How is tax on a Korean bonus calculated?

By the payment-period method: tax on (monthly salary + bonus ÷ months) minus tax on the monthly salary, multiplied by the number of months. This spreads the bonus so it is not all taxed in the top bracket at once.

Why is my one-off bonus taxed so heavily?

With a 1-month payment period, the whole bonus is added to one month's pay, pushing it into a higher bracket. The over-withheld amount is typically refunded at year-end tax settlement (연말정산).

Does this tool upload my data?

No. Everything runs right in your browser, so your data never leaves your device — it even works offline once the page has loaded.

🎁 Korean Bonus / Performance Pay Tax Calculator

Enter your bonus amount, monthly taxable salary, and the bonus payment period to estimate the withholding income tax and your net bonus. Korea taxes bonuses with a payment-period method, so this tool spreads the bonus over its period before applying the simplified withholding table. Runs entirely in your browser — free and offline.

Inputs

Bonus amount (상여금·성과급, KRW)

Monthly taxable salary (월 과세급여, KRW)

Payment period, months (지급대상기간)

Dependents incl. self (부양가족 수)

Children aged 8–20 (8~20세 자녀 수)

Bonus withholding uses the payment-period method: tax on (salary + bonus÷months) minus tax on salary, × months. Set months = the bonus's payment period (1 for one-off performance pay). Income tax only — insurance may apply separately. Estimate.

Bonus income tax (상여 소득세)

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Local income tax (지방소득세)

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Net bonus (실수령)

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Private by design. This tool runs entirely in your browser — nothing you enter is uploaded or stored, and it works offline.

About

Bonus withholding tax is estimated with the payment-period method: (1) tax on (monthly salary + bonus ÷ payment months), (2) minus tax on the monthly salary alone, (3) × payment months. Both tax figures use the 2026 NTS simplified withholding table (간이세액표) with dependent and child adjustments. Local income tax is 10% of the income tax. For a one-off performance bonus, set the payment period to 1 month; for a regular bonus, use its covered period. This estimate covers income tax only — national pension, health and employment insurance may also apply and are settled against annual pay. Final tax is trued up at year-end (연말정산). All calculations run client-side.

How to use

Enter the bonus amount (상여금·성과급) and your monthly taxable salary (월 과세급여).
Set the payment period in months (지급대상기간) — 1 for a one-off performance bonus.
Enter dependents and children aged 8–20 for tax adjustments.
Read the bonus income tax, local income tax, and your net bonus after tax.

FAQ

How is tax on a Korean bonus calculated?: By the payment-period method: tax on (monthly salary + bonus ÷ months) minus tax on the monthly salary, multiplied by the number of months. This spreads the bonus so it is not all taxed in the top bracket at once.
Why is my one-off bonus taxed so heavily?: With a 1-month payment period, the whole bonus is added to one month's pay, pushing it into a higher bracket. The over-withheld amount is typically refunded at year-end tax settlement (연말정산).
Does this include insurance deductions?: No — this estimates income tax and local income tax only. National pension, health and employment insurance may also be levied on a bonus and are reconciled against your annual pay.
Does this tool upload my data?: No. Everything runs right in your browser, so your data never leaves your device — it even works offline once the page has loaded.