Ask “how old are you?” in different places and the same person can give different answers, not because they’re fibbing, but because age has been counted in different ways. Here are the main systems and where they’re still used.
International age: the most common system
Almost everywhere, and in almost every legal system, age is counted in completed years: you’re 0 at birth and a year older on each birthday. It’s sometimes called “international age” or, in East Asia, “full age” or “man age”. All of our calculators use it.
Traditional Korean age
Under the traditional Korean system, a baby is 1 at birth, and everyone gets a year older on 1 January, not on their birthday. The formula is simple:
Korean age = current year − birth year + 1
That leads to some striking results. A baby born on 31 December was 1 at birth and turned 2 the very next day, on 1 January, while by international age they would still be 0 for almost a year. Depending on when your birthday falls, Korean age is one or two years higher than international age.
Korea also used a third count, “year age”: the current year minus the birth year, so you’re 0 in the year you’re born and everyone born in the same year changes age together on 1 January.
South Korea’s 2023 switch
On 28 June 2023, amendments to South Korea’s Civil Act and Framework Act on Public Administration took effect, making international age the standard for legal and administrative purposes. Overnight, most people became one or two years younger on paper.
The change didn’t reach every law. Several statutes kept counting age by calendar year, notably:
- Alcohol and tobacco: under the Youth Protection Act, young people can buy them from 1 January of the year they turn 19.
- Military service: the Military Service Act uses the calendar-year age to decide when men are called up.
News reports at the time also listed school entry, which goes by birth year, and eligibility for some civil service exams among the exceptions.
In everyday life, traditional Korean age is still widely understood, and you’ll often hear it in conversation.
China: xusui
China’s traditional “nominal age”, xusui (虚岁), works much like Korean age: you’re 1 at birth and a year older at the Lunar New Year (Spring Festival) rather than on 1 January. It’s still used in some families and for traditional occasions. Official documents and everyday modern use count completed years, called zhousui (周岁).
Japan: kazoedoshi and the age laws
Japan’s traditional count, kazoedoshi (数え年), also starts at 1 and adds a year at New Year. Japan moved legal age counting to completed years with the Act on Calculation of Ages in 1902, and a 1949 law encouraged people to use completed years in everyday life too, from 1950. Kazoedoshi survives in some traditions, such as the “unlucky years” (yakudoshi) observed at shrines and temples.
Japanese law has one more quirk: a person is treated as reaching a new age at the end of the day before their birthday. That’s why children born on 1 April start school a year ahead of those born on 2 April: by the start of the school year on 1 April, they have already reached the qualifying age.
Vietnam and other traditions
In Vietnam, the traditional tuổi mụ (nominal age) similarly adds a year at birth and increases at Tết, the Lunar New Year, while official documents use completed years. Variants of East Asian age reckoning existed across the region, and you may meet them in family records, horoscopes and traditional ceremonies.
Converting between systems
If you know a traditional East Asian age and want the international one (or the reverse), these rules cover most cases:
- International → Korean: add 2 if you haven’t had your birthday yet this year, or 1 if you have.
- Korean → international: subtract 1 if you’ve had your birthday this year, or 2 if you haven’t.
- Korean age → birth year: current year − Korean age + 1.
For Chinese and Vietnamese nominal ages, the year changes at Lunar New Year rather than 1 January, so early-year birthdays need a little more care; our zodiac sign calculator shows the exact Lunar New Year date for any year. To go from an international age back to a birth year, use What year was I born?, and for your exact age in completed years, the age calculator.
Frequently asked questions
What is my Korean age?
Under the traditional system, your Korean age is the current year minus your birth year, plus one. So everyone born in 2000 is 27 in Korean age throughout 2026, whatever their birthday. South Korea now uses international age for most official purposes.
Does South Korea still use Korean age?
Not officially. Since 28 June 2023, legal and administrative ages use international age. Some laws, such as those on buying alcohol and tobacco and on military service, still count by calendar year, and the traditional count survives in everyday conversation.
How do I convert Korean age to international age?
Subtract 1 if you’ve already had your birthday this year, or 2 if you haven’t.
Sources
- South Koreans grow younger overnight as the country changes how it counts people’s ages — Associated Press (via The Washington Times) (2023)
- Koreans Becoming Younger: Unification of Age-Counting Systems — In Custodia Legis, Law Library of Congress (2023)
- Act on Calculation of Ages (Act No. 50 of 1902) — Japanese Law Translation, Ministry of Justice, Japan
First published 29 October 2026. We review guides when sources change; see our editorial policy. Spotted an error? Tell us.