A bill arrives in November for tax you have not yet earned. You paid global income tax in May, and here is another demand. This is the interim payment — the state collecting about half of next May's tax in advance.
1. It is not "half of what you paid last May". The statute adds last November's interim payment too, then halves the sum (art. 65(7)).
2. Under 500,000 won nothing is collected at all. It is not a discount — the tax is simply not levied (art. 86(4)).
3. A weak first half lets you switch. Where the estimate falls below 30% of the basis, you file that figure instead (art. 65(3)).
4. Above 10m won you may pay in two parts — within two months (art. 77).
Enter the two amounts you paid last year and this year's first-half income, and it shows the notice and the estimate side by side.
It follows the order the statute sets. The basis is last year's interim tax plus the tax paid on the final return and similar amounts, less any refund (art. 65(7)), and the notice is half of it — amounts under 1,000 won are dropped (art. 65(1)). Where that figure is under 500,000 won it is not collected at all (art. 86(4)). If the first half went badly and the estimate falls below 30% of the basis, you may file that figure instead between 1 and 30 November (art. 65(3)), and filing voids the notice (art. 65(4)). The estimate is (first-half income x 2, less losses carried forward and deductions), taxed at the basic rates, then halved (art. 65(8)). Credits, reliefs, tax withheld at source, interim returns on land and building gains, and penalties are not included. People whose only income is interest, dividends, employment, pension or other income, and anyone who started a business this year, are outside the scheme (Decree art. 123). An estimate.
The basis adds up two payments, not one
This is where most explanations go wrong. "Half of the tax you paid last May" is the usual line, and the statute does not say that.
Article 65(7) The basis for the interim payment under paragraph (1) shall be the sum of the following amounts, less … any refund.
1. the interim tax for the preceding taxable period 2. the tax paid on the final return 3. additional tax payable, penalties included 4. tax paid on a late return or by voluntary further payment
Subparagraph 1 is what you paid last November. Count only May and the basis falls short by that amount — and the notice by half of it.
Pay 3m won last May and 2m won last November and the basis is 5m won, the notice 2.5m won. Counting May alone gives 1.5m won — 1m won out.
A refund reduces it. Article 65(7) deducts any refund under article 85 from the sum, and adds in brackets that where a claim for correction has been determined, the figure as corrected is used.
Leave the November field at zero if nothing was billed. That happens where last year's interim tax was under 500,000 won, or where last year was the first year of trading.
Under 500,000 won nothing is collected
Where the interim tax is small, no bill is issued at all. Article 86 calls this "non-collection of small amounts".
Article 86 (Non-collection of small amounts) In any of the following cases the income tax shall not be collected.
4. where the interim tax under article 65 is less than 500,000 won
The notice is half the basis, so a basis of 1m won is the line. Below it the figure is zero; at it, 500,000 won appears in a single step.
It is "less than", so a basis of exactly 1m won is billed in full. And before the comparison, amounts under 1,000 won are dropped (art. 65(1)) — 499,999 won becomes 499,000 won first, then meets the 500,000 test.
A weak first half lets you switch
If last year was good and this first half was not, a bill computed on last year's figures stings. The statute leaves open a route: recompute on actual results and file.
Article 65(3) … where the income tax on total income up to the end of the interim period (the estimate) falls below 30 per cent of the basis, the resident may file that amount … between 1 and 30 November.
The route is not open at will. There is a 30% threshold. And once you file, "the determination of the interim tax under paragraph (1) shall be deemed not to have been made" (art. 65(4)) — the notice disappears entirely.
How the estimate is computed
Article 65(8) sets it out in three lines. The third line is an image inside the article and does not come out as text — we read it from the alt attribute.
