When May arrives, the filing season for comprehensive income tax in Korea, accountants frequently encounter clients asking, "I've already paid all my taxes — why do I have to pay again?" This question comes up especially often from those who, after years of salaried employment, earn business income for the first time. Let's examine what lies behind this confusion through a single case.
Mr. A served as an executive at a company last year and earned 200 million won in wage income. Due to personal circumstances, however, he retired in September last year and subsequently leveraged his accumulated expertise to participate in projects at an acquaintance's company. Through such freelance activity, he earned 150 million won in business income.
Mr. A entrusted a tax agent with filing the additional comprehensive income tax due this May. But he was stunned to learn that the comprehensive income tax came to roughly 50 million won. "I've already paid taxes on 200 million won in wage income through withholding and year-end settlement," he said. "Just because I had an additional 150 million won in income, do I really have to pay 50 million won more?"
This kind of situation is one that those earning business income for the first time often encounter. There are two main reasons for the bewilderment.
The first concerns how business income is paid. Wage income is automatically withheld each month according to a simplified tax table whenever salary is paid. This is precisely why salaried workers find it difficult to grasp how much tax they are actually paying. The year-end settlement is merely a process of reconciling the difference between taxes prepaid in this manner and the taxes actually owed. Business income, by contrast, requires aggregating an entire year's profits and filing and paying all at once in May of the following year. Because the structure does not allow taxes to be spread out monthly, the tax contained in a single bill feels uniquely large and sudden.
The second is the trap of the progressive tax structure. Korea's income tax operates on a progressive system that applies higher rates to larger incomes. Mr. A's 200 million won in wage income, during the year-end settlement, sequentially filled the rate brackets starting at 6 percent and rising through 15 percent, 24 percent, 35 percent, and 38 percent. The problem is that when 150 million won in business income is added on top, after deducting necessary expenses of 20 to 30 percent, a high rate of 38 to 40 percent is applied. This is because the wage income has already filled the lower rate brackets. Even with the same 150 million won, had it all been received as wage income, it would have been taxed sequentially from the lower brackets. But additional business income is taxed at high rates from the outset, making the tax burden far heavier than expected.
This is precisely the essence captured in the name "comprehensive income tax." Because various types of income — wage, business, financial, and other income — are "comprehensively" combined into a single tax base, the impact of the progressive rate is magnified as different categories of income are summed and grow larger. Therefore, when business income newly arises, it is more important than anything to understand in advance how one's overall income structure will change.
When business income exists alongside wage income, it is essential to develop the habit of estimating the projected tax in advance and preparing accordingly. If May's tax bill comes as a shock, it is most often the result of failing to prepare ahead of time. Taxes are an unavoidable obligation, but they can be sufficiently managed by understanding the principles of income structure and progressive taxation and planning in advance. Rational tax planning is the first step toward fully preserving income that has been legitimately earned.
