Method & sources

Every rate used by the calculators, the official page it came from, and when we checked it. Last full check: 6 October 2026.

Official pages are in Japanese. Where a rule changes during the year (as the 2026 tax deductions did, from 1 December 2026), we say how we treat it.

1. Take-home pay

Formula

1. Standard monthly remuneration: look up monthly pay in the 50-grade health table and the 32-grade pension table.
2. Health line = standard × (prefecture rate + 1.62% if age 40–64 + 0.23%) ÷ 2. Pension = standard × 18.3% ÷ 2. Each rounded the way payroll does: 50 sen or less dropped, over 50 sen rounded up.
3. Employment insurance = actual pay × 5/1,000 (same rounding).
4. Bonuses: standard bonus = bonus rounded down to ¥1,000; the same rates apply, with a ¥1.5M cap per payment for pension and a ¥5.73M yearly cap for health.
5. Income tax: employment income (2026 table) − social insurance − basic deduction − spouse − dependents = taxable income, rounded down to ¥1,000 → rate table → × 102.1%, rounded down to ¥100 (as in the year-end adjustment).
6. Resident tax (estimate on the same income): employment income − social insurance − ¥430,000 − ¥330,000 per spouse/dependent → rounded down to ¥1,000 → 6% municipal and 4% prefectural, minus the adjustment credit (3% and 2% of the smaller of the deduction gap and taxable income; above ¥2M taxable: of the gap minus the excess over ¥2M, at least ¥50,000) → each rounded down to ¥100 → + ¥5,000. Large-city non-taxable thresholds: total income ≤ ¥350,000 × (people) + ¥100,000 (+ ¥320,000 for the income levy / ¥210,000 for the per-capita levy if you have dependents).
7. First year in Japan: resident tax is charged only if you were registered in Japan on 1 January, so it is set to ¥0 for this year. The estimate shows what to expect from June of the following year.

How we treat the 2026 mid-year change

The higher basic deduction and employment income deduction for 2026 income took effect on 1 December 2026 and apply to the whole 2026 year. Payroll withholding from January to November 2026 is based on the earlier rules; the employer settles the difference at the year-end adjustment in December. The calculator shows the final 2026 income tax after that adjustment, so the "per month" figure is an average, not what each payslip shows.

The Kyokai Kenpo FY2026 rates (from March 2026) and the support levy (from April 2026) are applied to all 12 months for simplicity.

2. Pension lump-sum withdrawal

Formula

1. Months used = coverage months rounded down to a multiple of 6, maximum 60 (last coverage month April 2021 or later). Under 6 months: not eligible.
2. Employees' Pension: payment rate = 18.3% × ½ × months used, rounded to one decimal place. Amount = average standard remuneration × payment rate.
3. National Pension: amount = monthly premium in the fiscal year of the last payment × ½ × months used.
4. Withholding (Employees' Pension only) = amount × 20.42%, rounded down to ¥1.
5. Refund estimate (rough): retirement income deduction = max(¥800,000, ¥400,000 × years), years = coverage months ÷ 12 rounded up; taxable = (amount − deduction) ÷ 2 (for 5 years or less, only the first ¥3M is halved); tax = rate table × 102.1%; refund = withholding − tax. Assumption, not confirmed in an official source: "years of service" equals the coverage period.

3. Move-in cost

Formula: deposit = rent × months; key money = rent × months; agency fee = rent × months × 1.1; guarantor = (rent + fee) × %; prorated rent = (rent + fee) × remaining days ÷ days in month (rounded down); plus insurance, key change, optional next month's rent and other fees.

Testing

The calculation code is tested against official worked examples where they exist (NTA rate-table example, the NTA 2026 year-end adjustment example, the NTA 2026 employment-income table, the Kyokai Kenpo FY2026 Tokyo premium table, the Japan Pension Service lump-sum tables and the NTA sample refund return). Cases without an official example are marked as hand-calculated.

Corrections

Found a mistake? Use the contact form. Corrections will be listed here with the date.