Before you start

A residency basis to assess — a domicile/settled life in Korea or 183+ days of presence in the tax year.
An Alien Registration Card (ARC); its 13-digit registration number doubles as your individual tax ID.
Knowledge of your income types — Korean employment, foreign-source income, freelance (사업소득), other.
Hometax access (hometax.go.kr) — or your employer's payroll/HR for year-end settlement.

Step-by-step

1
Work out your residency and what is taxable
You are a resident if you have a domicile in Korea or a residence here for 183+ days in a tax year. Residents are taxed on worldwide income; non-residents only on Korea-source income. Crucially, if you have been resident 5 years or fewer of the last 10, your foreign-source income is taxed only when paid by a Korean payer or remitted into Korea — so newer arrivals can often keep overseas income out of the Korean net.
OnlineWho: You (with a tax accountant if you have foreign income)Assess once on arrival, re-check yearly
2
Employees: payroll withholding + year-end settlement (연말정산)
Employers withhold income tax (plus 10% local surtax) from each monthly salary. After the calendar year ends, the employer runs the year-end settlement in January-February using NTS's pre-filled Simplified Year-End service, applying your deductions and credits, and files the final receipt by 10 March. Any over- or under-withholding is squared up — refunds (the so-called '13th-month pay') usually land in the February/March payslip. If you have ONLY Class A salary, you normally do not file a separate return.
Via employerWho: Employer payroll / HR, with documents from youJan-Feb (employer files by 10 Mar)
3
Consider electing the 19% flat tax for foreign workers
Foreign employees may elect a flat 19% on total Korean employment income (about 20.9% with the local surtax) instead of the 6%-45% progressive scale, for up to ~20 years from your first day of work. It forfeits every deduction, exemption, and credit, and excludes people with a controlling stake in their employer. It usually wins above roughly KRW 130-150 million (about US$95,000-110,000) of salary. Elect it via the year-end settlement, your monthly withholding, or the annual return.
Via employerWho: You — choose with your employer or tax accountantElect annually; valid up to ~20 years
4
Freelancers / contractors: 3.3% withholding + business registration
Korean clients withhold 3.3% from freelance pay (3% income + 0.3% local) as a prepayment of tax on business income (사업소득). This is only a credit against your real liability, not a final tax. If self-employment is sustained, register as a sole proprietor (사업자등록) with the NTS within 20 days of starting — note that once registered you generally fall out of 3.3% withholding and instead charge and remit 10% VAT.
OnlineWho: You (sole proprietor) via HometaxRegister within 20 days of starting
5
File the May global income tax return (종합소득세) on Hometax if needed
Freelancers, the self-employed, anyone who elected the flat tax, and employees with extra reportable income must file a global income tax return covering the prior calendar year between 1 May and 31 May via Hometax (hometax.go.kr), paying any balance by 31 May. The NTS offers English-language guidance and an English help line (call 126) for foreign taxpayers. Filing itself is free.
OnlineWho: You — or a tax accountant (세무사) for business income1-31 May each year

Documents you’ll need

Alien Registration Card (ARC) — the registration number is your tax ID.
Employment/withholding receipts and the year-end settlement (연말정산) statement from your employer.
Deduction evidence — National Pension/health contributions, housing, medical, education, donations, dependents.
For freelancers: business registration (사업자등록증) if registered, plus 3.3% withholding receipts and income/expense records.

Things most newcomers don’t know

The flat 19% election (~20.9% with the local surtax) can slash tax for higher earners — but it strips out every deduction and credit, so it only wins above roughly KRW 130-150 million salary.

The progressive top marginal rate is 45% (49.5% with surtax), so a flat ~20.9% is dramatically lower at high incomes; below the break-even, keeping deductions under the progressive scale is better. Many expats default to progressive and overpay.

Source: PwC Tax Summaries — Korea, Taxes on personal income (2026)

If you have been a Korean resident for 5 years or fewer of the last 10, your foreign-source income is taxed only when a Korean entity pays it or you remit it into Korea.

This 'short-term resident' rule means new arrivals can usually keep overseas salary, investments, and rental income outside Korean tax — a major, often-missed relief that ends once you cross the 5-year mark and become taxable on worldwide income.

Source: PwC Tax Summaries — Korea, Income determination (2026)

Most salaried employees never file a tax return at all — the employer's year-end settlement (연말정산) in January-February is how 'doing your taxes' works in Korea.

Employers reconcile your full-year liability using NTS pre-filled data and pay any refund through payroll, so a pure salary earner has no May filing. People wrongly assume they must file and miss the simpler reality (and the deduction-upload window in January).

Source: National Tax Service (NTS) Year-End Tax Settlement; PwC Tax administration

The 3.3% withheld from freelance pay is only a prepayment — you still settle the real bill in the May global income tax return (종합소득세).

Freelancers see 3.3% taken at source and assume tax is done; in fact it is credited against the progressive liability in May, and depending on income and expenses you may owe more or be refunded. Registered sole proprietors also pick up a 10% VAT obligation.

Source: NTS Hometax; PwC Tax Summaries — Korea (2026)

Common mistakes to avoid

Not electing the 19% flat tax when your salary is high enough to save under it — or, conversely, electing it and then losing valuable deductions you would have kept on the progressive scale.
Tripping the 183-day or domicile test unawares and becoming a worldwide-income resident — and forgetting that the foreign-income relief ends after 5 of the last 10 years.
Freelancers treating the 3.3% withholding as final tax and skipping the mandatory 1-31 May global income tax return (or missing the 20-day business-registration window).
US citizens forgetting they must still file with the IRS every year (using the Foreign Earned Income Exclusion or Foreign Tax Credit) even after paying Korean tax — the Korea-US treaty does not remove the US filing duty.