1. Tax base = (total income for the interim period x 2) − losses carried forward − deductions
2. Gross tax = tax base x the basic rates
3. The estimate = (gross tax ÷ 2) − (reliefs and credits, tax on an interim return of gains on land and buildings, occasional assessments and tax withheld at source)
The "basic rates" in line 2 are article 55. That table is an image inside the article too, and was read from the alt in the same way.
| Tax base | Gross tax |
|---|---|
| up to 14m won | 6% |
| 14m won – 50m won | 840,000 won + 15% of the excess |
| 50m won – 88m won | 6.24m won + 24% of the excess |
| 88m won – 150m won | 15.36m won + 35% of the excess |
| 150m won – 300m won | 37.06m won + 38% of the excess |
| 300m won – 500m won | 94.06m won + 40% of the excess |
| 500m won – 1bn won | 174.06m won + 42% of the excess |
| over 1bn won | 384.06m won + 45% of the excess |
| Income Tax Act art. 55(1). Middle ranges read "over the first figure, up to the second". The 384.06m won in the last row was missing from the alt; we carried it forward from the band above. | |
Double the half-year income to a full year, tax it, then halve the tax. Because the rates are progressive, that is not the same as taxing six months of income directly. It is why the statute doubles first and halves after.
On first-half income of 12m won with 5m won of deductions: a tax base of 19m won, gross tax of 1.59m won, an estimate of 795,000 won.
With a basis of 10m won the threshold is 3m won, and on 5m won of deductions the estimate only drops below it where first-half income is under 26.7m won.
Above 10m won you may pay in two parts
Article 77 opens deferral to the interim payment as well, not just the final return.
| Tax due | Amount that may be deferred |
|---|---|
| up to 10m won | none |
| 10m won – 20m won | the amount above 10m won |
| over 20m won | up to 50% of the tax |
| Art. 77 and Decree art. 140. The window is two months after the due date. | |
At 15m won you may defer 5m won; at 30m won, 15m won. It reads "exceeds", so exactly 10m won does not qualify.
Questions that remain
I am on a salary. Why does no bill reach me?
Because you are outside the scheme. The bracket in article 65(1) excludes "a person whose only income is income prescribed by Presidential Decree", and Decree article 123 names that as interest, dividends, employment, pension and other income. Separately taxed residential rental income and office-support service income are excluded too.
I started trading this year.
The same bracket excludes "a person who was not a business operator at the start of the taxable period and newly started a business during it". But double-entry bookkeepers are different: even with no basis, article 65(5) says they shall file the estimate. Not may — must.
What if I miss 30 November?
Article 65(2) is worth reading. Of the unpaid tax, the part that could have been deferred is deemed never to have been billed, and the office issues a fresh notice for it between 1 and 15 January of the following year. The rest is simply in arrears.
When does the bill arrive?
The second sentence of article 65(1) requires it to be issued between 1 and 15 November. The due date is 30 November. If you mean to file an estimate instead, note that the filing window is also 1 to 30 November — the two overlap.
What happens to the money?
It is credited against next May's final return as tax already paid. Pay too much and you get it back — this is money paid early, not money lost.
Sources
Income Tax Act [in force 1 January 2026] — art. 65 (interim payment), art. 55 (rates), art. 77 (payment in instalments), art. 86 (non-collection of small amounts).
Enforcement Decree of the same Act — art. 123 (income outside the scheme), art. 124 (the notice), art. 140 (the deferrable amount).
Both the formula in article 65(8)3 and the rate table in article 55 are published as images inside the articles. Neither is reachable as text, so both were read from the alt attribute. The last row of the rate table, though, was not complete even in the alt — it ended at "45 per cent of the amount exceeding 1bn won", with the 384.06m won before it missing. We carried the calculation forward from the band above to fill it in.
The script was checked against the same model across 2,142 combinations — 17 final-return figures x 6 interim figures x 7 first-half incomes x 3 deduction figures, all matching, with 500,000 won, 10m won, 20m won and the 30% threshold tested one won either side.
Where to check
The May return itself is covered in global income tax and the income tax calculator; if 3.3% was withheld from you, the freelancer refund follows. Side income is in side-job income tax, VAT in the VAT calculator, and the year's dates, 30 November included, are collected in the tax calendar.
