “ghoti” could arguably be pronounced “fish”¹.

But to read Japanese, you also need to be able to interpret at least 2000 Kanji characters. Most Kanji characters can be pronounced at least two different ways depending on context: a native Japanese pronunciation (kun’yomi) in addition to the pronunciation derived from Chinese (on’yomi). For common characters there’s usually at least one or two more. In the worst cases, for example 生, an extremely common character that Japanese children learn in first grade, a single character can have as many as 6 different kun’yomi and 2 different on’yomi.

I knew all of this when I set out to learn the 2000 most common Kanji. I’d just returned from my first trip to Japan, and was more motivated to learn than ever.

WaniKani

WaniKani made getting started frictionless. Kanji can be broken down into radicals, bits of characters with a consistent meaning/shape. Each WaniKani level, starts off with lessons teaching you the names of the radicals. Each radical is taught with a mnemonic and often comes with a cute picture too:

Since there are no circles in Japanese characters, sometimes rectangles or squares have to make do. In this case, this big rectangle is the sun. The middle line is a cloud, moving across the sun. Picture it, but don’t actually look at the sun and burn your eyes!

After a couple hours, you prove that you remember the names of each of the radicals by typing them out, and then you’re done for a few hours. You review the radicals again, then again after a day, and finally if you’ve gotten the item right 4 times in a row, you’ve proven that you’ve committed the radical to your “medium-term” memory. The radical upgrades from the “Apprentice” to the “Guru” memory stage, unlocking Kanji that depend on that radical. For Kanji there’s two separate things you learn and are tested on: meaning and pronunciation. When a Kanji advances to “Guru” you unlock dependent vocabulary, again with separate meaning and pronunciation lessons. Once all but 3 Kanji in a level are “Guru”, you advance to the next level, unlocking the next set of radicals.

At first, it only took 5-10 minutes a day to do all of my reviews plus new lessons. I returned to WaniKani for my reviews after the exact review time intervals, to make sure that do my reviews as soon as possible. Because I was also maintaining a high accuracy, I was able to advance a level every ~8 days. Projecting forward, it wasn’t difficult to imagine getting to the last level, level 60 in a year and a half as advertised. I was starting to notice the vocabulary I was learning in the music I listened to, excited that so as long as I could match my current pace, I would have mastered Japanese in just over a year. How naive I had been.

The thing about spaced repetition systems, is that you’re trying to commit the Kanji and vocabulary to your long-term memory, remembering them indefinitely. So you keep reviewing again after 1 week, after 2 weeks, after 1 month, and finally, in WaniKani, after 4 months the item is considered “Burned” and you never see it again in reviews. Beyond that, ambient exposure through reading is probably enough to avoid forgetting it.

These longer-term reviews didn’t get in the way of my high accuracy rate, but the additional workload made my review sessions start to take longer and longer. By the time I was hitting my first batch of 4 month reviews, I was spending at least an hour a day on my 200ish of my lessons and reviews. To be confident that this was as hard as hard as it would get I calculated that about ~150 total vocab/radicals/kanji per WaniKani level. Some vocabulary were also starting to get fairly obscure. I’m still not exactly sure what outpatient means in English, but 外来 was one of the words I was learning in Japanese. An hour a day was a large enough time commitment that I was starting to question whether it was worth continuing.

When getting an item wrong, spaced repetition systems adjust their model of how well you know that item. WaniKani uses discrete memory stages: “Apprentice” 1-4, “Guru” 1 & 2, “Master”, “Enlightened”, and “Burned”. WaniKani places a lot of weight on how often you get an item wrong before you get it right. Getting an item wrong only once, then right on the next try because you carefully reviewed and committed the mnemonic to your short term memory, only moves an item back 2 memory stages ². This means you can get an item wrong after not having seen it in over 4 months, and then next see it again over two 2 weeks later. Just getting the item right on the first re-try isn’t enough to prove that you still know the item well enough to remember it in two weeks.

I started to dedicate less time to WaniKani, just 30-60 minutes per day instead of just over an hour. Some days I wouldn’t even finish all of my reviews, much less all of my new lessons. Consequently, I started to level up more slowly, and my accuracy started to drop. My lower accuracy further increased my workload, and I found that my accuracy on cards that I’d gotten wrong two weeks earlier stayed fairly low. Eventually I was rarely finishing all of my reviews. After traveling for two weeks, the mountain of reviews I returned to made continuing feel impossible.

After a couple of months futilely trying catch back up, my accuracy rate quickly falling, I let go completely, giving up not only on finishing WaniKani, but also achieving Japanese reading and writing proficiency.

Come back tomorrow for part 2 where I try again more intelligently.

“gh” as in cough, “o” as in “women”, and “ti” as in “nation”. ↩
The exact formula is documented in WaniKani’s knowledge base. ↩

Unformed Delta - spaced-repetition

What makes a good spaced repetition system? (WaniKani)

WaniKani