For most of its history, South Korea counted ages in a way that worked nothing like the system the rest of the world uses. A newborn was counted as one year old at the moment of birth. After that, everyone in the country gained a year together on January 1, no matter when they were actually born. Your birthday had nothing to do with how old you were.

Look at the extreme case and the oddness becomes clear. A baby born on December 31 was already counted as one. The next morning, when the calendar flipped to January 1, that infant became two. A child barely a day old was the same Korean age as a child born eleven months earlier.

Why the system existed

The traditional method treated time in the womb as part of a person’s life, so a baby was thought to arrive having already lived close to a year.

The New Year’s Day jump came from a different instinct: ageing as something everyone does together rather than alone. People turned a year older on the same day, instead of marking private birthdays scattered across the year. The system also carried real social weight. Anthropologist Mo Hyun-joo told Al Jazeera that “Age really matters” in South Korean culture, where age shapes how people speak to each other and where they stand in the social order.

One year or two, depending on the calendar

The gap between Korean age and international age was not always two years. It was one or two years, depending on whether your birthday had already passed that year. The gap reached two years only if your birthday had not yet come around. Once it passed, it shrank to one.

The “Gangnam Style” singer Psy is a clean example. Born on December 31, 1977, he was, by the figures reported when the law passed, simultaneously 44 in international age, 45 in calendar age and 46 in Korean age.

That third number points to something most coverage skipped: Koreans were not juggling two systems but three. There was also a “calendar age,” which counted from zero at birth but still added a year every January 1. As South Korean journalist Se-Woong Koo told Al Jazeera, “It’s tremendously confusing for many people; some people think of how old they are in terms of the Western way of counting, others do according to the Korean way of counting.”

What June 2023 changed, and what it didn’t

On December 8, 2022, the National Assembly changed the law. After a half-year grace period, the new rule took effect on June 28, 2023. From that date, international age became the standard for legal and official purposes.

Lawmakers framed the change in practical terms. Yoo Sang-bum, a member of the ruling People Power Party, told parliament the change was “aimed at reducing unnecessary socio-economic costs because legal and social disputes as well as confusion persist due to the different ways of calculating age.”

What the law did not do was switch off a lifetime of habit. The official count changed, but the everyday reflex didn’t follow it. Korean age is tied up with how people address each other and where they rank. Even a simple question about someone’s age can still draw on the old logic. Koo noted that “When you ask people their age, the answer Koreans usually give is their year of birth.”

The open question is how long both counts will live side by side. The law settled which number goes on a contract or a medical chart. It left untouched the number people reach for first when they meet, and that habit will shift more slowly than the law.