Unless you’re Korean, it’s unlikely you’re celebrating two birthdays in a year.

The idea is simple, but it’s something I struggled to fathom as a seventh-grader in a Korean-administered high school. At the time, a friend named Ahn tried his best to explain how it works, but I was too preoccupied to explore the why behind it.

See, having two birthdays every year is official in South Korea. One is the individual’s actual day of birth, of course, while the other is the Korean birthday, which falls on the Lunar New Year and is celebrated by everyone.

To illustrate how this aging system differs from convention, it must first be noted that a Korean is already one year old right after birth.

So for an example, If a baby is born on Feb. 15, 2018, he or she will be two years old in the Lunar New Year, which falls on the day of the second new moon after the winter solstice — Feb. 16, 2018. In this case, a 2-year-old in Korea is only 1 day old for everyone else.

According to Quartz, this method of age calculation traces its origins in China, but South Korea is the only country that continues to use it today. If you want to know yours, a more direct approach is to take the current year, subtract your birth year and add one.

The Korean birthday is called eumnyeok saeng-il, a communal affair that highlights the country’s emphasis on collectivity. It also isolates age as a highly important concept reflected in the organization of social relationships. Needless to say, it’s crucial to respect elders in society.

Traditional celebrations commemorate ancestral spirits who are given food as an offering. Juniors offer sebae, a deep formal bow, to their seniors. In return, they are given gifts and money considered to bring good fortune. Families spend the rest of the day eating, playing games and storytelling.

With its cultural significance, eumnyeok saeng-il is considered to be more important than yangnyeok saeng-il, or the individual’s actual birthday. Nonetheless, both can be used in regulations of different settings, whichever applies.

For instance, in things like the age of marriage consent and commencement of primary school, the actual age is used. But in matters such as buying a car or video games, the Korean age applies, according to Atlas Obscura.

An individual’s actual birthday goes pretty much like everywhere else. However, big celebrations are held on the first and 60th birthdays, marking key ages of survival based on history. Dol, is the Korean traditional celebration of a 1-year-old’s birthday

Add One On in Korea