The largest deduction on a Japanese payslip is not tax, it is shakai hoken, and it is calculated in a way that surprises almost everyone: premiums are not a percentage of your actual salary but of your hyojun hoshu getsugaku, a standard monthly remuneration grade assigned to you once a year. Your April, May, and June pay is averaged in the teiji kettei annual review, mapped to a grade, and that grade then fixes your premiums from September until the following August regardless of what you actually earn in the intervening months. A grade change mid-year only happens through zuiji kaitei, triggered by a substantial and sustained change in fixed pay. Overtime worked in the April to June window therefore raises your premiums for the entire following year, which is a well-known quirk of Japanese payroll. On top of shakai hoken sits gensen choshu, monthly income tax withholding reconciled by the employer in December, and juminzei, which lags a full year behind the income it is based on. This calculator separates all three.

Key Regulatory Parameters & Frameworks (YA 2026)

Rule 01

Standard Monthly Remuneration Grades

Health insurance premiums are set against roughly fifty remuneration grades and employees' pension premiums against a shorter grade table with a lower upper limit. Your grade is fixed each year in the teiji kettei review using average pay for April, May, and June, applying from September for twelve months, with a zuiji kaitei revision only where fixed remuneration changes substantially and persists for three months. Bonuses are charged separately on standard bonus amounts, subject to their own per-payment and annual caps.

Rule 02

Health Insurance and Nursing Care Premiums

Employees of small and medium employers are insured through Kyokai Kenpo, where the health insurance rate is set prefecture by prefecture and sits broadly around 10% of standard monthly remuneration, split equally between employer and employee, so roughly 5% each. Large employers often run their own kenpo kumiai with their own rate. Employees aged 40 to 64 pay an additional kaigo hoken nursing care insurance premium of roughly 1.6% combined, again split in half, which appears as a separate line from the month you turn 40.

Rule 03

Employees' Pension and Employment Insurance

Kosei nenkin, the employees' pension, is charged at a nationally fixed 18.3% of standard monthly remuneration, split equally, so 9.15% falls on the employee, subject to the grade table's upper limit. Koyo hoken, employment insurance, takes a much smaller share from the employee, in the region of half a percentage point for general businesses with a higher employer share, and the rates are reviewed annually. Together these fund unemployment benefit, parental leave benefit, and the earnings-related pension.

Rule 04

The Employment Income Deduction Shapes Taxable Pay

Salaried employees deduct a statutory kyuyo shotoku kojo rather than actual expenses. It is scaled to salary with a floor for low earnings and a cap at the high-income tier, historically JPY 1,950,000 of deduction once salary reaches JPY 8,500,000. For a salary in the JPY 6.6 million to JPY 8.5 million range it has been computed as 10% of salary plus JPY 110,000. Both this figure and the basic deduction have moved in recent reform packages, so a payroll estimate built on last year's table will drift.

Rule 05

Gensen Choshu and the December Nenmatsu Chosei

Employers withhold monthly income tax using the National Tax Agency's withholding tables, which take account of the number of dependants you declare on the fuyo kojo shinkokusho. In December the employer performs nenmatsu chosei, reconciling the year's withholding against the true liability after the employment income deduction, social insurance premium deduction, basic deduction, spouse and dependant deductions, life and earthquake insurance deductions, and the housing loan credit from its second year onward. Most employees therefore receive a refund or a small extra deduction in December and never file a return.

Example Calculation: Tokyo Corporate Worker

Scenario Context: Tokyo resident aged under 40 earning JPY 7,000,000 gross annually, single with no dependants, enrolled in Kyokai Kenpo and kosei nenkin, using the long-standing basic deduction figure.

Calculation Stage	Computed Value
Annual gross salary	JPY 7,000,000
Employee shakai hoken at roughly 15% of standard remuneration	Approximately JPY 1,050,000, covering health insurance, kosei nenkin, and koyo hoken
Less employment income deduction (10% of salary plus JPY 110,000)	JPY 810,000, giving employment income of JPY 6,190,000
Less social insurance premium deduction	JPY 1,050,000, fully deductible
Less basic deduction	JPY 480,000
Taxable income	JPY 4,660,000
National income tax: 20% of taxable income less the JPY 427,500 fixed subtraction	JPY 504,500
Special reconstruction surtax at 2.1% of the national tax	JPY 10,594, giving JPY 515,094
Local inhabitant tax at approximately 10% plus the per-capita levy	Roughly JPY 476,000, billed from June on the prior year's income

Final Deducted Result:Annual net take-home of approximately JPY 3,959,000, about JPY 330,000 a month, after social insurance of JPY 1,050,000, national tax and surtax of JPY 515,094, and inhabitant tax of roughly JPY 476,000. Total deductions run close to 29% of gross, of which social insurance alone is more than half. In your first year in Japan there is no inhabitant tax at all, so take-home is temporarily higher before the bill starts in the following June.

Frequently Asked Questions (FAQ)

What does shakai hoken actually cover?▼

Four things bundled into one payroll line: kenko hoken for medical treatment, which caps your share of most treatment costs at 30% and provides a high-cost medical expense benefit and sickness allowance; kosei nenkin, the earnings-related employees' pension that sits on top of the flat-rate basic pension; koyo hoken for unemployment, parental leave, and training benefits; and kaigo hoken for long-term nursing care, which is added from the month you turn 40 and charged until 64.

Why did my premiums rise when my salary did not?▼

Because of the teiji kettei annual review. Your standard monthly remuneration grade is set each year from the average of your April, May, and June pay, and it fixes premiums from September for the next twelve months. Heavy overtime or a one-off allowance in that three-month window pushes you into a higher grade for the whole following year even if your ordinary pay never changes. Grades only move mid-year through zuiji kaitei, which requires a substantial change in fixed remuneration sustained for three months.

What is nenmatsu chosei and do I still need to file a return?▼

Nenmatsu chosei is the December year-end adjustment in which your employer reconciles the tax withheld across the year against your actual liability, taking account of dependants and the deductions you declare on the year-end forms. It usually produces a refund in your December pay. You must still file your own kakutei shinkoku if salary exceeds JPY 20 million, if you have two or more employers, if side income exceeds JPY 200,000, or to claim the medical expense deduction, the first year of the housing loan credit, or a donation deduction.

Can I claim a refund of my pension contributions if I leave Japan?▼

Yes, within limits. A former participant who has contributed for at least six months and no longer has an address in Japan may claim the dattai ichijikin lump-sum withdrawal payment, generally within two years of leaving, with the amount based on contribution months up to a maximum number of months. Income tax is withheld at 20.42% on the pension portion, and appointing a tax representative before departure allows you to reclaim much of that withholding afterwards. A totalisation agreement may make it better to preserve the record instead.