Korean Tax Penalty Calculator

This calculator works out the penalty tax added on top of the tax itself when a return was not filed by the deadline, was filed for less than the true amount, or the tax was not paid on time. Penalty tax is not a fine; it is assessed as part of the tax, and it comes in two kinds. One is the filing penalty for not filing or under-filing, the other is the late-payment penalty that accrues for each day the tax stays unpaid. Enter the tax underpaid, the months since the filing deadline and the days since the payment deadline, and the calculator shows both penalties separately and the total due including the tax.

Its real use is answering "how much do I save by filing now". The 국세기본법 reduces the filing penalty for people who come forward on their own, and the reduction shrinks the longer they wait. Many people do not know that timetable, sit tight, and lose the reduction entirely.

People who forgot the May comprehensive income tax return, missed a capital gains preliminary return, or filed and later discovered that some income was left out. Comparing "what it costs to file now" with "what one more month adds" gives an immediate answer.

Someone who has received a tax audit notice uses it for the opposite reason: to confirm that no reduction remains. A return filed after learning that an assessment or correction is coming does not count as voluntary, so the time to act is before the notice arrives. People abroad can still file a late or amended return, and appointing a tax agent lets it be handled from outside Korea.

Filing penalties are set by 국세기본법 제47조의2 and 제47조의3. Non-filing costs 20% of the tax due and under-filing 10% of the shortfall; where there is fraudulent conduct such as double books or false documentation, both rise to 40%. The late-payment penalty under 제47조의4 multiplies the unpaid tax by 0.022% per day (22 per 100,000 under 시행령 제27조의4) and by the number of days late, which is 8.03% a year.

The reductions are in 제48조제2항. If you file on your own after the deadline, a share of the filing penalty is waived. For a late return after non-filing, it is 50% within 1 month, 30% within 3 months and 20% within 6 months, then nothing. For an amended return after under-filing it is more generous: 90% within 1 month, 75% within 3 months, 50% within 6, 30% within 12, 20% within 18 and 10% within 24 months. The order is: multiply the tax by the filing penalty rate, take off the reduction, then add the late-payment penalty separately. The late-payment penalty is never reduced.

Take the calculator's default: ₩10,000,000 of tax that was never filed, one month past the filing deadline and 30 days past the payment deadline. The non-filing penalty is 20%, or ₩2,000,000, but because the return is filed voluntarily within 1 month, 50% is waived and ₩1,000,000 remains. The late-payment penalty is ₩10,000,000 × 0.022% × 30 days, or ₩66,000. The penalties total ₩1,066,000, and with the tax itself the amount due is ₩11,066,000.

Had the same person waited seven months, the reduction would be gone, the full ₩2,000,000 would stand, and 210 days of late-payment penalty would add ₩462,000, for ₩2,462,000 in penalties alone. By contrast, someone who filed but understated the tax by ₩10,000,000 and amends within a month pays the 10% under-filing penalty of ₩1,000,000 less a 90% reduction, leaving ₩100,000, plus ₩66,000 for late payment, ₩166,000 in all. That gap is why filing something on time matters so much.

The first is thinking "I am late anyway, I will sort it out later". The reduction starts falling the moment 1 month passes, and for non-filing it disappears entirely at 6 months. The second is treating filing and payment as the same thing. Filing without paying leaves the late-payment penalty accruing every day, so paying quickly matters as much as filing quickly. The third is expecting the reduction to apply to the late-payment penalty. It applies to filing penalties only.

The fourth is filing after an audit notice and expecting a reduction. A return filed after the notice is not voluntary and gets none. The fifth is taking a narrow view of fraud. Where there are signs of double books, fabricated documents or hidden assets, the rate jumps to 40% and the assessment period grows longer. Double-entry bookkeepers and companies are also subject to a separate revenue-based calculation, with the higher figure applying, and taxes such as VAT carry their own penalties; none of that is included here.