Three ages
- International age (만 나이, man-nai): completed years since birth, as in most countries. You are 0 at birth and add a year on each birthday.
- Counting age (세는 나이): the traditional Korean age. You are 1 at birth and everyone adds a year on 1 January. It is the current year minus the birth year, plus one.
- Year age (연 나이): the current year minus the birth year, ignoring the birthday.
Someone born on 31 December 2000 is, on 5 October 2026, 25 in international age, 26 in year age and 27 in counting age.
The 2023 change
Since 28 June 2023, laws, contracts and official documents in Korea use international age unless a law says otherwise. Before that, people often used counting age in daily life, which made Koreans one or two years "older" than in other countries.
Where the others still apply
A few laws still count year age, notably military service and the youth protection rules that decide when you can buy alcohol and tobacco. In conversation, older people may still give their counting age.
The Korean Age Calculator gives all three for any date, and the Age Calculator gives an exact age in years, months and days.