South Korea is the most prominent country associated with starting age at 1, a practice shared historically with China, Japan, and Vietnam. In this system, a newborn is considered one year old immediately after birth because the time spent in the womb is counted as the first year. While South Korea has officially adopted the international standard for legal purposes, the traditional method still holds cultural weight in everyday social interactions.
Why newborns count as one year old
The logic behind this system is not mathematical error but a different perspective on time. Rather than measuring elapsed time from the moment of birth like a stopwatch, the East Asian approach treats age as an ordinal position. You are in your first year of life, so you are one. This mirrors how a book starts at Chapter 1, not Chapter 0.
Historically, this was tied to lunar calendars and agricultural cycles. Since exact birth dates were less critical in agrarian societies, groups of people born within a similar period were often considered the same age. Counting the gestational period ensured that everyone born in the same year, regardless of the specific month, started on the same footing.
How the traditional Korean system worked
Until recently, South Korea used a unique method called Sebeom. In this system, every person in the country aged up by one year on January 1st. Birthdays did not trigger an age increase. If you were born on December 30th, you were one year old at birth and turned two on January 1st of the following year, just 24 hours later.
This created a situation where individuals could have three different ages depending on the context:
- Korean Age: The traditional social age, where you are 1 at birth and age on New Year's Day.
- International Age: The standard global counting system, where you are 0 at birth and age on your birthday.
- Counting Age: A legal metric used for specific regulations like military conscription and driving licenses, which sometimes followed a different rule set.
The shift to international standards
The coexistence of three age systems caused significant administrative friction. Disputes arose in pension claims, legal liabilities, and social security benefits when individuals and the state disagreed on official age. To resolve these inconsistencies, the South Korean government passed legislation in 2023 mandating the use of the international standard for all official documents and legal contexts.
President Yoon Suk-yeol made this change a campaign promise, arguing that the traditional system created unnecessary bureaucratic costs and confusion in a globalized economy. However, cultural habits are slow to change. In casual conversation, many Koreans still default to their traditional age, especially when establishing social hierarchy.
Social hierarchy and language
Age is more than a number in East Asian cultures; it is the backbone of social interaction. In Korean and Japanese, grammar shifts based on the relative age of the speaker and listener. You must use specific honorifics and polite speech patterns when addressing someone older, even by a single year.
The traditional age system simplified this by grouping everyone born in the same year into the same age bracket. This created clear peer groups (chingu) and distinct senior-junior relationships. Knowing someone's age dictated everything from who pours the drinks to how you bow. The shift to international age has added a layer of complexity, as people must now calculate which age their interlocutor considers official.
Regional variations
While South Korea is the most cited example, the practice was widespread across East Asia. In China, the traditional system is known as Sui, where age increases on the Lunar New Year. Japan also used a similar counting method, known as Kazoedoshi, which has largely fallen out of daily use in favor of the international standard. Vietnam follows a similar lunar-based reckoning. These systems reflect a shared cultural heritage where time is viewed as a continuous, cyclical flow rather than a linear series of individual milestones.