Japan’s National Health Insurance Bill Explained: Income, Household Size, and Location

2026年8月24日

Japan’s National Health Insurance Bill Explained: Income, Household Size, and Location

Your National Health Insurance premium is not a fixed national price. Your municipality calculates it for the household, mainly using each enrolled member’s income from the previous calendar year, the number and ages of enrolled members, and local rates for the current fiscal year.

This guide is for foreign residents who are self-employed, studying, between jobs, or otherwise not covered by workplace health insurance. It is also useful when leaving an employer’s plan, moving between municipalities, or adding a family member.

The essentials

Premiums normally cover the fiscal year from April through the following March.
The calculation usually has medical, older-person support, and—at ages 40 to 64—long-term care portions.
Each portion generally combines an income-based charge and a per-person charge.
Rates, annual limits, payment schedules, and some relief programs vary by municipality.
A low current income does not necessarily mean a low bill immediately because the calculation mainly looks at the previous year.

TOC

First confirm whether National Health Insurance is your system

National Health Insurance, commonly called NHI or Kokuho, is mainly for registered residents who are not insured through an employer or another public medical insurance system.

Typical members include:

self-employed residents and freelancers;
students without qualifying workplace coverage;
unemployed residents;
part-time workers who are not enrolled in an employer’s health insurance;
family members who cannot be registered as dependents under another public plan.

Foreign nationality does not by itself change the premium formula. Registered foreign residents who meet the residence requirements generally enter the same municipal system as other eligible residents.

However, NHI is not automatically the right plan for everyone. You will generally not enroll if you:

already have health insurance through an employer;
qualify as a dependent under a family member’s workplace plan;
receive public assistance that places you outside NHI;
have entered the medical system for people aged 75 or older;
hold a status or period of stay that is excluded under the applicable rules.

Eligibility can depend on your residence record, status of residence, expected period in Japan, employer, and family situation. Ask the NHI counter at your city or ward office if your case is unclear.

The basic calculation: three portions added together

The clearest way to understand the bill is to treat it as up to three separate calculations. Your municipality calculates the applicable portions and adds them to produce the household’s annual premium.

1. Medical-care portion

This finances the main NHI medical-benefit system. It normally applies to every NHI member in the household.

2. Support portion for older people’s medical care

This helps finance the separate medical system serving older residents. Despite the name, it is generally included in the premium for NHI members below age 75; it is not charged only to households containing an older person.

3. Long-term care portion

This applies to NHI members who are 40 through 64 years old. A household with two enrolled adults aged 35 and 42, for example, would normally have a long-term care charge for the 42-year-old but not the 35-year-old.

At age 65, long-term care insurance moves to a different premium arrangement administered by the municipality. At age 75, most residents move from NHI to the medical system for older senior citizens.

ここがポイント: Two households with the same total income can receive different bills when they have different numbers of NHI members, different ages, or addresses in different municipalities.

What goes into each portion

Most municipal formulas combine a charge linked to income with a charge linked to the number of enrolled people. Some municipalities may also use an additional household-based component.

Income-based amount

The income-based amount is often called the shotokuwari. A simplified version looks like this:

Premium calculation income × the municipality’s income rate

For many types of income, the calculation starts with the previous calendar year’s total income and applies the deduction used by the municipality’s NHI formula. This is not simply your gross salary, bank balance, or current monthly pay.

The underlying income can include relevant categories such as:

salary income after the employment-income deduction;
business or freelance income after allowable expenses;
pension income after the applicable pension deduction;
certain other taxable income reported in Japan.

The exact tax data and deductions used can be technical. If you have overseas income, investment income, a business loss, or income earned before moving to Japan, ask the municipality how it should be reported and whether it enters the NHI calculation.

Per-person amount

The per-person amount is usually called the kintowari. It is a fixed annual charge for each person enrolled in NHI, although the amount differs by municipality and by premium portion.

