'Korean age' abolished: How South Koreans became younger overnight

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Customers inside the new Apple Inc. store in the Gangnam District of Seoul, South Korea, on Friday, March 31, 2023. A new law makes people in the country a year or two younger Photographer: SeongJoon Cho/Bloomberg via Getty Images

Tens of millions of South Koreans instantly became a year or two younger Wednesday when a new law governing the country’s aging system took effect.

Before Wednesday, South Korea used three different systems to calculate ages, including one that means a baby born on December 31 could be 2 years old by the next day. It’s a practice President Yoon Suk Yeol, who took office in May 2022, promised to change.

A measure approved by South Korea’s parliament in December unifies the aging systems and adopts "international age" as its official way of calculating age.

"We expect legal disputes, complaints and social confusion that have been caused over how to calculate ages will be greatly reduced," Minister of Government Legislation Lee Wan-kyu said at a news briefing Monday.

Although the country has used the international age system – the one used by virtually everyone else – for legal and administrative purposes since 1962, Koreans have largely gone by their own system when determining how old they are.

The Korean age system

Babies in South Korea will no longer be 2 years old a day after theyre born after the country scrapped its unique aging system.(Photo credit should read JUNG YEON-JE/AFP via Getty Images)

Under the old Korean age system, a baby is 1 year old when they are born. According to a Korean embassy, one of the many theories on why is that the nine months spent in the womb are counted and rounded up. Others believe it could be tied to an ancient Asian numerical system that didn’t include zero.

Then, on January 1, everyone turns a year older, regardless of the date on which you were born. This means a baby born in December 2022 would turn 2 years old on Jan. 1, 2023.

But there is another way Koreans calculate age. Under this system, babies are 0 when born, but everyone turns a year older on January 1, regardless of the date on which you were born. This means a baby born in December 2022 would turn 2 on January 1, 2024, despite the baby’s birthday being in December. This system is currently used for military conscription in Korea.

The Korean embassy says some people think this system is tied to the 60-year Chinese calendar cycle, and that Koreans used that cycle because there were no regular calendars. Ancient Koreans used the first day of the lunar calendar to add a year, but later switched to January 1 when Koreans started observing western calendars.

Before this week, a person in South Korea could be three different ages.