Japan Bonus Calculator (賞与計算機)
Convert a gross 賞与 (bonus) into net take-home. Applies the NTA bonus tax table, prefecture-specific health insurance, the welfare-pension per-payment cap, and the no-resident-tax rule that surprises most employees.
Bonus net-take-home calculator
How it works
How a Japanese bonus is taxed and what actually hits the bank
Japanese bonuses (賞与) are subject to social insurance and income tax just like monthly salary, but the exact mechanics differ in three important ways: the income tax rate uses a separate NTA table indexed by previous month's net salary, the social insurance contributions are capped per payment and per fiscal year, and resident tax is not deducted from bonuses at all. The result is that the net take-home percentage of a bonus is usually higher than the net take-home percentage of monthly pay for the same employee.
1. Standard bonus amount (標準賞与額)
For social insurance, the gross bonus is first floored to the nearest 1,000 yen. This is the standard bonus amount on which Kyokai Kenpo (or Kumiai-Kenpo) and welfare pension contributions are computed. A 487,650 yen bonus becomes 487,000 yen for SI purposes.
2. Health insurance and long-term care (健康保険・介護保険)
Health insurance is calculated at the same prefecture-specific Kyokai Kenpo rate that applies to monthly salary, with the employee paying half. Tokyo's FY2025 combined rate is 9.91%, so the employee deduction is 4.955%. Long-term care insurance (national rate 1.59% combined) applies only when the employee is between 40 and 64. At age 40 it begins automatically starting with the month they turn 40, and ends when they reach 65.
Both have a combined annual cap: across all bonuses paid in a single fiscal year (April through March), only the first 5.73 million yen cumulative is subject to health insurance and long-term care contributions. Anything beyond escapes both. The calculator tracks this via the cumulative bonus field.
3. Welfare pension (厚生年金)
Welfare pension is at 18.30% combined (locked at this rate since September 2017), with the employee paying half. The cap is different from health insurance: it applies per bonus payment, not per fiscal year. Only the first 1.5 million yen of any single bonus is subject to pension. A 4 million yen bonus is treated as if it were 1.5 million for pension calculation only.
4. Employment insurance (雇用保険)
Employment insurance applies to the full gross bonus with no cap. Employee rate is 0.55% for general business and 0.65% for construction, agriculture/forestry/fishing, and sake manufacturing (FY2025).
5. Income tax via the NTA bonus rate table
This is the part most employees don't expect. Income tax on a bonus is not computed at the employee's annual marginal rate; it is looked up from the 賞与に対する源泉徴収税額の算出率の表 (bonus withholding rate table), which returns a percentage based on:
- The previous month's salary after social insurance deduction (前月の社会保険料控除後の給与)
- The number of tax dependents on the source deduction declaration
The percentage already includes the 2.1% reconstruction surtax (which is why the rates show awkward decimals like 6.126% instead of 6%). The percentage is then applied to the bonus amount after social insurance has been deducted.
Two exception rules under Income Tax Law Article 186 trigger a different calculation: if the previous month had no salary, or if the bonus amount is more than ten times the previous month's net salary, an averaging method is used instead. This calculator implements the standard table; for the exception cases consult your payroll provider.
6. Resident tax (住民税): NOT deducted from bonus
Unlike income tax, resident tax in Japan is computed retrospectively on the previous calendar year's total income (including bonuses) and is billed in 12 equal monthly installments from June to May of the following year, deducted from monthly salary only. Bonuses are explicitly excluded from current-cycle resident tax withholding. This is the single biggest reason a bonus's net-take-home percentage looks better than a monthly salary's.
7. Putting it together
For a 30-year-old Tokyo employee receiving a 500,000 yen bonus with a 290,000 yen previous-month net salary and zero dependents, the deductions look approximately like this (rounded to the nearest yen):
- Health insurance: 500,000 × 4.955% = ~24,775
- Welfare pension: 500,000 × 9.15% = ~45,750
- Employment insurance: 500,000 × 0.55% = ~2,750
- Income tax: (500,000 − above) × 4.084% = ~17,427
- Resident tax: 0
- Net take-home: ~409,298
That's about 81.9% of gross, well above the typical 75-78% of monthly salary, almost entirely because of the absent resident tax line.
