NHI Premium Calculation
NHI premium calculation in Japan turns your prior-year income and household size into an annual municipal bill through a fixed set of portions and rating pieces.1 The same income can produce visibly different bills in different cities, and the first bill after arrival often looks deceptively low before the second-year step-up.2
Procedures, fees, and requirements can change. Confirm current details at your municipal or ward office NHI counter. This article is general information, not tax advice; for your specific case, consult a licensed tax accountant (zeirishi).
Overview
National Health Insurance (NHI) charges every enrolled household one annual premium computed from additive portions, each priced by rating pieces your municipality publishes yearly.3 How Japan's Universal-Coverage System Works maps where NHI sits among the schemes; this article stays on the arithmetic.
For fiscal year Reiwa 8 (FY2026, April 2026 to March 2027), the portions are four: medical-care, late-elderly support, long-term-care for members aged 40 to 64, and the child-care support portion newly added from Reiwa 8 (as of 2026-09-04; confirm current portions with your municipal NHI counter).3 Nakano Ward confirms the same four-part split and the Reiwa 8 start date of the child-care addition (as of 2026-06-26).4
The Portions: What the Bill Funds
The annual premium equals the medical-care portion plus the late-elderly support portion plus, for households with members aged 40 to 64, the long-term-care portion, plus the child-care support portion from Reiwa 8 onward.43 Each portion has its own rates and its own cap, so the household total is the sum of capped portion amounts.3
Medical-care portion for general care
The 基礎分 (kiso-bun, "medical-care portion") funds the medical care of NHI members themselves, and every enrolled household pays it.3 In Sapporo's FY2026 table it runs 8.61 percent of the income base plus 20,550 yen per member plus 32,540 yen per household, capped at 670,000 yen (as of 2026-09-04).3 In Nakano's FY2026 table it runs 8.03 percent plus 47,100 yen per member (23,550 yen for preschool children), with no household piece, capped at the same 670,000 yen (as of 2026-06-26).4
Late-elderly support portion for the senior system
The 支援分 (shien-bun, "late-elderly support portion") funds the medical system for residents aged 75 and over, and every NHI household pays it regardless of member ages.3 Sapporo's FY2026 figures are 2.56 percent plus 6,330 yen per member plus 10,010 yen per household, capped at 260,000 yen (as of 2026-09-04).3 Nakano's FY2026 figures are 2.94 percent plus 17,400 yen per member (8,700 yen preschool), capped at the same 260,000 yen (as of 2026-06-26).4
Long-term-care portion for ages 40 to 64
The 介護分 (kaigo-bun, "long-term-care portion") applies only where the household includes NHI members aged 40 to 64; households with no member in that band are not charged it.43 Sapporo's FY2026 figures are 2.33 percent on the income of members in the band plus 6,020 yen per band member plus 7,550 yen per household, capped at 170,000 yen (as of 2026-09-04).3 Nakano's FY2026 figures are 2.53 percent plus 17,700 yen per band member, capped at the same 170,000 yen (as of 2026-06-26).4
Members turning 40 mid-year are charged the care portion from the birthday month (the previous month if born on the 1st).43 Members turning 65 mid-year are pre-rated only through the month before the birthday month, with no mid-year rebilling for that change.4
| Portion | FY2025 (Reiwa 7) cap | FY2026 (Reiwa 8) cap | As of | Notes |
|---|---|---|---|---|
| Medical-care | 660,000 yen | 670,000 yen | 2026-09-043 | Cap per household for the portion |
| Late-elderly support | 260,000 yen | 260,000 yen | 2026-09-043 | Unchanged between the two years |
| Long-term-care (40 to 64) | 170,000 yen | 170,000 yen | 2026-09-043 | Only where a band member is enrolled |
| Child-care support (new) | none | 30,000 yen | 2026-09-043 | Added from Reiwa 8 |
The table above reflects the portion caps both cities published for FY2026, with the FY2025 national total of 1,090,000 yen (660,000 plus 260,000 plus 170,000) as the prior-year reference (as of 2026-06-10; confirm current caps with your municipal NHI counter).2 No matter how high the income, a portion never exceeds its cap, though the caps themselves move nearly every year.2
The Rating Pieces: How Each Portion Is Priced
Each portion is priced by rating pieces. The income-rated piece scales with prior-year income, the per-capita piece scales with member count, and some municipalities add a household-rated or assets-rated piece on top.43
Income-rated piece from prior-year income
The 所得割 (shotoku-wari, "income-rated piece") multiplies prior-year income minus the residence-tax basic deduction of 430,000 yen by the municipality's rate.4 Nakano defines the base, called 旧ただし書き所得 (kyu-tadashigaki shotoku, "prior-year income base"), as total income excluding retirement income minus the residence-tax basic deduction.4
