Before you start

A view on your residence position — settled life in Korea, or 183 days in the tax year
An Alien Registration Card; its thirteen-digit number doubles as your tax identifier
Clarity on your income types: Korean employment, foreign-source, freelance business income
Hometax access, or your employer's payroll team

Step-by-step

1
Establish whether you are a resident and for how long you have been one
Residence turns on domicile or 183 days of presence. Then count how many of the last ten years you have been a Korean resident: at five or fewer, foreign-source income is taxed only if a Korean entity pays it or you bring it into Korea. Crossing that line moves you to worldwide taxation and nobody announces it.
OnlineWho: You, with a tax accountant if you hold foreign income or assetsAssess on arrival, re-check every year
2
Let the year-end settlement handle it if you are a straightforward employee
Employers withhold monthly and then run the year-end settlement in January and February using the tax office's pre-filled data, filing the final receipt by 10 March. Any over-withholding comes back through the February or March payslip. Employees with only Class A salary normally have no separate return to file.
Via employerWho: Your employer's payroll team, with documents from youJanuary–February
3
Run the numbers on the flat-rate election
Foreign employees may elect a flat 19% on Korean employment income, roughly 20.9% including the local surtax, for a long fixed window from your first day of work in Korea. It removes every deduction, exemption and credit, and excludes people with a controlling interest in the employer, so it wins only at high salaries. Compare both ways each year rather than deciding once.
Via employerWho: You, with your employer or a tax accountantElected annually
4
Freelancers: understand that the 3.3% is a prepayment
Korean clients withhold 3.3% from freelance fees. This is a credit against your real liability, not a final tax. Sustained self-employment means registering as a sole proprietor with the tax office shortly after you start, after which you generally charge and remit VAT instead of having 3.3% withheld.
OnlineWho: You, via HometaxRegister soon after starting
5
File the May global income return if you have anything beyond a single salary
Freelancers, the self-employed, people with multiple employers and anyone with extra reportable income file between 1 and 31 May for the previous calendar year and pay by the end of the month. Filing on Hometax is free; the tax office runs an English helpline on 126 for foreign taxpayers.
OnlineWho: You, or a licensed tax accountant1–31 May
6
Deal with the tax side of leaving before you leave
Departure part-way through a year means a settlement of employment income, and freelancers may have a return still due. Closing bank accounts and reclaiming pension from abroad is much harder than doing it here. Give yourself a working month before the flight for the tax, pension and account items together.
OnlineWho: YouBefore departure

Documents you’ll need

Alien Registration Card — the registration number is your tax identifier
Withholding receipts and the year-end settlement statement from your employer
Deduction evidence: pension and health contributions, housing, medical, education, dependants
Business registration certificate, 3.3% withholding receipts and expense records, for freelancers
Records of foreign income and remittances into Korea

Things most newcomers don’t know

The five-year window on foreign income is the most valuable relief most newcomers never hear about.

Resident for five years or fewer of the last ten, your overseas salary, investments and rental income fall outside Korean tax unless a Korean entity pays them or you remit them here. That is a large planning space for anyone with assets abroad, and it closes silently once you cross the threshold. Knowing the date it closes is worth an appointment with an accountant in year four.

Source: PwC Worldwide Tax Summaries — Korea, residence and income determination

The flat 19% election is a trap below its break-even and a large saving above it.

It replaces the progressive scale with a single rate on Korean employment income but strips out every deduction and credit at the same time. The break-even sits well into the six figures in US dollar terms, so mid-range earners who elect it because it sounds simple end up paying more. Model both each year — the election is annual, not permanent.

Source: PwC Worldwide Tax Summaries — Korea, taxes on personal income

Korea's local surtax follows where you live, but it is not a Busan rate you can shop for.

The 10% local income tax is calculated as a fixed proportion of your national income tax and paid to the municipality where you reside. So living in Busan rather than Seoul does not change your income tax bill at all — unlike property acquisition and holding taxes, which do vary. People move south expecting a tax saving and find it in rent and living costs instead.

Source: National Tax Service

The 3.3% deducted from freelance invoices is not your tax bill.

Korean clients withhold 3.3% from business income as a prepayment, and it is credited against a progressive liability settled in the May return. Freelancers who treat it as final tax discover in year two that they owe a substantial balance, or conversely that they have been overpaying and never claimed the refund. Either way the May filing is not optional.

Source: National Tax Service — Hometax

Common mistakes to avoid

Not tracking when the five-year foreign-income window closes and becoming taxable on worldwide income unawares.
Electing the flat rate at a salary below its break-even and losing deductions worth more.
Assuming moving from Seoul to Busan reduces your income tax — it does not.
Freelancers treating the 3.3% withholding as a final tax and skipping the May return.
US citizens forgetting that the treaty does not remove their annual IRS filing obligation.

Some of this may be out of date. Spotted something inaccurate? Help us keep it right for the next newcomer.