The one-line formula
Tax already withheld − final income tax = refund (+) or amount due (−). Local income tax of 10% moves in the same direction. Korean employees call a big refund the “13th-month salary” and a bill a “tax bomb”, but the mechanism is the same.
Six common reasons
| Reason | What went wrong | Where to check |
|---|---|---|
| You chose 80% withholding | Too little withheld | Payslip income tax line, HR |
| A raise or bonus mid-year | Too little withheld + higher bracket | Monthly payslips |
| You changed jobs and income wasn’t combined | Each employer withheld at a low rate | Previous employer’s withholding receipt |
| A couple both claimed the same dependent | Over-deduction, corrected later with penalty | Dependent list |
| Your residency status differs from what was assumed | Non-residents can’t claim dependents or special deductions | HR, NTS |
| Card spending under 25% of gross pay | Card deduction is zero | Hometax preview |
Residency matters for foreign employees: according to the NTS, foreign workers who are tax residents can claim most deductions like Korean nationals (the housing-savings deduction is an exception), while non-residents cannot claim dependents, special income deductions or the child tax credit.
What to check before November
- Did your monthly income tax drop compared with last year? That usually means a lower withholding rate or a change in declared dependents.
- Did you change employers, take leave or get a bonus? All earned income for the year must be combined.
- Hometax year-end settlement preview — the NTS opened the preview for the 2025 tax year on 5 November 2025, using January–September card data. Watch Hometax for this year’s opening.
Finding the cause with the app
The Android app Year-End Tax Calculator estimates the result with the 2025 tax-year formula and the major deductions. Use it to change one thing at a time and watch the result move.
Enter salary and spending
On the Calculator tab, enter annual gross salary (taxable part), dependents, card spending, housing savings and medical expenses, all in units of 10,000 KRW.
Set withholding rate and tax already paid
Open “Advanced (optional)” to pick the withholding rate option (80/100/120%) and to enter tax already paid. If left blank, the app estimates tax already paid from salary and dependents, assuming no card, housing or medical deductions. For a realistic result, enter the income tax total from your payslips.
Read the step-by-step breakdown
Look for lines at zero (card deduction, housing-savings deduction) and compare “Tax already paid” with “Final tax (income)”.
The app’s English screens show amounts with the Korean won sign, and the saved-scenario card keeps a few Korean labels in the current version.
FAQ
When is the amount due taken?
Most employers settle it through February (sometimes March) pay. If it is large, ask HR whether it can be split. Timing depends on the employer.
Last year was a refund, this year a bill. Why?
A raise, a different withholding rate, a change in dependents or in card spending are the usual causes. See raises and tax brackets.
Sources: Korea.kr, 2025 year-end settlement preview opens (Korean) · Korea Tax Times, year-end settlement for foreign workers (Korean) · NTS Hometax
Year-End Tax Calculator
No sign-up, works offline, and your salary data stays on your phone. Free on Android, in English and Korean.