US tax for Americans in South Korea

A treaty and a totalization agreement, doing separate jobs

The US–Korea income tax treaty addresses double income tax; the totalization agreement addresses double social security by assigning your coverage to one system. An American on a Korean payroll with Korean coverage generally escapes US self-employment tax on that work, and a certificate of coverage is the evidence rather than an assumption.

The teaching article is narrow, and it is claimed far too widely

The treaty's teaching and research provision is the single most over-claimed position I see on Korean returns. It is narrow in scope, time-limited, and aimed at a particular kind of invited academic engagement. It does not exempt an ordinary school or hagwon salary, and claiming it where it does not apply creates a position that has to be defended rather than simply filed.

The exclusion or the credit is what actually handles a teaching salary — and for a first-year arrival, the exclusion often wins outright.

The 19% flat election, and what it does to your credit

A foreign worker in Korea can elect a flat national rate of 19% on employment income — around 20.9% with the local surtax — instead of the progressive table, for up to twenty years from the start of Korean employment, provided that employment began by the end of December 2026. Choosing it gives up Korean deductions and credits, and it applies to employment income only.

On the US side the election is not neutral. A lower Korean rate means less Korean tax paid, which means a smaller foreign tax credit — and for a high earner that can turn a year in which the credit covered everything into a year with US tax to pay. The Korean saving and the US cost have to be weighed together rather than separately.

First-year arrivals: the exclusion often wins

Someone who arrives mid-year on a teaching contract is taxed lightly in Korea for those first months, which leaves little Korean tax to credit. The Foreign Earned Income Exclusion, $130,000 for tax year 2025, frequently covers the whole of that part-year salary and produces a cleaner result than Form 1116 would.

That reverses as income and Korean tax rise. It is a genuine year-by-year comparison, which is why a default answer is the wrong answer here more often than in most countries.

Retirement allowance at the end of a contract

Korean law entitles an employee with at least a year of continuous service to a retirement allowance of roughly thirty days' average wage for each year worked. Korea taxes it under a separate regime from ordinary salary; the US treats it as compensation for services performed abroad, attributed to the years in which it was earned.

Because the two systems tax it differently and often in different years, it is the item most likely to produce a credit-timing mismatch on a Korean return.

A worked example, tax year 2025

A single American engineer employed in Seoul on salary equivalent to $135,000, with Korean income tax and local surtax of $28,350 for the year, claiming the credit.

IRC §901, §904, §911 and §1401; US–Korea income tax treaty, including the teaching and research article; US–Korea totalization agreement; Korean flat-rate election for foreign workers; Korean Labor Standards Act on retirement allowance; IRS Publication 54; IRS Publication 514; Rev. Proc. 2025-32; 31 CFR 1010.350. US figures are tax year 2025. Checked 22 September 2026.