National Health Insurance is the public health coverage most foreign residents use when they are not insured through an employer — and it is one of the procedures you handle at the town hall right after registering your address. It covers about 70% of your medical costs, so understanding how to enroll and what you'll pay matters from day one. This guide explains who must join, how to sign up in Karuizawa, what it covers, and how premiums work. If you have not registered your address yet, start with How to Register Your Address in Japan (転入届).
TL;DR
- If you are not on an employer's health insurance, you must enroll in National Health Insurance (国民健康保険) at the town hall.
- Enroll within 14 days of moving in or losing other coverage — usually alongside your 転入届.
- It covers about 70% of medical costs; you pay the remaining 30% at the clinic.
- Premiums are based on last year's household income — often low for recent arrivals.
- The High-Cost Medical Expense Benefit (高額療養費) caps your out-of-pocket cost in any single month.
What is National Health Insurance (国民健康保険)?
National Health Insurance, or 国民健康保険 (kokumin kenkō hoken), is the municipally-run public health insurance for residents who are not covered by employees' health insurance. It is run by Karuizawa Town and is part of Japan's universal coverage system. With it, you pay only a portion of your medical bills, and the insurer covers the rest.
Who has to enroll?
Enrollment is mandatory for residents who are not otherwise insured. In practice:
- You enroll in National Health Insurance if you are self-employed, freelancing, studying, between jobs, retired, or otherwise not on a company plan.
- You do not enroll if your employer puts you on employees' health insurance (社会保険) — that coverage takes its place.
Foreign residents registered to stay three months or more are expected to be covered by one or the other. You cannot simply opt out.
How do I enroll in Karuizawa?
Enrollment happens at Karuizawa Town Hall, normally at the same visit as your moving-in notification (転入届). Bring:
- Residence card (在留カード) for each person enrolling.
- My Number (マイナンバー) — see The My Number Card Explained.
- Proof of when previous coverage ended — if you moved from another municipality or just left a job (e.g. a certificate of loss of employees' insurance).
- Passport.
You must enroll within 14 days of becoming eligible (moving in, or losing other insurance). Coverage is backdated to when you became eligible, so delaying does not avoid premiums.
What does it cover, and how much do I pay?
National Health Insurance covers roughly 70% of most medical and dental costs, leaving you to pay about 30% at the point of care. It applies to:
- Doctor and clinic visits, and hospital treatment.
- Prescription medicines from the pharmacy.
- Most standard dental care.
Some things — like routine check-ups, elective cosmetic procedures, and normal childbirth — are handled separately or through other subsidies. When you visit a clinic, you simply present your insurance and pay your 30% share.
How much are the premiums?
Premiums (保険料) are set by Karuizawa Town and are based mainly on:
- Your household's income from the previous year, and
- The number of people enrolled in your household.
Because premiums look back at last year's income, new arrivals with no prior Japanese income often pay very little at first, with the amount recalculated once income is on record. You receive bills you pay in installments across the year.
The High-Cost Medical Expense Benefit (高額療養費)
If you have a serious illness or a hospital stay, your 30% share could still be large. The High-Cost Medical Expense Benefit (高額療養費, kōgaku ryōyōhi) caps how much you actually pay in a single calendar month based on your income. Anything above the cap is reimbursed or, with the right certificate arranged in advance, never charged. This is the safety net that keeps a major medical event from becoming a financial crisis.
Do I get a health insurance card?
Yes — you receive a health insurance card (保険証) to show at clinics. Note that Japan is moving toward using the My Number Card as your insurance card (マイナ保険証) and is phasing out the standalone paper card, so it is worth linking your My Number Card when you enroll. See our My Number Card guide for how that works.
What if I get a job or leave Japan?
National Health Insurance does not stop on its own:
- If you start a job with employees' health insurance, you must cancel National Health Insurance at the town hall.
- If you leave Japan, cancel it and return the card.
Forgetting to cancel can lead to duplicate coverage or premium bills, so handle it as part of any change in your situation.
How ERISA helps
ERISA (有限会社えり紗) makes sure your insurance is set up correctly from the start. We accompany you to Karuizawa Town Hall, confirm whether you should be on National Health Insurance or employees' insurance, help you complete enrollment alongside your residence registration and My Number, and explain your premium bills and the high-cost cap so there are no surprises. We can also help you cancel correctly if your situation changes.
Setting up life in Karuizawa? See the Karuizawa Guide for the full first-steps checklist, or get in touch.