Sapporo uses the same base: employment, pension, and business income totals before income deductions, plus land and building transfer income after special deduction and declared share-transfer income, while disability and survivor pensions, employment insurance, and retirement income stay out.3 Each member's income piece is computed individually and summed at household level.3
Per-capita piece per household member
The 均等割 (kintō-wari, "per-capita piece") is a flat amount per enrolled member times the member count.4 Unlike employer insurance, NHI has no dependent exemption, so every family member adds the full flat amount.2
Preschool children, meaning children under 6 on April 1, pay half the per-capita piece in both fetched tables.45 The Reiwa 8 child-care support portion, called 子ども・子育て分 (kodomo kosodate-bun, "child-care support portion"), adds a small income piece plus a small per-capita piece: Sapporo charges 0.29 percent plus 1,100 yen per member aged 18 and over plus 1,000 yen per household, capped at 30,000 yen (as of 2026-09-04).3 Nakano charges 0.27 percent plus 1,873 yen per member and fully exempts members under 18 from that per-capita piece (as of 2026-06-26).4
Assets-rated and household-rated pieces in some municipalities
The 平等割 (byōdō-wari, "household-rated piece") is a flat amount per household, used by Sapporo across all four portions but absent from Nakano's table.43 Tokyo's 23 wards follow the two-piece pattern of income plus per-capita only.24
Some municipalities outside the 23 wards retain an 資産割 (shisan-wari, "assets-rated piece") tied to property holdings. No rate table for an assets-rated piece was verified in this article's sources, so check your own city's table for whether yours uses one.
Prior-Year Income and the Residence-Tax Link
NHI premiums for a fiscal year running April to March are computed from the prior calendar year's income, the same income base that feeds residence tax.3 The Residence-Tax Year-Two Surprise walks through the parallel timing on the tax side; the premium side below follows the same lag.
Which income year feeds which premium year
FY2026 (Reiwa 8) premiums are computed from calendar-year 2025 income, as Sapporo's formula states directly.3 The annual bill is fixed in June once prior-year income is known, then collected in 10 installments from June through the following March at one-tenth each.4
Mid-year joiners are rated retroactively from the qualifying month, such as the day after company retirement or the transfer-in date, not from the filing month.43 Mid-year leavers are re-rated through the month before the leaving month.43 Transfer-in residents are first billed the basic charge of per-capita plus household pieces, then re-rated once the prior municipality reports the income.43
Low-income reductions apply automatically, but only once every member's income is known through a tax return, residence-tax return, or the NHI income declaration the city sends.5 New arrivals from abroad who cannot file a residence-tax return should complete and return that NHI declaration instead.4
Why the first bill can look low and the second bill jumps
A new arrival with no prior-year domestic income owes a near-zero income piece in year one, so the first bill sits near the per-capita and household-piece floor.432 The second-year bill reflects the first full year of declared domestic income, which produces the step-up new residents consistently report.2
Households with low income receive automatic 70, 50, or 20 percent reductions of the per-capita and household pieces once declarations are complete; the FY2026 70 percent line sits at 430,000 yen plus 100,000 yen per salary or pension earner beyond the first, judged on 2025 income (as of 2026-08-27; confirm current thresholds with your municipal NHI counter).5 Residents who lost jobs involuntarily, with employment-insurance separation codes 11, 12, 21 through 23, or 31 through 34 and age 64 or under at separation, are rated on 30/100 of prior-year salary income from the month after separation through the end of the next fiscal year.45
| Item | Figure | As of | Notes |
|---|---|---|---|
| Basic deduction from the income base | 430,000 yen | statute-based4 | Residence-tax basic deduction |
| Low-income reduction bands on per-capita and household pieces | 70%, 50%, 20% | 2026-08-275 | Automatic once income is declared |
| Preschool per-capita cut | 50% | 2026-08-275 | Applies after any low-income reduction |
| Involuntary-unemployment salary rating | 30/100 | 2026-08-275 | Separation codes 11, 12, 21-23, 31-34 |
The table above collects the relief figures a reader checks first when a bill looks wrong (as of 2026-08-27).5 None of them needs a separate application except the unemployment and childbirth cases, which require notification with the relevant certificate.5