This is why adding a spouse or child can increase the household bill even if that person earns no income. Children are counted as insured members, although statutory reductions apply to the per-person charge for preschool-age children.

Possible household-based amount

Some municipal systems may include a fixed amount assessed per household, often called the byodowari. Other municipalities do not use it.

The Ministry of Health, Labour and Welfare explains that municipal NHI premiums are calculated by household from ability-to-pay and benefit-related components, while the precise method is set under local rules. A formula copied from another city may therefore give the wrong result.

A practical household example

Calculate by person first, then combine the results at household level.

Consider a household with:

one 45-year-old freelancer with previous-year income;
one 38-year-old spouse with no income;
one school-age child;
all three enrolled in NHI.

The calculation would generally work like this:

Calculate the freelancer’s income-based medical and support amounts.
Add income-based long-term care because the freelancer is 45.
Calculate any income-based amounts applicable to the spouse and child; with no relevant income, these may be zero.
Add medical and support per-person charges for all three members.
Add the long-term care per-person charge only for the 45-year-old.
Apply any qualifying low-income or child-related reductions.
Apply the statutory annual ceiling separately as required for each portion.

This example shows why multiplying household income by one percentage is not enough. The number of members and their ages affect the result too.

Why the bill uses last year’s income

The annual premium generally follows income from January through December of the previous year, not what you are earning today.

For example, the premium for a fiscal year beginning in April is generally based on income from the preceding calendar year. Municipalities commonly finalize or notify the year’s amount after the relevant income information becomes available; Yokohama, for example, explains that its annual amount is decided in June.

This timing creates several situations that surprise new residents.

You recently lost your job

A person who had a strong salary last year but is unemployed now may still receive a substantial NHI bill. Do not assume the office has made a mistake.

Ask promptly about:

reductions for qualifying involuntary job loss;
municipal hardship reductions or exemptions;
payment consultation or deferral;
whether continued coverage under the former employer’s plan is available and more economical.

These options have different eligibility rules and application deadlines.

You have just moved to Japan

Your municipality may initially lack the income data needed to calculate the correct amount. It may issue a provisional bill and revise it later, or request an income declaration.

Do not treat “no Japanese income record” as meaning “no premium.” Submit every requested declaration, including a declaration of zero income when required. Without it, the municipality may be unable to apply income-based reductions.

Your income changed during the year

A new job or pay raise does not always change the income-based amount immediately. It will normally affect a later fiscal year after that income appears in the relevant calendar-year record.

Changes in NHI membership are different. Adding or removing an enrolled person can trigger a recalculation during the current year.

Low-income reductions and other relief

Several forms of relief exist, but they do not all work automatically.

Statutory reductions for low-income households

National rules provide reductions of 70%, 50%, or 20% to qualifying per-person and household-based components. Eligibility is judged using household income and other statutory conditions.

The income of the household head may matter in this test even if that person is not personally enrolled in NHI. This is one reason the notice may not match a calculation based only on the enrolled member’s pay.

A household still needs to report income correctly. A student, homemaker, or newly arrived resident with no taxable income may be asked to submit a resident-tax or NHI income declaration so the municipality can test eligibility.

Reduction for preschool-age children

The per-person component for an enrolled preschool-age child is reduced by 50% under the national measure. A household already receiving a low-income reduction can receive the child measure after the applicable calculation, rather than choosing only one of the two.

Relief for childbirth, disaster, or financial hardship

Other relief may be available in cases such as:

income loss after dismissal or business closure;
disaster damage;
severe difficulty paying;
the pre- and post-childbirth period for an eligible insured person;
special circumstances defined by the municipality.

Applications may require evidence and may not operate retroactively without limit. Contact the office before ignoring a payment deadline.

Enrollment dates, backdated premiums, and deadlines

Late paperwork usually does not erase the period when you should have been insured.

