Korea Global Income Tax: Last-Minute Deduction Checklist Before the May 31 Deadline

Korea’s Comprehensive Income Tax (종합소득세) deadline is May 31, 2026. If you’re a freelancer billing clients on a 3.3% withholding rate, running a side business, earning rental income, or holding multiple income sources in Korea, you need to file — and you need to file correctly.

The stakes are real: missing a single deduction can mean tens of thousands of won left on the table. Getting the numbers wrong can trigger a penalty that dwarfs any convenience you saved by rushing.

This guide is for English-comfortable readers — Koreans living abroad who must still file Korean taxes, foreign nationals who are Korean tax residents, and expats earning mixed income in Korea.

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The Core Distinction: Income Deduction vs Tax Credit

Before running through the checklist, understand the two categories Korea uses:

Income deduction (소득공제) shrinks your taxable income before the tax rate is applied. The personal exemption (인적공제) for dependents — 1.5 million KRW per qualifying person — works this way. At a 24% marginal rate, each dependent saves you 360,000 KRW in actual tax.

Tax credit (세액공제) cuts your final tax bill directly, regardless of marginal rate. Korea’s medical expense credit, education expense credit, and donation credit all work this way. A 15% credit on qualified medical costs means for every 1 million KRW of eligible spending, you save 150,000 KRW in tax.

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Dependent Exemptions: The Highest-Value Item to Check First

Every qualified dependent means 1.5 million KRW off your taxable income. The National Tax Service (NTS, 국세청) sets three requirements:

1. Relationship: Spouse, children (under 21), parents (60+), siblings (under 21 or 60+), or disabled dependents at any age
2. Annual income: The dependent’s total income must not exceed 1 million KRW (or total employment income under 5 million KRW)
3. Financial support: You must be providing financial support — co-residence is not strictly required

Common misses for people with Korean-source income:

• Parents earning small rental income → check if it pushes them over the 1 million KRW threshold
• Claiming a dependent already listed on a sibling’s return → duplicate claims are rejected and penalized
• Children studying abroad → co-residence rule relaxed, but financial support must be documented

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Medical Expense Tax Credit

The threshold for medical expense credits in Korea works as a percentage of your income. You only get a credit on the portion of medical spending that exceeds 3% of your earned or business income amount. Spending below that threshold earns you nothing.

The standard credit rate is 15% on qualifying amounts. Higher rates apply to fertility treatments (난임시술) and to expenses for disabled or elderly dependents (65+).

What qualifies

• Hospital, clinic, dental, and oriental medicine (한의원) fees
• Prescription medication
• Hearing aids and disability assistive devices
• Glasses/contacts up to a per-person cap
• Postpartum care center costs (if income is below a set threshold)

What does NOT qualify

• Any amount reimbursed by private health insurance (실손보험) — you must subtract these even if Hometax shows the full amount
• Cosmetic procedures not medically required
• Health supplements, vitamins, fitness club fees

For verified current limits and rates, check the NTS Hometax site at hometax.go.kr or the NTS English portal at nts.go.kr.

Related: Understanding Korean Tax Penalties →

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Education Expense Tax Credit

Unlike some countries’ tax systems, Korea allows the taxpayer themselves (not just parents) to claim education credits. If you’re a freelancer attending night school, a cyber university, or a vocational training program, your own tuition is fully creditable at 15% with no cap.

Dependent children’s education

Korea distinguishes by school level: pre-school, elementary through high school, and university. Each has a different cap. The Hometax system usually auto-populates data from schools that report electronically, but:

• Private tutoring (학원) is only creditable for children under school age (취학 전)
• Overseas tuition is generally not creditable
• Uniforms (교복) are creditable for middle and high school students up to a per-student cap

If a school or institution didn’t report electronically, you must manually enter the amount and keep your receipts for five years.

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Donation Tax Credit: Check Carryovers First

Korea allows tax credits on qualifying donations:

• Statutory donations (법정기부금): to the government, national defense funds — deductible up to 100% of income
• Designated donations (지정기부금): to social welfare organizations, cultural groups, religious institutions — up to 30% of income (10% for religious organizations)

The standard credit rate is 15% on amounts up to 10 million KRW and 30% above that. Verify current figures at nts.go.kr.

Critical step: if you made large donations in prior years that exceeded the annual deduction cap, up to 10 years of carryforward is allowed. In Hometax, go to 조회/발급 → 기부금 이월 현황 to check remaining carryforward balances before filing.

Related: Freelancer Tax Strategy — Advanced →

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Using Hometax: Don’t Submit the Draft as-Is

The NTS provides an automated “easy filing” (간편신고) service that pre-populates most data from income withholding reports. It’s a useful starting point — not a finished return.

Before submitting, manually verify:

1. Income section: Does it capture all sources? Freelance invoices, YouTube/creator income, rental income, investment income above the threshold?
2. Deductions section: Are medical, education, and donation amounts complete? Items not reported electronically won’t appear automatically.
3. Dependents: Is the income test accurate for each listed dependent?
4. Business expenses: Self-employed filers need to enter qualifying business expenses either via actual books (장부신고) or standardized estimation (추계신고).

The NTS English page at nts.go.kr has a foreigner-specific guide each filing season. If your Korean is limited, look for the “외국어 서비스” section or call the NTS foreign language helpline.

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Late Filing Penalties

Miss the May 31 deadline and you face:

• Failure-to-file penalty: 20% of unpaid tax (40% for fraudulent non-filing)
• Late payment interest: Accrues daily on unpaid tax

If you’re due a refund, you won’t face these penalties — but there is a 5-year statute of limitations on claiming refunds. Even if you missed previous years, it’s worth checking if prior returns are worth amending.

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When to Hire a Korean Tax Accountant (세무사)

DIY Hometax filing works well if your income is straightforward. Consider professional help if:

• You have both employment income and business income
• You have Korean rental income or overseas rental income
• You received stock options or equity compensation
• Your income changed significantly year over year
• You are a foreigner uncertain about tax residency classification

Bilingual tax accountants are readily available in major Korean cities and online. Fees typically start around 100,000–200,000 KRW for simple returns. The NTS also provides a free filing assistance service each May at many district tax offices (세무서).

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The May 31 deadline sounds distant but isn’t. One overlooked deduction — a dependent you forgot to claim, a year of donations you didn’t carryforward — can mean a real refund you’ll never see. Open Hometax now, check the draft, and work through the list above.