Joe Tomei here. This came in another email list and I thought it would be worth passing on.

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Medical Insurance -- when to schedule operations
I have found out that it is very important as to when you schedule a
major medical procedure here if you are using the National Health
Insurance (NHI). I just had both knees worked on -- a 90 man procedure that cost me 16 man because I had it done at the end of the month. If I had had it done at the beginning of the month, it probably would have
cost 10 man. Why?

Each of us under the 30-70 rule pays 30% up until a cap that is
determined by our current income. Each of us on this list probably has a different cap. When the cap is reached for that month, the 30% becomes 1% for all additional charges and NHI or the Prefecture pick up the balance. NHI does this on a monthly calendar basis so it costs more if your hospitalization/treatment goes into a second calendar month.