Age isn’t counted the same way everywhere
Most of the world uses what’s sometimes called “international age”: you’re 0 at birth, and you turn a year older on each birthday. It feels universal, but it’s one convention among several that have been used across East Asia.
Traditional Korean age reckoning (a version of a broader East Asian counting system with roots in China) works differently on two points at once. First, a baby is considered 1 year old at birth, not 0. Second, everyone’s age increases by one on New Year’s Day, not on their individual birthday. The practical effect is that someone born in December is 2 years old within days of being born under this system, having been 1 at birth and then gaining a year at the very next New Year.
This means traditional Korean age runs one to two years ahead of international age, depending on the time of year — the exact gap depends on whether this year’s birthday has passed yet.
South Korea’s 2023 change
The 2023 change did not take the traditional count out of the law, because by then it was not in the law. Korean law and official records had counted age the international way for decades — news reports of the change date that to the 1960s — and the ages on passports, for retirement benefits and for prosecution as a juvenile all ran on actual dates of birth. What the country had was three systems in use at once: traditional age in everyday speech, international age in most law, and a third, calendar-year age, used for a few legal thresholds such as conscription and the age at which alcohol and tobacco may be bought. That calendar-year count is simply the current year minus the birth year.
The change came in amendments to the Civil Act and the Framework Act on Public Administration, passed in December 2022 and in force from 28 June 2023. They made international age the default: an age in a law, a contract or an official document now means international age unless it says otherwise. The aim was to end the confusion of three counts, which had led to legal disputes and, during the pandemic, to muddles over who was eligible for a vaccine.
The calendar-year count was deliberately kept for school entry, conscription, the purchase of alcohol and tobacco, and civil service examinations, which are easier to run by year of birth than by each person’s birthday. Traditional counting continues socially — many Koreans still give their traditional age in casual conversation, particularly older people. The law and everyday speech still use different systems side by side.
Three systems, one birth date, as a worked example
Take someone born on 15 December 2000, and ask how old they were on 1 January 2001 — barely a fortnight later. Korea had three answers in use at once.
| System | Age on 1 January 2001 | How it counts |
|---|---|---|
| International age | 0 | No birthday has passed yet. |
| Traditional Korean age (세는 나이) | 2 | One at birth, and everyone gains a year at new year. |
| Calendar-year age (연 나이) | 1 | Simply the current year minus the birth year. |
Three numbers for the same child on the same day. The international age was the one on their legal documents then and is now; the calendar-year age is still the one that decides the year they start school and the year they may buy alcohol.
Japan’s history with the same system
Japan counted the same way, and the traditional reckoning has a name there: kazoedoshi, against man nenrei for the international count. Japan made the international count the legal one in 1902, and because people went on using the old count, a further law in 1950 encouraged everyone to use the international one in daily life, which is what happened. What survives is customary rather than administrative: yakudoshi, the years held to be unlucky, are counted in kazoedoshi, and Shichi-Go-San, the shrine visit at three, five and seven, is often reckoned by it too. Korea’s path was different: the traditional count stayed in everyday conversation until the 2023 change and, informally, after it.
Why this matters for a birthday reference
If you’re asking “how old is someone born on this date,” the answer depends on which age system you mean, and in South Korea, on which purpose you’re asking for. A tool that reports a single age figure is choosing international age, which is the right default for law almost everywhere, including South Korea — but not the number many Koreans would give if you asked them.
This sits alongside a broader theme on this site: a birth date can sort into more than one category depending on which counting or calendar convention is applied to it, the same way a birthday can land in a different Chinese zodiac year than the calendar year would suggest (see why a January birthday often gets the wrong Chinese animal), or fall into different generational cohorts depending on which researcher’s boundaries you use (see who decides where a generation starts and ends).