If the income tax on your May return or November interim bill is large, you don’t have to pay it all at once. Income Tax Act Article 77 lets a resident whose tax due exceeds ₩10 million pay part of it within 2 months after the payment deadline, and Decree Article 140 sets how much: up to ₩20 million, the part over ₩10 million; over ₩20 million, up to 50/100 of the tax. Capital gains tax has the same rule in Article 112 and Decree Article 175. Enter the tax and the deadline to see what is due now, what may wait and the installment deadline.
1. Tax due over ₩10 million: part may be paid within 2 months (Income Tax Act Art. 77).
2. Up to ₩20 million, the part over ₩10 million; over ₩20 million, up to 50% of the tax (Decree Art. 140).
3. Same rule for the final return, sincere filing, the interim prepayment and capital gains (Arts. 77 and 112).
Calculator
Updates as you type. The 2 months are counted from the day after the payment deadline under the Civil Act method (Framework Act Art. 4); weekend deadlines move to the next day (Art. 5). Public holidays also move a deadline but are not applied here. Above ₩20 million we show 50% rounded down to the won (our method).
The installment articles
| Type | What the source says | Worth noting (ours) |
|---|---|---|
| Income Tax Act Art. 77 | A resident whose tax due under Art. 65 (interim prepayment), Art. 69 (land dealer estimate) or Art. 76 (final return) each exceeds ₩10 million may pay part of it within 2 months after the payment deadline | “Each”: each payment is looked at separately (our reading) |
| Decree Art. 140 | The amount that may wait: 1. tax ₩20 million or less: the part over ₩10 million; 2. tax over ₩20 million: up to 50/100 of the tax | — |
| Art. 112 · Decree Art. 175 | Capital gains tax due on a preliminary (Art. 106) or final (Art. 111) return over ₩10 million: same 2-month installment, same amounts | — |
| Arts. 70 and 70-2 | Final return from 1 May to 31 May; with a sincere-filing confirmation, to 30 June | — |
| Art. 65 | Interim prepayment collected by 30 November; the bill is issued 1–15 November | — |
How much may wait — our examples
| Tax due (our example) | Pay by the deadline / may wait | Worth noting (ours) |
|---|---|---|
| ₩9 million | ₩9 million / ₩0 | ₩10 million or less: no installment |
| ₩15 million | ₩10 million / ₩5 million | Up to ₩20 million: the part over ₩10 million |
| ₩20 million | ₩10 million / ₩10 million | At the boundary both rules give the same |
| ₩25 million | ₩12.5 million / ₩12.5 million | Over ₩20 million: up to 50% |
The amount that may wait is a ceiling; you may defer less. Above ₩20 million the calculator rounds the 50% down to the won (our method).
When is the installment due — our sums
“Within 2 months after the payment deadline” is counted the Civil Act way (Framework Act on National Taxes Art. 4): two months from the day after the deadline, moving to the next day if the last day is a weekend or holiday (Art. 5). The Civil Act method is in the legal period calculator.
| Payment (our example) | Deadline → installment deadline | Worth noting (ours) |
|---|---|---|
| 2026 final return | 1 June → 3 August | 31 May was a Sunday, so 1 June; 1 August is a Saturday, so 3 August |
| 2026 sincere filing | 30 June → 31 August | — |
| 2026 interim prepayment | 30 November → 1 February 2027 | 31 January is a Sunday |
| 2027 final return | 31 May → 2 August | 31 July is a Saturday |
The interim bill itself, and estimating it when business drops, is in the interim prepayment calculator. For the capital gains preliminary deadline (2 months from the end of the month of sale) see capital gains preliminary return, then enter it as “other deadline”.
Checklist
- ☐ Is the tax over ₩10 million (each payment separately)?
- ☐ Up to ₩20 million: the part over ₩10 million; above: up to half
- ☐ Installment due 2 months from the day after the deadline
- ☐ Last day on a public holiday: one more day
Questions that remain
Do I need to apply?
Art. 77 says installments follow the Decree, and Decree Art. 140 only sets amounts. We didn’t read the forms; follow the tax office’s guidance when you file.
What if I miss the installment deadline?
A late-payment penalty can apply; rates are in the tax penalty calculator.
Can local income tax be split too?
Local income tax is governed by the Local Tax Act, which we didn’t read this time.
Sources
- Korean law database (law.go.kr) — Income Tax Act Arts. 65, 70, 70-2, 76, 77 and 112 — source (current text, effective 1 July 2026, Act No. 21221; checked 27 October 2026). Installments (over ₩10 million, within 2 months after the deadline), capital gains installments, 31 May final return and 30 June sincere filing, 30 November interim prepayment.
- Korean law database — Income Tax Act Enforcement Decree Arts. 140 and 175 — source (effective 1 October 2026, Decree No. 36737; checked 27 October 2026). Amounts up to and over ₩20 million.
- Korean law database — Framework Act on National Taxes Arts. 4 and 5 — source (effective 2 October 2026, Act No. 21987; checked 27 October 2026). Civil Act counting and the deadline extension rule.
- Not read. The installment forms (Enforcement Rule), local income tax under the Local Tax Act, the Civil Act period articles (not re-read).
- What we added. The “worth noting” column and the Korean everyday gloss.
Where to check further
- Your tax office — how to apply, and when the last day meets a holiday.
Written on 27 October 2026. The content is from the source; the glosses are ours.
