National Health Insurance (NHI) premiums differ sharply between municipalities within Saitama Prefecture. For the same 40-year-old living alone on ¥4 million of employment income, 所沢市 charges about 418,577 yen a year while 川島町 charges about 311,840 yen — a gap of about 106,737 yen. Using the municipal rates published by Saitama Prefecture for the 2026 fiscal year (Reiwa 8), we calculated all 63 municipalities on identical assumptions and turned the result into a ranking and a simulator. What matters most is that Saitama Prefecture has announced it will "semi-unify" these rates in the Reiwa 9 fiscal year and fully unify them in Reiwa 12. The cheaper your municipality is today, the more likely your premium is to rise.
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.
Saitama Prefecture is almost entirely a two-component system (income-based plus per-capita); only 3 municipalities add a per-household charge.
Premium simulator — all 63 municipalities at once
Enter your age, income and household, and the tool estimates your premium and ranks all 63 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 63 municipalities.
| Rank | Municipality | Annual premium (est.) | Per month |
|---|---|---|---|
| 1 | 川島町 | 311,840 yen | approx. 25,987 yen |
| 2 | 戸田市 | 318,617 yen | approx. 26,551 yen |
| 3 | 和光市 | 322,600 yen | approx. 26,883 yen |
| 4 | 神川町※ | 322,947 yen | approx. 26,912 yen |
| 5 | 越生町 | 328,670 yen | approx. 27,389 yen |
| 6 | 松伏町 | 334,398 yen | approx. 27,866 yen |
| 7 | 蕨 市 | 349,070 yen | approx. 29,089 yen |
| 8 | 杉戸町 | 355,860 yen | approx. 29,655 yen |
| 9 | 吉川市 | 357,260 yen | approx. 29,772 yen |
| 10 | 寄居町 | 358,763 yen | approx. 29,897 yen |
| 11 | 熊谷市 | 359,292 yen | approx. 29,941 yen |
| 12 | 羽生市 | 359,357 yen | approx. 29,946 yen |
| 13 | 秩父市 | 360,262 yen | approx. 30,022 yen |
| 14 | ときがわ町 | 361,184 yen | approx. 30,099 yen |
| 15 | 鳩山町 | 362,435 yen | approx. 30,203 yen |
| 16 | 北本市 | 362,748 yen | approx. 30,229 yen |
| 17 | 朝霞市※ | 363,810 yen | approx. 30,318 yen |
| 18 | 白岡市 | 364,526 yen | approx. 30,377 yen |
| 19 | 横瀬町 | 364,988 yen | approx. 30,416 yen |
| 20 | 八潮市 | 366,546 yen | approx. 30,546 yen |
| 21 | 小鹿野町 | 366,570 yen | approx. 30,548 yen |
| 22 | 新座市 | 369,771 yen | approx. 30,814 yen |
| 23 | ふじみ野市 | 369,773 yen | approx. 30,814 yen |
| 24 | 桶川市 | 371,156 yen | approx. 30,930 yen |
| 25 | 東秩父村 | 371,392 yen | approx. 30,949 yen |
| 26 | 川越市 | 372,751 yen | approx. 31,063 yen |
| 27 | 本庄市 | 374,018 yen | approx. 31,168 yen |
| 28 | 深谷市 | 374,657 yen | approx. 31,221 yen |
| 29 | 飯能市 | 375,374 yen | approx. 31,281 yen |
| 30 | 川口市 | 378,138 yen | approx. 31,512 yen |
| 31 | さいたま市 | 378,900 yen | approx. 31,575 yen |
| 32 | 長瀞町※ | 379,338 yen | approx. 31,612 yen |
| 33 | 鴻巣市 | 379,732 yen | approx. 31,644 yen |
| 34 | 美里町 | 380,209 yen | approx. 31,684 yen |
| 35 | 小川町 | 381,700 yen | approx. 31,808 yen |
| 36 | 宮代町 | 382,211 yen | approx. 31,851 yen |
| 37 | 吉見町 | 384,655 yen | approx. 32,055 yen |
| 38 | 富士見市 | 385,220 yen | approx. 32,102 yen |
| 39 | 三芳町 | 385,725 yen | approx. 32,144 yen |
| 40 | 行田市 | 388,250 yen | approx. 32,354 yen |
| 41 | 東松山市 | 388,347 yen | approx. 32,362 yen |
| 42 | 志木市 | 388,530 yen | approx. 32,378 yen |
| 43 | 加須市 | 389,374 yen | approx. 32,448 yen |
| 44 | 蓮田市 | 390,032 yen | approx. 32,503 yen |
| 45 | 幸手市 | 391,655 yen | approx. 32,638 yen |
| 46 | 三郷市 | 392,191 yen | approx. 32,683 yen |
| 47 | 毛呂山町 | 393,180 yen | approx. 32,765 yen |
| 48 | 鶴ヶ島市 | 397,550 yen | approx. 33,129 yen |
| 49 | 狭山市 | 397,585 yen | approx. 33,132 yen |
| 50 | 滑川町 | 398,140 yen | approx. 33,178 yen |
| 51 | 久喜市 | 399,481 yen | approx. 33,290 yen |
| 52 | 入間市 | 400,559 yen | approx. 33,380 yen |
| 53 | 日高市 | 400,568 yen | approx. 33,381 yen |
| 54 | 坂戸市 | 401,992 yen | approx. 33,499 yen |
| 55 | 上里町 | 403,145 yen | approx. 33,595 yen |
| 56 | 上尾市 | 403,795 yen | approx. 33,650 yen |
| 57 | 皆野町 | 404,347 yen | approx. 33,696 yen |
| 58 | 越谷市 | 404,448 yen | approx. 33,704 yen |
| 59 | 嵐山町 | 406,867 yen | approx. 33,906 yen |
| 60 | 伊奈町 | 407,169 yen | approx. 33,931 yen |
| 61 | 春日部市 | 414,357 yen | approx. 34,530 yen |
| 62 | 草加市 | 416,583 yen | approx. 34,715 yen |
| 63 | 所沢市 | 418,577 yen | approx. 34,881 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
Saitama Prefecture is pursuing unification of premium levels, aiming for "the same household composition and the same income to pay the same premium wherever you live in the prefecture". The schedule is semi-unification in Reiwa 9 and full unification in Reiwa 12. The prefecture states plainly that municipalities currently charging below the standard rate will see their rates rise — so the cheaper your municipality is today, the more likely it is to go up.
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 Saitama Prefecture has the cheapest NHI premium?
On the model case of a 40-year-old living alone with ¥4 million of employment income, 川島町 is cheapest at about 311,840 yen a year and 所沢市 is the most expensive at about 418,577 yen — a gap of about 106,737 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 Saitama Prefecture for the 2026 fiscal year (Reiwa 8). All figures are estimates; actual premiums are set by each municipality.