This is exactly the kind of rule where not knowing costs you real money — either in panic-buying private insurance you don't need, or in fronting a scary hospital bill you never had to. Mio reads the official Japanese source and gives you the insider read.
If you're enrolled in any Japanese public health insurance, you already pay only 30% of most medical costs. Kōgaku ryōyōhi goes further: it puts a ceiling on that 30% within a single calendar month, calculated per person per medical institution and by your income bracket. Cross the ceiling and the excess is refunded (or, with a certificate, never charged). Lower income → lower cap; higher income → higher cap, but still capped.
| Income band (under-70, rough) | Approx. monthly cap |
|---|---|
| Lower income /住民税 non-taxable household | ~¥35,400 |
| Standard middle income (roughly ¥3.7–7.7M/yr) | ~¥80,000 + small income-linked add-on |
| Higher income | ~¥150,000–250,000 (rises with income) |
Illustrative only — exact brackets, formulas and the small usage-linked component are set by MHLW and change over time. Ages 70+ use a different table. Confirm your own cap with your insurer or city office.
Left alone, you'd pay the full 30% at the counter and claim the excess back later — a refund that can take weeks. Avoid that entirely:
Option A — limit certificate. Ask your insurer in advance for an Eligibility Certificate for Ceiling-Amount Application (gendogaku tekiyō nintei-shō, 限度額適用認定証). Show it at reception and the counter charge is capped on the spot.
Option B — My Number card. If your My Number card is registered as your health insurance card (maina hoken-shō), a participating hospital can read your cap directly — so you pay only the cap with no separate certificate and no yearly renewal. This is the low-effort path for most residents.
If your household qualifies for the high-cost benefit 3 or more times within the most recent 12 months, then from the 4th time your monthly cap drops to an even lower amount. So a long or repeated illness gets cheaper per month the longer it runs — the opposite of what people fear.
Many foreign residents buy private "hospitalization" insurance imagining a catastrophic, unlimited bill. But with kōgaku ryōyōhi, a covered treatment that would cost ¥1,000,000 gross doesn't cost you ¥300,000 — it costs you roughly your monthly cap (e.g. ~¥80,000 for a standard earner), and less again after the 3rd month. Before paying for private cover, do the honest math: what is it actually protecting you from that the public cap doesn't already handle? See the health insurance guide → and the arrival checklist →.
If you're in any Japanese public health insurance, you're already protected by a monthly cap. Link your My Number card as your health card (or request the limit certificate before a planned admission), and you'll never front a large sum. Then re-read any private medical insurance pitch with that cap in mind — a lot of it is covering a gap that doesn't exist.
Mio