Who must file an income tax return in South Korea, the tax year and deadline, what documents you need, how to file with National Tax Service (NTS), and what happens if you are late.
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Updated for 2026
Last reviewed September 2026
This is the general edition of this guide for South Korea. It explains how the Business registration number, VAT and annual filing work and names National Tax Service (NTS) as the place to confirm thresholds and dates. Country-specific figures are added as each edition is reviewed.
Who must file
In most countries, anyone with income above the tax-free amount who was not fully taxed through payroll withholding must file: the self-employed, landlords, company directors and anyone with more than one income source. Companies file their own return. Check National Tax Service (NTS)'s rules for employees, who are sometimes exempt or auto-assessed.
Tax year and deadline
Every country fixes a tax year and a filing deadline a few months after it ends. National Tax Service (NTS) publishes both. Put the deadline in your calendar with a reminder a month before, because late filing is penalised even when no tax is due.
What you need
Your Business registration number and login for National Tax Service (NTS)'s online service.
Employment income statements from each employer showing pay and tax withheld.
Your invoices, bank statements and expense records if you are self-employed.
Certificates for pension contributions, insurance, donations and other reliefs you will claim.
Last year's return, to check nothing is missed.
Filing step by step
Log in to National Tax Service (NTS)'s online service and open the return for the year.
Check any pre-filled income against your own records and add anything missing.
Enter business income and allowable expenses, then reliefs and deductions with the supporting figures.
Review the calculation, submit, and save the acknowledgement. Pay any balance by the payment deadline.
Employees and salary tax
Employers in South Korea withhold income tax from salaries and pay it to National Tax Service (NTS). Keep your payslips and the annual statement; the return reconciles what was withheld against what is due, and refunds arise when too much was taken.
If you are late
Late returns attract a fixed penalty and late payment attracts interest, both set by National Tax Service (NTS). File even if you cannot pay in full; penalties for not filing are usually heavier than for paying late, and most authorities allow instalment plans.
Questions people ask
Do I need to file if my employer already deducted tax?
It depends on South Korea's rules. Some countries require every taxpayer to file, some auto-assess employees, others exempt employees with a single employer and no other income. The rule for South Korea is set out above.
What if I had no income?
If you are registered with National Tax Service (NTS), you may still have to file a nil return. Failing to do so is treated as a late return in many countries.
Can I file late without a penalty?
Rarely. Some authorities allow an extension if requested before the deadline. Otherwise file as soon as possible; penalties often grow with time.
Should I use an accountant?
If you are employed with no other income, the online service is designed for you. If you run a business or have foreign income or property, an accountant usually saves more than the fee.
Sources
National Tax Service (NTS) — the official guidance for South Korea
How this guide was made
Written from published tax-authority guidance and reviewed on 2026-09-03. Everything here is indicative rather than a ruling on your circumstances, and rules change. Confirm anything you rely on with National Tax Service (NTS) before acting on it, and tell us if you find something out of date so we can correct it.
This guide explains the rules in general terms and is not tax advice for your circumstances. Confirm your position with a qualified adviser or with National Tax Service (NTS).
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