Before you start

A view on your residence position — settled life in Korea, or 183 days
An Alien Registration Card; its thirteen-digit number is your tax identifier
Clarity on income types: Korean employment, research stipend, foreign-source, freelance business income
Resident registration at your rented address, if you want the rent credit

Step-by-step

1
Establish residence and how long you have held it
Residence turns on domicile or 183 days of presence in the tax year. Then count how many of the last ten years you have been 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 threshold moves you to worldwide taxation and nothing announces it.
OnlineWho: You, with a tax accountant if you hold foreign income or assetsAssess on arrival, re-check annually
2
Check whether a tax treaty exempts your teaching or research income
Several of Korea's double-tax treaties contain a professors-and-researchers article exempting income from teaching or research at an approved institution for a limited period, commonly two years. Whether it applies depends on your nationality, the institution and the exact wording of that treaty — it is not automatic and it is not universal. In a city built on research appointments this is worth an hour with the institute's administration or a tax accountant before your first year-end settlement, not after.
Via employerWho: You with your institute and a tax accountantBefore your first settlement
3
Let the year-end settlement do it if you are a plain employee
Employers withhold monthly and run the year-end settlement in January and February against the tax office's pre-filled data, filing the final receipt by 10 March. Over-withholding comes back through the February or March payslip. Employees with only Class A salary normally file nothing separately.
Via employerWho: Your employer's payroll team, with documents from youJanuary–February
4
Claim the monthly rent tax credit at year-end settlement
Employees below an income threshold can claim a credit on rent paid, at a rate and up to an annual cap that are both revised most years. The conditions people trip over: your resident registration must be at the rented address, and the property must be within the size or value limits. Landlord consent is not required. Gather your lease, the transfer records showing rent paid, and your resident registration abstract, and submit them with your other deduction evidence.
Via employerWho: You, through your employer's year-end settlement or on HometaxJanuary–February
5
Model the flat-rate election
Foreign employees may elect a flat 19% on Korean employment income, roughly 20.9% with the local surtax, for a long window from your first day of work. It strips out every deduction, exemption and credit — including the rent credit — and excludes people with a controlling interest in the employer. It only wins at high salaries. Compare both each year.
Via employerWho: You, with your employer or a tax accountantElected annually
6
File the May global income return if you are not a single-salary employee
Freelancers, the self-employed, people with several employers and anyone with extra reportable income file between 1 and 31 May for the previous calendar year and pay by month end. Korean clients withhold 3.3% from freelance fees as a prepayment, not a final tax. Filing on Hometax is free and the tax office runs an English helpline on 126.
OnlineWho: You, or a licensed tax accountant1–31 May

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
Lease, rent transfer records and resident registration abstract, for the rent credit
Deduction evidence: pension and health contributions, medical, education, dependants
Treaty residence certificate from your home tax authority, if you are claiming a treaty article

Things most newcomers don’t know

The tax office is also where you protect your deposit, and almost no tenant makes the connection.

Since April 2023 a tenant whose deposit exceeds ₩10 million may inspect the landlord's unpaid national taxes at any tax office in the country — without the landlord's consent — from the moment the contract is signed until the lease start date, with only ID and a copy of the contract. Unpaid tax ranks ahead of your deposit at auction. In the city with Korea's worst per-capita jeonse-fraud record, treating that as a routine errand rather than an obscure right is the highest-value hour you will spend.

Source: National Tax Collection Act, as amended April 2023

The treaty article for professors and researchers is real, limited, and nationality-specific.

Several Korean double-tax treaties exempt remuneration for teaching or research at an approved institution for a fixed period. It is not automatic, it does not exist in every treaty, and its length and conditions vary. In a city where a large share of foreign arrivals are researchers, the difference between claiming it correctly and never hearing about it is a meaningful sum over a first contract — and it needs a residence certificate from your home tax authority.

Source: National Tax Service; PwC Worldwide Tax Summaries — Korea

Electing the flat 19% rate cancels the rent credit along with everything else.

The election replaces the progressive scale with a single rate on Korean employment income and forfeits every deduction, exemption and credit in exchange. That includes housing, medical, education and the monthly rent credit — and it generally cannot be combined with a treaty exemption either. On research and institute salaries it usually loses; run both numbers before electing anything.

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

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

Resident five years or fewer of the last ten and your overseas salary, investments and rental income sit outside Korean tax unless a Korean entity pays them or you remit them here. That is substantial planning space for anyone with assets abroad, and it closes silently. Knowing the exact date it closes is worth an accountant's hour in year four rather than a surprise in year six.

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

Common mistakes to avoid

Never claiming the monthly rent tax credit, or losing it by not having your resident registration at the rented address.
Assuming a professors-and-researchers treaty exemption applies without checking your own country's treaty text.
Electing the flat rate below its break-even and forfeiting the rent credit and any treaty relief.
Not tracking when the five-year foreign-income window closes.
US citizens forgetting 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.