This isn't a "which is better" choice — for most people it's decided for you by your work situation. Mio doesn't do vibes; here's who's in which, what it costs, and where people get burned.
Japan runs a universal coverage system, and it splits into two big buckets. Employees' Health Insurance (Shakai Hoken / 健康保険) covers company employees; your workplace enrols you and handles it through payroll. National Health Insurance (Kokumin Kenko Hoken) is the residence-based scheme for the self-employed, freelancers, students, and people not employed under 75. You don't pick between them freely — your employment status decides it. If you have a full-time job, you're in Shakai Hoken; if you don't, you enrol yourself in Kokuho at the city hall.
The foreigner rule: if you have a residence status of more than 3 months and have registered your address, you're generally required to be in one of these. You can't opt out because you have foreign private insurance. If you're not covered by an employer plan, you must join Kokuho — usually within 14 days of registering your address, at the 国民健康保険課 (Kokumin Kenko Hoken-ka) counter.
This is where the two systems really differ. Shakai Hoken premiums are based on your monthly remuneration (a "standard monthly" figure), and — crucially — your employer pays about half. Your share is deducted straight from your salary, so you rarely think about it.
Kokuho premiums are calculated by your municipality from your previous year's income (plus per-person and per-household components; some areas also weigh assets). There's no employer to split it with — you pay all of it yourself, via bills or bank transfer. Premiums vary by income and by municipality, so two people can pay very different amounts. There are also reductions for low-income households — if your income is low, ask the city office; don't assume the full rate.
Whichever one you're in, the core benefit is the same. At the clinic or hospital you show your insurance card and pay only your co-payment — 30% of the cost for most adults under 70 (children and older people pay less). The other 70% is covered.
The part people underestimate is the High-Cost Medical Expense Benefit (高額療養費 / kōgaku ryōyōhi). It caps your out-of-pocket total for the month based on your age and income — for an average earner that ceiling is around ¥80,000–90,000 per month (illustrative; the exact figure depends on your income bracket and can be revised). Above the cap, the excess is reimbursed. So a serious illness or surgery does not mean a catastrophic bill. Both Shakai Hoken and Kokuho give you this protection.
| Shakai Hoken (Employees') | Kokumin Kenko Hoken (National) | |
|---|---|---|
| Who | Company employees | Freelancers, students, self-employed, unemployed |
| Where you enrol | Through your employer (automatic) | Yourself, at the city/ward office |
| Who pays | You + employer (≈ split) | You pay the whole premium |
| Premium basis | Your monthly remuneration (salary) | Last year's income + household, by municipality |
| Dependents | Family can be covered as dependents, often no extra per-head premium | Each household member enrolls; premium reflects the household |
| Patient cost share | ~30% + high-cost cap | ~30% + high-cost cap |
Exact rates, brackets, and dependent rules vary by insurer, prefecture, municipality, and year — always confirm with your employer's HR or your city office.
Enrolment is mandatory, and skipping it doesn't save money — it stores up trouble. If you leave a job and don't switch, you're supposed to move to Kokuho, and when you finally enrol, the city can bill you back-premiums for the months you were uncovered (commonly up to about two years). Meanwhile, if you get sick with no card, you pay 100% and lose the high-cost cap. There's no upside to being uninsured — only a delayed, larger bill.
Your insurance follows your employment. Join a company → employer moves you onto Shakai Hoken. Leave a company → you're no longer on their plan, so within about 14 days you either (a) get onto a new employer's Shakai Hoken, (b) enrol in Kokuho at the city office, or (c) in some cases continue your old employer plan voluntarily for a limited period ("nini keizoku"). Don't let a gap open up. When you change address between cities, tell both city offices so your Kokuho record moves with you.
Leaving Japan for good? Cancel your insurance (and check your pension) as part of departure — and if you paid into the pension system, you may be able to claim a lump-sum withdrawal. See: pension refund when leaving Japan →
Employed → Shakai Hoken (employer splits the cost). Not employed → Kokumin Kenko Hoken at the city office (you pay it all, income-based). Both cover 70% and cap your worst-case monthly bill, so the real mistake isn't picking the "wrong" one — it's being in neither. Keep continuous coverage, and switch the moment your job status changes.