Korean age explained: international, counting and year age

1. What the three ages are

The international age starts at zero on the day you are born and adds one on each birthday. Before the first birthday it can be written in months. The counting age, the traditional Korean age, starts at one at birth and everyone adds one together on 1 January. The year age is the current year minus the birth year, so everyone born in the same year shares it regardless of birthday.

The Civil Act and the Framework Act on Administration were amended on 27 December 2022 and took effect on 28 June 2023. Since then an age in a law, a contract or an official document is read as the international age even without the word for it. The Ministry of Government Legislation calls this the unification of age, and its page carries a calculator and a list of questions. This app's formula was checked against that calculator on 24 cases.

The unification did not rewrite every law. The Youth Protection Act and the Military Service Act define, inside their own text, a count that adds a year when the calendar year changes, and primary school entry falls on 1 March of the year after a child turns six, which makes the birth year the deciding fact. The ministry counted about sixty such laws and said they would be revised one by one.

2. The basic rules

There are two formulas for the international age. If this year's birthday has not come, subtract the birth year from the current year and then subtract one more. From the birthday onward, subtract the birth year only. The ministry's guidance says the new age begins at midnight on the birthday. The counting age is the year age plus one, so to know all three you only need to know whether the birthday has passed.

Copying the ministry's own example, a person born on 8 July 1992 was 30 by international age, 32 by counting age and 31 by year age on 1 January 2023. After the unification that person is simply 30.

Before the first birthday an age may be written in months, which is why vaccination schedules and childcare forms ask in months. This app shows the month count whenever the international age is zero.

3. The rules inside this app

This app first counts the months since birth. Multiply the year difference by twelve, add the month difference, and subtract one if the day of the reference date is smaller than the day of the birth date. The international age is that month count divided by twelve, rounded down. The year age is the year difference, and the counting age is the year age plus one.

Someone born on 29 February keeps the previous age through 28 February of a common year and goes up on 1 March. A baby born on 31 January is still zero months on 28 February and one month on 1 March. Neither rule was invented here; they are what the ministry's calculator answered, followed as is. So the next age-up date shown for a 29 February birthday in a common year is 1 March.

The reference date is today when left empty, and whatever date a form names otherwise. A start date or a filing deadline written in a notice is the reference date. If the reference date is before the birth date, nothing is calculated and the screen says so.

The right column of the law table re-reads your age with the ruler each clause uses. Laws that use the international age get that number, laws that add a year with the calendar get the year age, and the school entry row gets 1 March of the birth year plus seven. The clauses were fetched through the national law database's public API and copied without changing a character, with the check date and the in-force date shown in the table.

The dates you enter do not go to a server. The calculation finishes inside the browser, and the server learns only three facts: that the page was opened, that a calculation appeared once, and that the link was copied. Nothing is saved, so a refresh clears it. There is no zodiac reading.

4. Getting it right on a form

When writing an age on a form, first find the reference date that form sets. Job notices usually use the filing deadline or the planned start date, and exams use the exam date or the filing date. Put that date in the reference box and write the international age, and you will be right most of the time. Ages in laws and notices are international ages even without the word.

Age conditions in contracts work the same way. Things that were already set by international age, such as the national pension starting age, the basic pension and civil servant retirement, did not change with the unification. Resident registration cards and driving licences remain valid as they are.

When explaining to someone outside Korea, the international age is the same age they already use. The counting age is a custom, and the year age is a count that a few laws use. The Korean version of this page shows the same table.

5. A little deeper

The Youth Protection Act defines a youth as a person under 19, but excludes anyone who has reached 1 January of the year they turn 19. So even a December birthday stops being a youth from 1 January of that year. The rule treats everyone born in the same year alike regardless of birthday, and the limits on alcohol, tobacco and entry to certain venues follow this definition.

The Military Service Act, when it states the timing of service duty as an age, says that from a given age means from 1 January of the year that age is reached, and up to a given age means until 31 December of that year. Ages in a draft physical or enlistment notice are read with this rule.

Primary school entry is 1 March of the year after the year in which the child turns six. That works out to 1 March of the birth year plus seven, and a January child and a December child of the same year enter on the same day. The exceptions allowing entry a year earlier or later are in paragraph 2 of the same article.

Milestone birthdays such as the seventieth and eightieth are custom rather than law, and many families keep them by the counting age. The ministry wrote that private customs are not something to force. The sixtieth, hwangap, is by international age.

6. Where people get stuck

On the birthday itself the age has already gone up. The line asking whether this year's birthday has passed counts the day itself as passed.

A person born on 31 December becomes two by counting age the very next day, while still zero months by international age. It is the day the three differ most, and the calculation is not wrong.

A 29 February birthday calculated on 28 February of a common year still shows last year's age. Try again on 1 March and it goes up. Some calculators move it up on 28 February; this app follows the ministry's calculator.

With the reference box empty, the calculation uses today. If yesterday's result differs from today's, a birthday fell in between.