South Koreans are set to become a year younger overnight after a law was passed to scrap the current traditional method of counting ages in a bid to simplify a centuries-old system.
Currently, babies in the country become one-year-old on the day they are born - and then get an additional year tacked on come January 1.
This means babies born on December 31 can age two years within hours.
The confusing system is due to end in June next year when citizens could have one or two years knocked off their ages on official documents.
Earlier this year South Korea's president-elect Yoon Suk-yeol promised to abolish the system, which critics say is an anachronistic, time-wasting custom and drags down an otherwise forward thinking nation.
The issue is further compounded as there are actually three ways to count age in Korea with each number recognised by different bodies.
The Western way (starting with '0' at the moment of birth and increasing by one year after every birthday); the 'year age', which starts with '0' at birth and adds one year at each 'year', and the 'Korean age' are all used in law, administration, and daily life.
For parents whose babies are born in December, it can be especially painful.
One hour after his daughter’s birth in the central city of Daejeon at 10pm on December 31 of last year, Lee Dong Kil posted the news on social media.
His friends immediately showered him with congratulatory messages.
“An hour later, when the new year began, they phoned me again to say congratulations for my baby becoming two years old,” said Mr Lee, who is 32 internationally but 34 in South Korea.
“I thought, ‘Ah, right. She’s now two years old, though it’s been only two hours since she was born. What the heck!'”
Why does South Korea use this confusing age system?
The origins of the traditional age-calculating system are not clear.
Being one-year-old at birth may be linked to the time a baby spends in its mother's womb or to an ancient Asian numerical system that did not have the concept of zero.
Another theory according to senior curator Jung Yonhak, at the National Folk Museum of Korea is that ancient Koreans cared about the year in which they were born in the Chinese 60-year cycle but, without regular calendars, did not celebrate the specific day they were born and instead marked another year of age on the day of the Lunar New Year.
This may have then shifted to the solar new year on January 1 as South Korea began embracing the Western calendar.
Is South Korea the only country to use this system?
Perhaps unsurprisingly, yes.
Neighbouring North Korea uses the Western age calculating system, but it follows its own calendar based on the birth of national founder and president-for-life Kim Il Sung.
Officially, South Korea has used Western-style calculations since the early 1960s.
But its citizens still embrace the old-fashioned system in their daily lives because the government has done little to get people to change over to the Western style.
Most South Koreans are simply accustomed to living with two ages.
How do people celebrate the anniversary of their birth?
People do not hold massive joint birthday parties on New Year’s Day; they just celebrate their birthday on the days they were born.
Young people consider themselves another year old on solar New Year’s Day (January 1) while older people often use the Lunar New Year’s Day.
Many family restaurants do not charge babies if they are 36 months old or younger, so parents often calculate their babies’ ages under the Western method when they are dining out.
What does it mean for people from abroad?
Many foreign journalists in Seoul ask Koreans what year and month they were born to calculate their Western age for news stories.
There are also some who say the concept of “Korean age” encourages a fixation on age-based social standing in this seniority-based country.
In South Korea, those born in the same year often treat each other as equals, while people must use honorific titles to address those born earlier, rather than directly using their names.
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