Filing a Global Income Tax Return in Korea: Who Has to and How

Who has to file

If employment income is your only income and your employer completed year-end settlement, you generally do not file in May.

You do file if any of these apply:

• Business or freelance income, including income taxed at 3.3% withholding
• Rental income from property
• Financial income — interest and dividends — above the aggregation threshold
• Other income above the threshold, such as lecture fees or prize money
• Employment income from two employers that was not combined at settlement
• You missed year-end settlement, for example after leaving a job

The category that surprises people is freelance work. If a Korean company deducted 3.3% when paying you, that was a prepayment, not a final tax. The May return is where the actual liability is calculated and the difference refunded or collected.

Residency decides what is taxable

This is the question with the largest financial consequences for foreign nationals.

Resident — taxed on worldwide income Non-resident — taxed on Korean-source income only

Residency for tax purposes is not the same as your visa status. It turns on whether you have an address in Korea or have stayed 183 days or more in a tax year, assessed together with where your family, occupation and assets are centred.

So a foreign national who lives in Korea, works here and has family here is generally a resident, and their overseas rental income or dividends fall within the Korean tax net in principle.

Two things soften this:

• Tax treaties between Korea and your home country determine which country taxes what, and prevent the same income being taxed twice
• A foreign tax credit relieves tax already paid abroad

There is also a special rule limiting the scope of worldwide taxation for foreign nationals who have been in Korea for only part of a recent multi-year period. Because these interact, anyone with meaningful overseas income should get advice rather than guess.

Filing

Deadline: 1 May – 31 May, for the previous calendar year. Taxpayers subject to the diligent-filing confirmation regime have until 30 June.

How

• Hometax — the main route, with an English interface of partial coverage
• Sontax — the mobile app
• Tax office in person
• Through a licensed tax accountant (semusa, 세무사)

The National Tax Service sends a filing type notice, and taxpayers with simple affairs often receive a pre-filled return that needs only checking.

Documents that matter

• Withholding tax receipts from each employer
• Records of business income and expenses
• Evidence of foreign tax paid, if claiming the credit
• Personal deduction documents

Local income tax of 10% of your income tax is filed separately through Wetax, usually at the same time.

An English-capable tax accountant is a reasonable expense the first year if your affairs involve more than one country. The rules are not intuitive and the cost of a mistake compounds.

Missing the deadline

Late filing produces:

• Failure-to-file penalty
• Late payment penalty, calculated daily
• Loss of some deductions and reductions

A late return is still better than none — penalties are reduced the sooner you file, and if you never file the tax office may assess you on its own information, which will not include your deductions.

If a refund was due, you receive nothing unless you file. People with modest freelance income frequently skip filing on the assumption that no tax is owed, and in doing so forfeit a refund of the 3.3% withheld.

Correcting a filed return

• If you underpaid, file a revised return; earlier correction means smaller penalties
• If you overpaid, file a claim for correction. This can be made within five years of the statutory filing deadline, so an error found later is often still recoverable

Leaving Korea If you depart before the filing period with income requiring a return, arrange filing before you go or appoint a tax agent. Filing from abroad without Korean identity verification is difficult.