Municipal guidance commonly requires enrollment or withdrawal notification within 14 days after events such as:

moving into the municipality;
losing workplace health insurance;
joining workplace health insurance;
moving out;
leaving Japan;
the birth of a child.

If you enroll late, eligibility and premiums can be backdated to the date you should have joined—not merely the day you filed the form. Yokohama’s English guidance likewise states that premiums begin from the month a person became insured.

If you start workplace insurance, NHI does not necessarily cancel itself. Notify the municipality and show proof of the new coverage. Otherwise, NHI bills may continue even though you should no longer be enrolled.

What to prepare for the municipal office

Bring evidence of the event that starts or ends your NHI eligibility. Exact requirements and online options differ locally.

Commonly requested items include:

residence card or another accepted identity document;
My Number card or documents confirming your Individual Number;
proof of address or moving notification, where applicable;
certificate showing loss of workplace health-insurance eligibility;
proof of new workplace coverage when leaving NHI;
income information or a requested income declaration;
bank details if applying for account transfer;
authorization if someone outside the registered household acts for you.

A resignation letter may not always contain enough information to prove the exact loss-of-coverage date. Ask the former employer or insurer for a formal certificate if the municipality requires one.

Why your municipality matters

National law provides the framework, but your city or ward publishes the rates and sends the bill.

Local differences can include:

income-based percentage rates;
annual per-person amounts;
use of a household-based charge;
annual premium ceilings within the national framework;
number and timing of installments;
available payment methods;
local reduction and hardship procedures.

Moving from one city to another can therefore change the premium even when your income and household remain the same. The old municipality calculates through the applicable period before the move, and the new municipality calculates from the applicable period after enrollment there. Adjusted notices may arrive later.

For an estimate, search the official website of your city or ward for the current fiscal year plus “National Health Insurance premium calculation” or ask the NHI counter for a trial calculation. Use the correct year’s rates; an older online calculator can produce a misleading result.

Common mistakes that lead to unexpected bills

Most avoidable problems come from missing notifications or incomplete income reporting.

Assuming an employer will cancel NHI: The resident normally must notify the municipality after joining workplace insurance.
Comparing NHI with an employee’s payslip percentage: Workplace health-insurance premiums use a different system and are normally shared with the employer. NHI has no employer contribution.
Using current income instead of previous-year income: This makes estimates especially inaccurate after unemployment or a move to Japan.
Leaving a zero-income family member undeclared: The missing declaration may prevent a low-income reduction from being assessed.
Counting every household resident as an NHI member: Someone insured through an employer is not charged the NHI per-person amount, although the household head’s income can matter for certain reduction tests.
Forgetting the age-40 change: The long-term care portion can begin when an enrolled person reaches the applicable age.
Ignoring a notice because the amount seems wrong: Ask for a calculation breakdown and correction. Unpaid premiums can lead to collection action and complications with insurance administration.

How to check your own notice

A useful review takes five checks, not a full reconstruction of the municipal formula.

Confirm the coverage period and municipality.
Check which household members are listed as NHI members.
Verify whether the income year is the correct previous calendar year.
Check whether long-term care charges appear only for members in the applicable age group.
Look for reductions, revised assessments, and payment deadlines.

If something appears wrong, take the notice, income documents, and proof of any insurance or household change to the municipal NHI counter. Ask for the breakdown by medical, support, and long-term care portions.

What to check as of August 2026

Use the fiscal-year notice issued by your own municipality as the final source for current rates. National ceilings, reduction thresholds, and local rates can change from one fiscal year to the next.

Before making a budget, confirm:

the rates and fixed amounts for the fiscal year covering your dates;
whether your municipality has received your previous-year income data;
whether every household member has filed any required income declaration;
whether a job loss, birth, move, or new workplace plan requires an application;
when a recalculated notice will be issued.

The practical takeaway is simple: estimate with last year’s income, count only NHI members, add the age-based long-term care portion, and then check local reductions and rates. If your job or household changes, report it within 14 days rather than waiting for the next bill.

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