I am thirty-five years old. I think.
That’s not a joke. Since Korea officially switched to the international age system in 2023, I’ve genuinely lost track. For most of my adult life, I operated on Korean age — the system where you’re born as a one-year-old and gain a year every January 1st, regardless of when your birthday falls. I knew my Korean age instinctively, the way you know your own name. Then the government changed the rules, and now I’m somewhere in my mid-thirties, and I’ve just… stopped counting.
My daughter has the same problem, except she’s two. Or three. Depending on who you ask.
Her grandmother calls her 세 살 (se sal) — three years old. Her paediatrician at the clinic in Siheung writes down two. At her last check-up, the nurse and my mother-in-law had a polite but firm disagreement about this in the waiting room while my daughter sat between them, completely unbothered, eating a rice cracker.
I didn’t intervene. I’ve learned not to.
A Number That Starts Before You’re Ready
To understand why Korea had two age systems — and why switching away from one of them has caused more confusion than it solved — you need to understand how Korean age actually works.
In the traditional Korean age system, called 세는나이 (seneun nai), everyone is considered one year old at birth. The logic, loosely, is that the time spent in the womb counts. You’ve already existed for approximately nine months by the time you arrive, so zero feels wrong. One feels more honest.
Then, on January 1st — not on your birthday — everyone in the country turns a year older together. It’s a collective birthday of sorts. The whole nation ages simultaneously.
This means the gap between Korean age and international age isn’t fixed. It shifts depending on when your birthday falls in the year. If you were born in late November, you might be internationally zero years old for only a matter of weeks before Korean New Year flips you to two. A baby born on December 31st is one year old at birth, and two years old the following morning.
When I try to explain this to British friends, the reaction is always the same. First, a pause. Then: “So you’re telling me a baby can be two years old after one day?”
Yes. That is exactly what I’m telling you.
The System That Made Sense (Until It Didn’t)
Growing up in the UK from primary school, I learned to navigate two versions of myself. At school, I was the international age — straightforward, tied to my birthday in the way everyone else’s was. On the phone to relatives in Korea, I was a year or two older. I switched between them without thinking, the way you switch languages.
The confusion only happened when I had to explain it out loud.
“How old are you?” a classmate would ask.
“Eleven,” I’d say. “But in Korea I’m twelve.”
“Why?”
And then I’d have to explain the whole system — the birth year, the January reset, the womb logic — to someone who had never considered that age might work differently anywhere. It never landed cleanly. People understood the mechanics eventually, but they never quite accepted it as reasonable. The idea that age could be a social convention rather than a precise biological fact didn’t sit well with the British sense of order.
What I didn’t realise then was that Korea itself wasn’t entirely consistent. Alongside 세는나이, there was also 만나이 (man nai) — the international system, used in legal and medical contexts — and a third system called 연나이 (yeon nai), which calculated age simply by subtracting your birth year from the current year. Three systems, running simultaneously, each used in different contexts. Doctors used one. Government documents used another. Grandmothers used a third.
The 2023 Change That Changed Everything (Sort Of)
In June 2023, the Korean government officially standardised age calculation. From that point, all official and legal contexts would use 만나이 — the international system, tied to your actual birthday.
On paper, this was a simplification. In practice, it created a new layer of confusion for anyone who had spent decades thinking in 세는나이.
I was in my mid-thirties when it happened. I had known my Korean age for so long that the adjustment felt genuinely disorienting — not because the number was dramatically different, but because I no longer trusted my instinct. I’d reach for my age in conversation and find myself calculating. Subtracting. Double-checking.
I’ve since settled on thirty-five. I think that’s right. I’ve stopped verifying.
My wife, who is Korean and pregnant with our second daughter — due in September — has the same issue. She knows roughly how old she is. But ask her on the spot and she’ll pause in a way she never used to.
What This Means at the Playground
The generational divide is where it gets genuinely interesting.
Older Koreans — grandparents, people in their sixties and above — largely continue to use 세는나이 in daily conversation. It’s not defiance. It’s simply the system they’ve used for their entire lives, embedded in the language and the way they relate to one another. Changing it officially doesn’t automatically change the instinct.
Younger Koreans, particularly those in their twenties and thirties, are more likely to use 만나이 now — or at least to be aware of the distinction. But even they slip back into the old system with family, or when speaking formally to elders, where using the wrong age might feel disrespectful.
My daughter sits in the middle of all this. When I take her to the playground near our apartment complex in Yongin, the grandmothers on the bench will ask her age. I’ll say two. They’ll nod and mentally add one. Everyone understands the situation. Nobody says anything.
It’s a negotiation dressed up as a simple question.
Why It Still Matters
Age in Korea isn’t just a number. It’s a social coordinate.
Korean culture — shaped significantly by Confucian ideas about hierarchy and respect — uses age to determine how people speak to each other, how they address each other, and what obligations exist between them. The honorific language system, 존댓말 (jondaemal), is calibrated partly by age difference. Whether you use formal or informal speech often depends on whether someone is older than you, younger than you, or the same age.
This is why Koreans often ask each other’s age early in a conversation — not out of nosiness, but because it’s genuinely necessary information for how the conversation should proceed. My daughter already knows this. At twenty-four months old — internationally — she calls the older girl next door 언니 (eonni), older sister. She didn’t need to be taught. She picked it up from the environment.
When age is this socially significant, having uncertainty about the number creates a small but persistent friction. The 2023 reform was sensible and practical. But it introduced a transitional awkwardness that Korea is still working through.
Two Ages, One Country
Korea isn’t unique in having a complex relationship with age — many East Asian countries have used similar systems historically. But the current moment in Korea is particularly interesting because the country is visibly mid-transition. Two systems coexist, informally. People navigate between them depending on context and audience.
If you visit Korea and someone tells you their age, it’s worth asking which system they mean. Not because you need the precise number, but because the question itself opens a door into something genuinely interesting — a culture grappling with the tension between tradition and standardisation, between what has always felt true and what the government has now officially declared correct.
My daughter is two years old. Internationally.
She has no idea there’s any other option. By the time she’s old enough to explain the system to a confused friend, I suspect Korea will have fully settled into 만나이, and the whole thing will feel like a historical curiosity rather than a lived confusion.
Until then, I’m thirty-five. Probably.
If you enjoyed this post, you might also like why everyone in Korea calls each other Unnie and Oppa — the age-based social system that makes Korean age so important — or why Koreans bow to their elders on New Year’s Day, respect and hierarchy in its most visible form.
Inside The Haru Box
The Haru Box explores everyday life in Korea through small cultural details and daily habits. Written by David — Korean-born, raised in England, now living in Yongin, South Korea with his wife and daughter. These are the moments that make life in Korea feel real.