National Health Insurance (NHI) premiums differ sharply between municipalities within Kanagawa Prefecture. For the same 40-year-old living alone on ¥4 million of employment income, 秦野市 charges about 422,274 yen a year while 中井町 charges about 294,929 yen — a gap of about 127,345 yen. Using the municipal rates published by Kanagawa Prefecture for the 2026 fiscal year (Reiwa 8), we calculated all 33 municipalities on identical assumptions and turned the result into a ranking and a simulator. Yokohama, home to one in three residents of the prefecture, ranks 27 out of 33 — the 7th most expensive (about 401,449 yen a year).
How the premium is built — and where municipalities differ
A fourth tier, the child-rearing support levy, was added in the Reiwa 8 fiscal year. Its per-capita charge applies only to members aged 18 and over; the share for children under 18 is waived in full.
A distinctive feature of Kanagawa Prefecture is how many municipalities levy a per-household charge: 30 of 33 do, which makes single-person households relatively worse off.
Premium simulator — all 33 municipalities at once
Enter your age, income and household, and the tool estimates your premium and ranks all 33 municipalities at the same time.
| Rank | Municipality | Annual premium (est.) | Per month |
|---|
* Estimates. The income-based portion is calculated by applying the rate to "total income for the previous year minus the ¥430,000 basic deduction"; the per-capita and per-household levies reflect the statutory reductions (70%, 50%, 20%) and the half-rate per-capita levy for preschool children. Municipality-specific reductions, monthly pro-rating and rounding are not reflected. Always confirm the exact amount with your municipality.
Ranking: a 40-year-old living alone on ¥4 million of employment income
As a common yardstick, here is the annual premium for a 40-year-old living alone with ¥4,000,000 of employment income (¥2,760,000 of employment income after the deduction) across all 33 municipalities.
| Rank | Municipality | Annual premium (est.) | Per month |
|---|---|---|---|
| 1 | 中井町 | 294,929 yen | approx. 24,577 yen |
| 2 | 清川村 | 307,523 yen | approx. 25,627 yen |
| 3 | 箱根町 | 327,126 yen | approx. 27,260 yen |
| 4 | 大井町 | 331,205 yen | approx. 27,600 yen |
| 5 | 葉山町 | 331,345 yen | approx. 27,612 yen |
| 6 | 真鶴町 | 338,964 yen | approx. 28,247 yen |
| 7 | 厚木市 | 345,094 yen | approx. 28,758 yen |
| 8 | 綾瀬市 | 349,447 yen | approx. 29,121 yen |
| 9 | 寒川町 | 357,533 yen | approx. 29,794 yen |
| 10 | 海老名市 | 358,287 yen | approx. 29,857 yen |
| 11 | 開成町 | 358,962 yen | approx. 29,914 yen |
| 12 | 愛川町 | 362,197 yen | approx. 30,183 yen |
| 13 | 伊勢原市 | 363,461 yen | approx. 30,288 yen |
| 14 | 逗子市 | 365,248 yen | approx. 30,437 yen |
| 15 | 相模原市 | 368,289 yen | approx. 30,691 yen |
| 16 | 大磯町 | 372,710 yen | approx. 31,059 yen |
| 17 | 松田町 | 374,084 yen | approx. 31,174 yen |
| 18 | 二宮町 | 376,422 yen | approx. 31,368 yen |
| 19 | 茅ヶ崎市 | 378,057 yen | approx. 31,505 yen |
| 20 | 湯河原町 | 382,270 yen | approx. 31,856 yen |
| 21 | 藤沢市 | 384,197 yen | approx. 32,016 yen |
| 22 | 小田原市 | 386,990 yen | approx. 32,249 yen |
| 23 | 三浦市 | 392,054 yen | approx. 32,671 yen |
| 24 | 座間市 | 392,160 yen | approx. 32,680 yen |
| 25 | 鎌倉市 | 396,570 yen | approx. 33,048 yen |
| 26 | 南足柄市 | 401,446 yen | approx. 33,454 yen |
| 27 | 横浜市 | 401,449 yen | approx. 33,454 yen |
| 28 | 川崎市 | 405,599 yen | approx. 33,800 yen |
| 29 | 山北町 | 410,297 yen | approx. 34,191 yen |
| 30 | 横須賀市 | 412,812 yen | approx. 34,401 yen |
| 31 | 大和市 | 413,403 yen | approx. 34,450 yen |
| 32 | 平塚市 | 415,459 yen | approx. 34,622 yen |
| 33 | 秦野市 | 422,274 yen | approx. 35,190 yen |
Why the gap is so large within one prefecture
- The scale of discretionary transfers from the general account — municipalities top up the NHI account with local tax money to hold premiums down, in very different amounts
- Members' income levels, age mix and medical spending — areas with more older residents or higher medical costs need more revenue
- The levy structure — whether a per-household charge or an asset-based charge is used changes the burden on single-person and home-owning households
Nationally, discretionary transfers are being phased out and premium levels are being unified within each prefecture. Kanagawa Prefecture has already published its Reiwa 8 standard rates, so even today's cheaper municipalities may rise in stages.
Practical notes: moving, leaving a job, and reductions
- Premiums are pro-rated monthly by the municipality where your residence record sits. When you move, the new municipality's rates apply from the month you move in, and the old one settles up on a monthly basis (you must file within 14 days). Mid-year moves do not mean paying twice.
- None of this applies while you are on an employer's health insurance — but you hit it the moment you leave a job and join the NHI. Premiums right after leaving are based on the previous year's income and can be steep, so compare voluntary continuation, the NHI, and joining a family member's coverage.
- The 70%, 50% and 20% reductions require no application, but every member of the household must have filed their income. Even with no income, failing to file a residence tax return can cost you the reduction.
- Do not choose where to live on premiums alone. Housing costs, commuting and childcare support matter more.
Frequently asked questions
Which municipality in Kanagawa Prefecture has the cheapest NHI premium?
On the model case of a 40-year-old living alone with ¥4 million of employment income, 中井町 is cheapest at about 294,929 yen a year and 秦野市 is the most expensive at about 422,274 yen — a gap of about 127,345 yen (calculated from the published the 2026 fiscal year (Reiwa 8) rates). Rankings shift with age, income and household size, so use the simulator above for your own case.
Why do premiums differ between municipalities?
The benefits are identical nationwide, but municipalities differ in the scale of their discretionary transfers from the general account, in members' income and age mix, in medical spending, and in the levy structure. Discretionary transfers are being phased out, so cheaper municipalities may rise.
When does my premium change after I move?
From the month you move in, calculated pro rata, with the previous municipality settling up on the same basis. File within 14 days; a mid-year move does not mean paying twice.
Sources
This ranking was calculated by this site on identical assumptions from the municipal NHI rates published by Kanagawa Prefecture for the 2026 fiscal year (Reiwa 8). All figures are estimates; actual premiums are set by each municipality.
