Why an age rule change could see South Koreans becoming a year younger overnight

South Koreans are set to become a year younger as the country's president-elect aims to simplify a centuries-old tradition

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.

South Korea's president-elect Yoon Suk-yeol has promised to abolish the system, which critics say is an anachronistic and confusing custom. 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.

Officially, South Korea has used Western-style calculations since the early 1960s but there has been little done by the government to encourage people to prioritise this version, its citizens still embrace the old-fashioned system in their daily lives.

While South Koreans are accustomed to living with more than one age, the move to abolish 'Korean age' has the backing of the country, with 71% in favour of the abolition of the Korean age, according to a recent survey.

• Why does South Korea use the strange 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 mothers’ womb or to an ancient Asian numerical system that did not have the concept of zero.

But becoming a year older on January 1 is even harder to explain.

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.

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.

Other Asian countries, including Japan and Vietnam, abandoned the Chinese-style age system amid an influx of Western culture.