People take a midday stroll by the Cheonggye Stream in Seoul, April 23. Yonhap

Kang Min-ku, a 40-something CEO of a medium-sized manufacturing company in Jeonju, North Jeolla Province, thinks he belongs to the middle class, although he owns a business that hires more than 100 employees and pays their salaries on time.

"I don't think I make as much money as other CEOs from bigger companies or more promising industries," Kang said. "In addition, I only managed to own a home in Jeonju, but not in Seoul, where housing prices are far more expensive."

Kang is one of many Koreans who feel they are not as wealthy as what their income brackets suggest because their earnings fall short of their expectations in meeting the conditions used to determine social and economic classes, such as salary increase, home ownership and property value.

According to the Korea Development Institute (KDI), only 2.9 percent of the 3,000 adults identified themselves as upper class in a survey on social perception concerning the middle class.

"The finding is a surprise when considering the top 20 percent in the income bracket are generally categorized as upper class," KDI noted in the report.

In particular, only 11.3 percent of high-income earners with a monthly salary exceeding 7 million won ($5,100) said they are upper class. The other 76.4 percent identified themselves as middle class while another 12.2 percent responded that they are lower class.

Among those who are categorized as middle class, up to 40 percent said they can be categorized as lower class.

"The finding shows a huge gap between income, objective data and people's subjective judgment on which social and economic class they belong," the KDI said.

The institute assessed such a gap partly stems from a fall in disposable income among the top 20 percent of income earners.

Disposable income is money available from an individual's income after deducting taxes.

The top 20 percent income earners accounted for 40 percent of the country's entire disposable income in 2021, down from 44.3 percent in 2011.

On the other hand, those in the four lower income brackets saw their percentages increase over the 10-year period.

The rate went up from 5.3 percent to 6.7 percent for those in the bottom fifth, from 11.1 percent to 12.5 percent for those in the next 20 percent, from 16.3 percent to 17.3 percent for those in the middle group and from 23 percent to 23.5 percent for those in the second-highest group.

Regarding the middle class, those who have blue-collar jobs had a higher tendency than those with white-collar jobs to think of themselves as lower class.