Reading Your Municipality Rate Table
Every number in this article belongs to the city named beside it. Your bill uses your city's table, published fresh each year, and the reading method below works on any of them.43
Where the table lives and when it updates
Each municipality publishes its rates annually: Nakano sets them by ward-assembly decision around March for the April-to-March year (as of 2026-06-26).4 Sapporo finalizes its calculation rates in early June and publishes a web trial-calculation tool alongside the table (as of 2026-09-04).3 Hokkaido plans a single prefecture-wide rate schedule from Reiwa 12 (2030), after which identical households pay identically anywhere in the prefecture (as of 2026-09-04).3
Tokyo 23 wards pattern: income plus per-capita only
Nakano's published table lists only the income piece plus the per-capita piece for every portion, with preschool halving and no household or assets piece.4 A Shinjuku FY2026 calculator shows the same two-piece shape with different numbers, medical 7.51 percent plus 47,600 yen per member, support 2.80 percent plus 17,600 yen, care 2.21 percent plus 17,400 yen (as of 2026; page undated, verified on fetch).6
A worked reading example without quoting a universal rate
The reading method runs per portion: multiply prior-year income minus 430,000 yen by the income rate, add the per-capita amount times the member count plus any household piece, truncate per the city rule, then apply the portion cap.43 Applied to Nakano's Reiwa 8 table for a single member under 40 with a 2,000,000 yen income base: medical is (2,000,000 minus 430,000) times 8.03 percent, about 126,000 yen, plus 47,100 yen per-capita, about 173,000 yen; support is the same base times 2.94 percent, about 46,100 yen, plus 17,400 yen, about 63,500 yen; the household total lands near 236,500 yen before the city's truncation rule (as of 2026-06-26).4 Treat the result as a demonstration of the method on Nakano's table, never as a national figure.
Why the Same Income Produces Different Bills
Rate tables, flat amounts, and the presence of a household piece are all municipal choices, so identical incomes produce different household bills across Japan.43
Rate and flat-amount differences by municipality
The fetched FY2026 tables show the mechanism directly: medical income rates of 8.03 percent in Nakano versus 8.61 percent in Sapporo, and medical per-capita amounts of 47,100 yen versus 20,550 yen, with Sapporo adding a 32,540 yen household piece Nakano lacks (as of 2026-09-04).43 Professional guidance characterizes the spread as tens of thousands to over 100,000 yen a year at the same income.2
Household size and age-mix effects
Per-capita multiplication means each additional member adds the full flat amount, for example 47,100 yen in medical per-capita per extra member on Nakano's table.42 A household with a member aged 40 to 64 adds the entire care portion, while a same-income household with all members under 40 pays none of it.43
Good to know
The bill goes to the household head
The premium payer is the household head, even where the head carries other coverage and only other members hold NHI.7 The notice arrives in mid-June, and late payment can draw a surcharge, so the head should confirm the bill even when the amount concerns other members.7 A head enrolled in employer insurance while family members hold NHI still receives the NHI notice for those members, with the head's own income counted in any reduction test.57
Ten installments from June, not twelve monthly bills
The April-to-March annual premium is collected in 10 installments from June through the following March.4 Losing NHI mid-year does not erase remaining installments, because they collect the already-fixed annual bill through the month before the leaving month.4
A move across municipal lines resets the table you use
Transfer-in residents are first billed the basic charge, then re-rated after the income inquiry to the prior municipality, with a fresh notice on any change.43 Completing the old ward's de-registration and the new ward's enrollment keeps the record continuous.
The cap bounds the bill but the cap itself moves yearly
Portion caps rose between Reiwa 7 and Reiwa 8, with medical moving from 660,000 to 670,000 yen and the new child-care portion adding a 30,000 yen cap (as of 2026-09-04).432 High earners hit the caps while middle earners feel the rate changes, so a capped bill this year does not promise the same ceiling next year.2
See also
- How Japan's Universal-Coverage System Works
- The Residence-Tax Year-Two Surprise
- Health Insurance and Pension for Freelancers
- NHI Enrollment at the Ward Office
- First-Year NHI Reduction for New Arrivals
- NHI Premium Reductions and Exemptions