The Korean Filing Calendar: One Deadline Vanished, and One Lands in 2027

What does a Korean subsidiary actually have to file, and when?

Ten separate recurring obligations, spread across three authorities and two portals. Two of them fall on the 10th of every month, four are quarterly, and the rest cluster into a nine-week run between the start of February and the end of April that quietly decides how the first quarter goes.

The calendar below is for the ordinary case: a Korean subsidiary of a foreign parent, December year end, employees on the payroll, VAT-registered, below the external audit threshold. Everything in it is dated to the authority it comes from.

Two entries have changed recently and most English-language guides have not caught up. One annual filing was abolished at the start of 2025 and is still being listed as live. Another becomes monthly on 1 January 2027, which is close enough that it belongs in next year’s budget rather than next year’s surprise.

The monthly filings

Two, both due on the 10th, both for the previous month.

The first is the withholding tax return. An employer pays salaries, withholds income tax under the simplified withholding table, and files and pays by the 10th of the following month. August payroll, 10 September. The National Tax Service is explicit that the return is due no later than the tenth day of the month following the month in which the salaries were paid. Local income tax withheld alongside it — a further 10% of the national withholding — goes to the local authority on the same date.

The second is the four major insurance premiums. Pension, health, employment and industrial accident are billed monthly and due by the 10th of the following month, the health insurance deadline being written into Article 78 of the National Health Insurance Act. Where the 10th falls on a weekend or public holiday, both roll to the next business day. What each of the four costs an employer is set out in our note on what Korea’s four major insurances cost in 2026.

There is a way out of the monthly withholding return, and it is under-used. An employer whose average headcount in the prior year was 20 or fewer may apply for approval to pay withheld tax half-yearly instead: January to June by 10 July, July to December by 10 January. Financial and insurance businesses are excluded. Applications go in twice a year, in June and December.

The quarterly filing

VAT, on four fixed dates, and there is no version of this that is optional for a corporation.

Korea splits the VAT year into two taxable periods, January to June and July to December, and then requires a preliminary return at the end of each of those periods’ first quarters. The practical effect for a company is four returns a year, each due 25 days after the quarter it covers.

Payment is due on the same date as the return, not later. Individual businesses get a lighter cycle; a corporation does not. The mechanics of the return, and the electronic tax invoice failures that destroy input VAT recovery, are covered separately in Korean VAT for a foreign-owned company.

The February-to-April run

This is the part that catches out a head office used to a single annual filing season.

February — year-end settlement. Korean employees do not file their own return on employment income. The employer reconciles the prior year’s withheld tax against the actual liability, collects deduction evidence from each employee, and settles the difference through the February payroll. An employee who over-withheld gets a refund in their February pay; one who under-withheld has the balance deducted.

End of February — payment statements for investment income. Statements for interest, dividend, pension and other income paid in the prior year are due by the last day of February.

10 March — payment statements for wage, retirement and business income. The annual statement, distinct from the simplified half-yearly one, covering every employee and every freelancer paid business income.

15 March — employment and industrial accident remuneration report. Filed with the Korea Workers’ Compensation and Welfare Service through its Total Service portal, declaring what each employee was actually paid in the prior year. It reconciles the premiums provisionally billed during that year and sets the monthly premium for the year ahead. Construction and forestry sit outside this and file on their own basis. Missing it, or filing it wrong, carries a fine of up to 3 million won and disqualifies the employer from the Duruimi social insurance subsidy.

31 March — corporate income tax return. Due within three months of the last day of the month in which the business year ends. The interim payment for the current year then falls on 31 August, which we covered when the interim payment rate went up.

30 April — local corporate income tax return. A separate return, to the local authority rather than the tax office, due within four months of year end under Article 103-23 of the Local Tax Act. It is filed on Wetax, not Hometax. That is the whole reason it gets missed: a company that has just filed its national return on 31 March and closed the file has one more return outstanding and no prompt from the system it just used.

The filing that no longer exists

Until 2024, an employer also filed an annual remuneration report with the National Health Insurance Service by 10 March. It was abolished with effect from 1 January 2025.

The amended Enforcement Decree of the National Health Insurance Act treats an employer who has filed the simplified payment statement for wage income with the National Tax Service as having given the health insurance service the same information. One filing now does the work of two.

What has not changed is the settlement. Health insurance premiums are still reconciled in April against actual prior-year remuneration, and an employer can still face a material additional payment or refund in the April billing. Only the separate filing went; the money did not.

This matters commercially in a way that is worth being blunt about. A foreign-owned company whose Korean compliance is handled by a provider working from a checklist written before 2025 may still be billed for preparing a filing that the authority no longer accepts. It is worth asking.

The filing that arrives in 2027

The simplified payment statement for wage income is currently half-yearly. January to June is due by 31 July; July to December by 31 January of the following year. That is the position for the whole of 2026.

From 1 January 2027 it becomes monthly, due by the last day of the month following payment. Employers with 20 or fewer employees in the prior year who are approved for semi-annual withholding payment have the monthly requirement deferred until 31 December 2028.

Two consequences follow, and neither is administrative trivia.

The first is that the filing now feeds health insurance. Since the 2025 change, the remuneration figures the health insurance service reconciles against come from this statement. A statement filed late, or filed with the wrong remuneration base, moves two authorities’ numbers, and the second error surfaces in the April billing rather than at the tax office.

The second is a resourcing question. Monthly submission turns one reconciliation task into twelve, and it lands on the same 10th-of-the-month payroll close that is already the busiest point in a Korean finance calendar. For a subsidiary running payroll with one part-time bookkeeper, 2027 is the year that stops working. That is the conversation to have in the 2027 budget, not in February 2027 — and it is the practical case for payroll outsourcing at the point where an in-house arrangement stops scaling.

What this looks like in one table

Two entries a reader may be looking for and will not find here. The health insurance remuneration report is gone. And the external audit obligation, which brings its own filing calendar, only starts once a company crosses the two-of-four audit test — below that threshold it does not apply at all.

An honest note on where this ends and an engagement begins. The calendar above is the standard case, and most foreign-owned subsidiaries are the standard case. A company with a non-December year end, a Korean branch rather than a subsidiary, employees seconded from the parent, or a permanent establishment question shifts several of these dates and adds others. If your entity is one of those, the calendar is a starting point, not an answer — and our tax and VAT compliance team can map the real one against your facts.

Figures current as at 30 August 2026. Korean filing deadlines and thresholds are revised regularly, and the simplified payment statement frequency changes on 1 January 2027 — each figure above is linked to the authority it was read from.