Side Income in Korea: Do You Have to File Global Income Tax? (2026)

Once you've made a few million won on the side in Korea, an uneasy question creeps in: "Do I have to report this? Will my employer find out? The 3.3% was already withheld — isn't that the end of it?" All three are common misunderstandings.

Here's the short version. If your side income is business income (online store, blog/YouTube, freelance work), you must file regardless of the amount. If it's "other income" (one-off lecture or writing fees), you file only when it exceeds ₩3 million a year. And that 3.3% isn't a final tax — it's tax paid in advance, so filing often gets you a refund. Your employer isn't automatically notified.

Am I required to file — business income vs. other income

Everything hinges on whether your side income is "business income" or "other income."

• Business income — earned continuously and repeatedly: online stores, an actively run blog/YouTube, freelance contracts. You must file no matter the amount.
• Other income — one-off earnings like an occasional lecture or writing fee. After a 60% deemed-expense deduction, you must file only if the remaining "other income" exceeds ₩3 million a year; below that you can settle it as separate taxation.

One warning: "I didn't register a business, so I don't need to report" is a myth. The tax office automatically receives settlement data from Naver, Coupang and Google (AdSense), so repeated earnings count as business income even without registration.

"But 3.3% was already withheld — I have to pay again?"

The 3.3% taken from freelance/side income is not a final tax — it's prepaid (a provisional amount). Your real tax is settled in the May filing, after your expenses and deductions are applied.

So if you had meaningful expenses or modest income, the 3.3% already paid often exceeds your actual tax — and you get money back. Filing usually isn't "paying more"; skipping it is "leaving a refund unclaimed."

Will my employer find out?

You file the tax return yourself on Hometax, so it isn't reported to your employer automatically. That said, higher income can raise your health-insurance premium, which is where an employer might notice. If that worries you, you can pay the extra premium separately yourself rather than through payroll to reduce exposure.

When and where to file

• When — each May for the previous year's income (for 2026, by June 1, extended a day because May 31 is a Sunday).
• How — Hometax (hometax.go.kr) or the Sontax app. If you received a "modu-chaeum" pre-filled notice, most fields are already completed.
• Combined — file your salary (from year-end settlement) together with side income. Tax already paid (settlement + the 3.3%) is credited as prepaid tax.

What if I don't file — or already missed it?

If you were required to file and didn't, expect a non-filing penalty (20% of the tax, 40% if fraudulent) plus a late-payment penalty. Conversely, if you missed a past filing or a deduction, you have 5 years to claim it back via a "correction claim."

Ways to lower the tax

• Keep expense records — a work laptop, software, phone/internet and transport can count as expenses. Save card, cash-receipt and transfer records.
• Use deductions — national pension and health insurance, pension savings/IRP, and the Noran Umbrella mutual-aid fund all reduce tax.

FAQ

Do I file even if I only make ₩500k a month on the side?

If it's business income with 3.3% withheld, yes — regardless of amount. You may even get a refund, so check.

What about blog/YouTube earnings?

If run consistently for ad revenue, it's business income (file regardless of amount). A rare one-off from a hobby may qualify as "other income."

Are Korean stock trading gains taxable?

For ordinary individuals, gains on listed Korean stocks are generally tax-exempt, so usually not part of this filing. But if interest/dividend income exceeds ₩20 million a year, that's separately in scope.

The 3.3% isn't the end — it's an advance. One May settlement usually gets most of it back, and at minimum spares you the penalties.

This is general information for 2026 (2025 income) and not tax advice. Your situation may differ — confirm specifics on Hometax or with a tax professional.