For decades, if you asked someone in South Korea how old they were, the honest answer required a follow-up question: 'Korean age, or international age?' As of June 28, 2023, that ambiguity officially ended — South Korea passed legislation standardizing on international age for all legal and administrative purposes, retiring a centuries-old counting system that had made Koreans one and sometimes two years 'older' than the rest of the world by simple calendar convention.
This article explains exactly how traditional Korean age worked, why South Korea abolished it, how it differs from the separate (and still-used) Chinese age system, and what age you'd actually be under each system today.
How Traditional Korean Age ('Se') Actually Worked
Under the traditional system, called se in Korean, everyone was considered one year old at the moment of birth, not zero — counting the time in the womb as a first year of life. Then, critically, everyone's age increased by one on New Year's Day (January 1st), not on their individual birthday.
| Birth Scenario | Traditional Korean Age Result |
| Born January 1 | Turns 2 the very next day |
| Born December 31 | Turns 2 the very next day (same as above) |
| Born mid-year (e.g. June) | Turns 2 the following January 1, at roughly 6-7 months old |
This produced the system's strangest, most-cited quirk: a baby born on December 31st was considered 1 year old at birth, and then turned 2 years old the very next day, on January 1st — at barely 24 hours of actual life. Meanwhile, someone born in January would have to wait almost a full calendar year before their first 'age up.' Two babies born a day apart, on either side of a New Year, could be considered a full year apart in age despite almost no actual difference in how long they'd been alive.
Why South Korea Abolished It in 2023
The push to standardize on international age had been building for years before the 2023 law, driven by a mix of practical and cultural pressures. Administrative confusion was a major factor: Korean age, international age, and a third system called 'counting age' (used for some specific legal purposes, like alcohol and tobacco eligibility, which counted from the calendar year of birth rather than the exact date) were all in simultaneous, overlapping use across different contexts — insurance contracts, medical records, and legal documents frequently required clarifying which age system applied, creating genuine friction in daily bureaucratic life.
There was also a cultural and public-health dimension: some policymakers and citizens argued the traditional system contributed to age-based social hierarchy pressures already prevalent in Korean workplace and social culture, where being even one nominal year 'older' can carry real social weight in a culture with strong age-based speech and etiquette norms. Standardizing to international age was framed partly as reducing unnecessary friction in these dynamics, alongside the straightforward administrative simplification.
The legislation, passed by South Korea's National Assembly and taking effect June 28, 2023, mandated international age for all official documents, medical records, and most legal purposes, effectively ending the everyday use of the traditional se system within a single legislative act, though the cultural habit of using Korean age in casual conversation persisted for a transitional period afterward.
Korean Age vs. Chinese Age: Similar, But Not the Same
It's a common misconception that Korean age and Chinese age are the same system — they share a root concept (counting birth as age one) but differ in exactly when the age-up occurs, which matters a great deal for anyone comparing the two.
| System | Starts at Birth? | Age Increases On | Still Officially Used? |
| Traditional Korean Age | Yes, age 1 at birth | New Year's Day (January 1) | No — abolished for official use in 2023 |
| Chinese Age (Sui) | Yes, age 1 at birth | Lunar New Year (varies each year) | Yes, still used informally, especially for cultural/traditional purposes |
| International Age | No, age 0 at birth | Individual birthday | Yes, the global standard, now including South Korea |
The key distinction: Korean age (before 2023) ticked over on the fixed solar calendar's New Year, January 1st, while Chinese age still ticks over on the Lunar New Year, which shifts date each year (typically late January to mid-February). This means two people born on the same day, one counted under the old Korean system and one under the Chinese system, could still end up at slightly different 'traditional ages' in any given year depending on where the Lunar New Year fell relative to their birthday. For a deeper look at the Chinese age system specifically, see our global age-counting comparison.
What Age Would You Be Under Each System?
Since South Korea's 2023 law, this is now mostly a historical curiosity rather than a live calculation anyone needs for official purposes in Korea — but it remains genuinely useful for understanding older Korean media, historical documents, or conversations with older relatives still mentally accustomed to the traditional system. As a rough rule of thumb: take your international age and add one or two years, depending on whether your birthday has occurred yet in the current calendar year, to estimate your old-style Korean age.
A Reminder of How Unusual Age-Counting Conventions Are Worldwide
Korean age is just one of several genuinely different age-counting conventions used historically around the world — Japan used an extremely similar system until standardizing on international age much earlier, in 1950, and Vietnam has historically used a comparable convention as well. For the fuller global picture, including how these systems compare to Western age-counting, see our complete guide to how different cultures calculate age.