Reference
Key terms and concepts
Standard bonus amount (標準賞与額)
The gross bonus floored to the nearest 1,000 yen. This is the figure used for social insurance contribution calculations (per Health Insurance Act Art. 45 and Welfare Pension Insurance Act Art. 24).
Bonus tax rate table (賞与に対する源泉徴収税額の算出率の表)
The NTA-published table that returns the bonus income tax rate based on previous month's net salary and number of dependents. Current version applicable since 令和2年, with rates including the 2.1% reconstruction surtax.
Cumulative annual bonus cap (健保 573万円)
Across all bonuses paid in a single fiscal year (April-March), only the first 5.73 million yen cumulative is subject to health insurance and long-term care insurance contributions. Set by ministerial ordinance.
Per-payment pension cap (厚年 150万円)
For welfare pension, only the first 1.5 million yen of any single bonus is subject to contribution. Unlike health insurance, this cap does not aggregate across bonuses.
Long-term care insurance trigger (介護保険・40〜64歳)
Long-term care insurance applies from the month the employee turns 40 until the month they turn 65. Combined Kyokai-Kenpo rate is 1.59% nationally for FY2025; the employee pays half.
Kyokai Kenpo vs Kumiai-Kenpo (協会けんぽ vs 組合健保)
Kyokai Kenpo is the default health insurance scheme operated by the Japan Health Insurance Association, with prefecture-specific rates around 9-10%. Kumiai-Kenpo are company or industry-specific health insurance unions with their own rates, typically 1-2 percentage points lower. Calculator supports both.
Resident tax (住民税)
Local tax computed on the previous calendar year's total income (including bonuses) and billed in 12 monthly installments from June through May of the following year. Always 10% of taxable income (split 6% prefecture / 4% municipality), with a small per-capita component. Not withheld from current-cycle bonuses.
Frequently asked
Common questions about Japan bonus pay
Why does the previous month's salary affect my bonus tax?
The NTA bonus rate table indexes the percentage rate by the previous month's net salary, as a quick proxy for the employee's marginal tax bracket. This avoids requiring the employer to recompute the full annual income tax mid-year for each bonus.
Is the bonus pay date or accrual date what counts for SI caps?
The payment date. The 5.73 million yen annual cap applies to bonuses paid (not accrued) within April-March. If a bonus is decided in March but paid on April 5, it counts toward the new fiscal year's cap.
What if the bonus is paid in two installments?
Each installment is treated as a separate bonus payment. The 1.5 million yen pension cap applies per installment, so splitting a 3 million yen bonus into two 1.5 million yen installments doubles the pension subject amount compared to a single 3 million yen payment.
Do part-time / baito employees get bonuses?
There is no statutory bonus right; bonuses are discretionary and governed by the work rules or employment contract. When part-time employees do receive bonuses, the same SI and tax rules above apply, including the SI thresholds for whether the employee is enrolled at all.
How are sign-on bonuses (入社時一時金) treated?
If paid as a 賞与 (subject to wage rules and reflected on a 賞与支払届), the same SI and tax rules apply. If structured as a 一時金 outside wage rules, it may be treated as ordinary salary or as 退職金-equivalent depending on the structure. Check with a sharoshi for non-standard arrangements.
What is the deadline to file the bonus payment notification?
Form 賞与支払届 must be filed with the pension office within 5 days of the payment date. Late filing can trigger administrative guidance and complicates SI premium calculation for both employer and employee.
Can the bonus tax rate ever exceed the marginal income tax rate?
In rare cases yes, particularly for employees with very low previous-month salary but a large bonus. In practice, the year-end adjustment (年末調整) reconciles to the actual annual marginal rate, so any over-withholding is refunded in December.
How do shacho (executive) bonuses differ?
Executive bonuses (役員賞与) are not deductible as a corporate expense unless filed in advance with the tax office (事前確定届出給与). The employee-side income tax and SI treatment is identical to ordinary employee bonuses.
Important. This calculator implements the FY2025 Kyokai Kenpo rates, the locked welfare pension rate, and the current NTA bonus withholding rate table. It is provided for general information only and does not constitute legal or tax advice. Special calculation rules under Income Tax Law Article 186, Kumiai-Kenpo unions with non-standard rates, and edge cases (mid-year prefecture changes, age-40 bonus crossings, executive bonuses) may produce different results. Verify against your payroll provider's output, and consult a licensed sharoshi (社会保険労務士) or tax accountant for binding answers.