National Health Insurance (NHI) premiums differ sharply between municipalities within Chiba Prefecture. For the same 40-year-old living alone on ¥4 million of employment income, 睦沢町 charges about 427,830 yen a year while 御宿町 charges about 288,350 yen — a gap of about 139,480 yen. Using the municipal rates published by Chiba Prefecture for the 2025 fiscal year (Reiwa 7), we calculated all 54 municipalities on identical assumptions and turned the result into a ranking and a simulator. The government-designated city of Chiba ranks 46 (about 373,075 yen a year), while neighbouring Funabashi ranks 5 (about 310,105 yen) — a gap of about 62,970 yen a year within the same commuter belt.
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 Chiba 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 Chiba Prefecture is how many municipalities levy a per-household charge: 52 of 54 do, which makes single-person households relatively worse off.
Premium simulator — all 54 municipalities at once
Enter your age, income and household, and the tool estimates your premium and ranks all 54 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 54 municipalities.
| Rank | Municipality | Annual premium (est.) | Per month |
|---|---|---|---|
| 1 | 御宿町 | 288,350 yen | approx. 24,029 yen |
| 2 | 東庄町 | 294,350 yen | approx. 24,529 yen |
| 3 | 富里市 | 300,500 yen | approx. 25,042 yen |
| 4 | 匝瑳市 | 309,990 yen | approx. 25,832 yen |
| 5 | 船橋市 | 310,105 yen | approx. 25,842 yen |
| 6 | 成田市 | 315,143 yen | approx. 26,262 yen |
| 7 | 佐倉市 | 317,450 yen | approx. 26,454 yen |
| 8 | 白井市 | 318,115 yen | approx. 26,510 yen |
| 9 | 旭市 | 319,980 yen | approx. 26,665 yen |
| 10 | 市川市 | 321,585 yen | approx. 26,799 yen |
| 11 | 横芝光町 | 322,310 yen | approx. 26,859 yen |
| 12 | 山武市 | 322,639 yen | approx. 26,887 yen |
| 13 | いすみ市 | 323,970 yen | approx. 26,998 yen |
| 14 | 九十九里町 | 325,290 yen | approx. 27,108 yen |
| 15 | 八千代市 | 325,992 yen | approx. 27,166 yen |
| 16 | 野田市 | 326,209 yen | approx. 27,184 yen |
| 17 | 栄町 | 326,606 yen | approx. 27,217 yen |
| 18 | 浦安市 | 327,498 yen | approx. 27,292 yen |
| 19 | 神崎町 | 328,960 yen | approx. 27,413 yen |
| 20 | 君津市 | 332,455 yen | approx. 27,705 yen |
| 21 | 多古町 | 333,290 yen | approx. 27,774 yen |
| 22 | 八街市 | 333,300 yen | approx. 27,775 yen |
| 23 | 鋸南町 | 338,035 yen | approx. 28,170 yen |
| 24 | 富津市 | 338,610 yen | approx. 28,218 yen |
| 25 | 長生村 | 341,365 yen | approx. 28,447 yen |
| 26 | 木更津市 | 341,911 yen | approx. 28,493 yen |
| 27 | 流山市 | 342,729 yen | approx. 28,561 yen |
| 28 | 印西市 | 346,450 yen | approx. 28,871 yen |
| 29 | 松戸市 | 346,765 yen | approx. 28,897 yen |
| 30 | 長柄町 | 347,600 yen | approx. 28,967 yen |
| 31 | 茂原市 | 347,930 yen | approx. 28,994 yen |
| 32 | 柏市 | 349,591 yen | approx. 29,133 yen |
| 33 | 勝浦市 | 355,730 yen | approx. 29,644 yen |
| 34 | 鎌ケ谷市 | 355,886 yen | approx. 29,657 yen |
| 35 | 一宮町 | 356,250 yen | approx. 29,688 yen |
| 36 | 南房総市 | 360,638 yen | approx. 30,053 yen |
| 37 | 東金市 | 364,250 yen | approx. 30,354 yen |
| 38 | 白子町 | 364,900 yen | approx. 30,408 yen |
| 39 | 袖ケ浦市 | 365,250 yen | approx. 30,438 yen |
| 40 | 大網白里市 | 367,086 yen | approx. 30,590 yen |
| 41 | 鴨川市 | 368,324 yen | approx. 30,694 yen |
| 42 | 芝山町 | 368,330 yen | approx. 30,694 yen |
| 43 | 四街道市 | 369,119 yen | approx. 30,760 yen |
| 44 | 銚子市 | 370,425 yen | approx. 30,869 yen |
| 45 | 館山市 | 372,747 yen | approx. 31,062 yen |
| 46 | 千葉市 | 373,075 yen | approx. 31,090 yen |
| 47 | 長南町 | 373,900 yen | approx. 31,158 yen |
| 48 | 酒々井町 | 377,123 yen | approx. 31,427 yen |
| 49 | 習志野市 | 378,790 yen | approx. 31,566 yen |
| 50 | 香取市 | 379,240 yen | approx. 31,603 yen |
| 51 | 市原市 | 379,602 yen | approx. 31,634 yen |
| 52 | 我孫子市 | 390,155 yen | approx. 32,513 yen |
| 53 | 大多喜町 | 391,320 yen | approx. 32,610 yen |
| 54 | 睦沢町 | 427,830 yen | approx. 35,652 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. Chiba 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 Chiba Prefecture has the cheapest NHI premium?
On the model case of a 40-year-old living alone with ¥4 million of employment income, 御宿町 is cheapest at about 288,350 yen a year and 睦沢町 is the most expensive at about 427,830 yen — a gap of about 139,480 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 Chiba Prefecture for the 2025 fiscal year (Reiwa 7). All figures are estimates; actual premiums are set by each municipality.