Korean Age Calculator

Historically, many Koreans used 세는나이 (Korean age): everyone is 1 at birth and gains a year on New Year’s Day (Gregorian January 1 in this simplified model). That made people one or two years “older” than international (만나이) age on paper.

In June 2023 South Korea began using international age — the same counting as most Western countries — for legal and official purposes. Birthdays increment age; there is no extra +1 at January 1. This calculator applies the traditional +1-at-birth, +1-each-New-Year folk formula so you can compare with older media or family customs.

Example: born July 1, 2000, referenced to August 7, 2026 — traditional Korean age is 27 (2000 counts as age 1, plus one year for each calendar year passed). International age on the same reference date is 26.

The gap between the two systems is usually one year, but it can be two. Someone born in December turns one at birth under traditional counting, then gains another year on January 1 a few weeks later, while international age stays zero until the first birthday — so for that short stretch the traditional figure is two years higher.

South Korea's June 2023 Civil Act amendment switched official documents, contracts, and most public services to international age (만나이). The folk formula (세는나이) remains in casual speech, media references, and older records, which is why both numbers still appear in conversation.

A third system, year age (연 나이), simply subtracts birth year from current year and ignores the birthday entirely. It was used for some military and school cutoffs and sits between the other two — this tool does not compute it, but knowing it exists explains why three different ages can circulate for the same person.

This simplified model increments at Gregorian January 1, not Lunar New Year. Some families historically counted the year change at Seollal instead, which shifts the +1 by a few weeks in January or February — ask which convention someone means if the number seems off.

For legal purposes after mid-2023, use international age only. Treat the traditional figure as cultural context for older media, family conversation, and comparing ages quoted before the reform.