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, 大和市 charges about 405,185 yen a year while 中井町 charges about 287,235 yen — a gap of about 117,950 yen. Using the municipal rates published by Kanagawa Prefecture for the 2025 fiscal year (Reiwa 7), 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 32 out of 33 — the second most expensive (about 393,778 yen a year).
How the premium is built — and where municipalities differ
A fourth tier, the child-rearing support levy, is added from the Reiwa 8 (2026) fiscal year. This ranking uses the 2025 fiscal year (Reiwa 7) rates — the most recent prefecture-wide comparison Kanagawa Prefecture publishes — so that new tier is not included. Actual Reiwa 8 rates are set by each municipality and the prefecture's comparison table will follow.
A distinctive feature of Kanagawa Prefecture is how many municipalities levy a per-household charge: 31 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 | 287,235 yen | approx. 23,936 yen |
| 2 | 清川村 | 289,377 yen | approx. 24,115 yen |
| 3 | 葉山町 | 322,355 yen | approx. 26,863 yen |
| 4 | 大井町 | 323,014 yen | approx. 26,918 yen |
| 5 | 開成町 | 325,511 yen | approx. 27,126 yen |
| 6 | 松田町 | 326,232 yen | approx. 27,186 yen |
| 7 | 厚木市 | 327,317 yen | approx. 27,276 yen |
| 8 | 伊勢原市 | 327,406 yen | approx. 27,284 yen |
| 9 | 箱根町 | 329,464 yen | approx. 27,455 yen |
| 10 | 湯河原町 | 330,300 yen | approx. 27,525 yen |
| 11 | 真鶴町 | 330,733 yen | approx. 27,561 yen |
| 12 | 寒川町 | 330,980 yen | approx. 27,582 yen |
| 13 | 逗子市 | 334,907 yen | approx. 27,909 yen |
| 14 | 綾瀬市 | 340,690 yen | approx. 28,391 yen |
| 15 | 相模原市 | 345,586 yen | approx. 28,799 yen |
| 16 | 海老名市 | 348,964 yen | approx. 29,080 yen |
| 17 | 愛川町 | 349,978 yen | approx. 29,165 yen |
| 18 | 三浦市 | 357,681 yen | approx. 29,807 yen |
| 19 | 座間市 | 359,870 yen | approx. 29,989 yen |
| 20 | 大磯町 | 366,850 yen | approx. 30,571 yen |
| 21 | 南足柄市 | 368,866 yen | approx. 30,739 yen |
| 22 | 茅ヶ崎市 | 369,878 yen | approx. 30,823 yen |
| 23 | 二宮町 | 370,129 yen | approx. 30,844 yen |
| 24 | 川崎市 | 371,009 yen | approx. 30,917 yen |
| 25 | 小田原市 | 374,539 yen | approx. 31,212 yen |
| 26 | 藤沢市 | 375,398 yen | approx. 31,283 yen |
| 27 | 山北町※ | 381,245 yen | approx. 31,770 yen |
| 28 | 秦野市 | 382,869 yen | approx. 31,906 yen |
| 29 | 鎌倉市 | 384,388 yen | approx. 32,032 yen |
| 30 | 平塚市 | 389,978 yen | approx. 32,498 yen |
| 31 | 横須賀市 | 391,315 yen | approx. 32,610 yen |
| 32 | 横浜市 | 393,778 yen | approx. 32,815 yen |
| 33 | 大和市 | 405,185 yen | approx. 33,765 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 287,235 yen a year and 大和市 is the most expensive at about 405,185 yen — a gap of about 117,950 yen (calculated from the published the 2025 fiscal year (Reiwa 7) 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 2025 fiscal year (Reiwa 7). All figures are estimates; actual premiums are set by each municipality.