When is a Leech a Leech? (and how to deal with them?)

A question for more experienced Durtles, or other people who have an opinion: from when on do you consider a leech a leech?

At what point does it change from an item you’ve got a little difficulty with to being an item which needs special study?

Basically, i’m trying to determine if and when i should start doing leech-training sessions, and by what criteria i should select items to train.

I’d appreciate any advice you all have to give ^^


For me, it’s when I realize I actually dread seeing it in my reviews. That’s the moment where I’m beyond any hope of getting it right. I don’t personally tend to do any leech-specific training though, I just re-learn them in or at the end of the review session.

Usually it’s one of two problems. Either I get the meaning wrong, confusing it with a similar word with a slightly different (but important) meaning, or I confuse a kanji for a visually similar kanji. If it’s the first one I’ll check the word I’m confusing it with and create new mnemonics for both that make it impossible to mix them up, and if it’s the kanji, pulling them both up side by side and focussing on what the difference is usually helps.


Leech related scripts such as Item Inspector and the Additional Filters use a formula to determine when an item is a leech. You can deal with leeches by performing extra-studying with scripts.

  • Item Inspector will identify the leeches with the formula. You may go over your leeches reciting meanings and readings. The you move your mouse over the item to show the correct answer in a popup.

  • Self Study Quiz will quiz you on your leeches. You need the Additional Filters script to have a leech filter in Self Study Quiz to be quizzed on the leeches. You may also start Self Study Quiz from Item Inspector to be quizzed on the same leeches you have studied in Item Inspector.

  • Leech Trainer is another quiz script for leeches. It has several features targeted specifically for leeches like the insertion of visually similar items to test your understanding of leeches. I suppose it uses the same leech formula as the other two scripts but I did not verify this.

The leech formula is:

LeechValue = IncorrectCount / currentStreak1.5

The higher the value the more troublesome the item is. If you have many reviews incorrect the numerator will increase. The more often you are incorrect the higher the leech value will get. On the other hand if you are on a roll and have a streak of successful reviews the denominator will increase. The longer the streak the lower the leech value will be. If you fail a review your streak will stop and the leech value will revert to a high number.

Wanikani statistics used in the leech formula start counting streaks at 1. When you just have failed a review the streak is 1, not 0. Moreover the calculation is done separately for meanings and readings. The largest of the two numbers is the leech value.

The best parameter for the leech formula is 1. All items with a leech value greater or equal to 1 will be displayed. This will include all items that have failed a review for the first time because these items always have a leech value of 1. If you feel you should exclude these items use 1.01 for the filter parameter. Values lower than 1 will return items that are not troublesome and should not be used. Another useful value is 2. This number ensures an item is considered a leech only when you have failed it at least twice. It is also more selective as what is a leech than 1.01.


I agree with @prouleau that it’s best to just install some scripts to keep track of which items you fail the most in reviews. There are just too many to do this manually, though some people do keep lists.

But, essentially a leech is any item that you’ve failed enough times that it keeps bouncing between guru and apprentice and is not moving forward. Or you’re not able to get it to guru.

Once the item again starts to progress the question is when to consider the problem solved?

I guess, it’s up to you. I know I can still fail leeches even if they reach Enlightenment. Though, mostly, at that point they do burn.

I feel like the chances of finally burning a true leech reflects upon how well I leech trained the item. Less work=less chance of retaining it after all.


Sorry to bump an old thread. Just wondering if you’ve started to try any leech-training scripts? If yes, do you find yourself improving at lessening the leeches? And if you’ve decided not to use them, I’d love to hear your reasoning as well. Thanks in advance! ^o^/"

I’m glad you bumped the thread because it was helpful to me to learn about how the leech formula works. I use the scripts mentioned above and find them useful!

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i’ve not done any leech training. i’ve had some considerable rl issues come up, and just not been able to do all that much japanese.

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Thank you for your time answering despite your rl situation. I’m sure you’ll be able to come back again whenever you can or want to. Good thing that you have a Lifetime account! Wishing you all the best.

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