Korean Age Calculator

Background.

A baby born in Seoul on 31 December is, by the traditional Korean reckoning, two years old the next morning. Under that system, 세는 나이 or counting age, a newborn starts at one and everybody gains a year together on 1 January, whatever their birthday. It is still the number many Koreans give when asked how old they are, and it is why a Korean colleague can be one or two years older in conversation than on their passport.

Two other counts run alongside it. 연 나이, year age, is simply the current year minus the birth year; it also ticks over for everyone on New Year's Day but starts from zero. 만 나이, international age, is the one used almost everywhere else: zero at birth and one more on each birthday. Since 28 June 2023 it is what Korean law means by age unless a particular statute says otherwise, under amendments to the Civil Act and the General Act on Public Administration passed in December 2022.

Enter a date of birth and the date to measure on, and all three come back together, along with the gap between counting age and international age, whether the birthday has arrived yet that year, and a note on which count applies where. The measuring date is a field rather than your device's clock because every count can change overnight on 1 January. Set it to today for the live answer, or to a past date to ask how old someone was then.

The 2023 reform did not retire the year count. Alcohol and tobacco sales, conscription, school entry and some public-service examinations still go by birth year.

What is korean age calculator?

Korean age usually means the traditional counting age, but South Korea has three ways of stating age, and they can give three different numbers on the same day. Counting age (세는 나이, se-neun na-i) is the current year minus the birth year plus one. Year age (연 나이, yeon na-i) is the current year minus the birth year. International age (만 나이, man na-i) is the number of full years completed since the date of birth. Counting age is always exactly one more than year age. International age equals year age once this year's birthday has passed and is one less before it, so counting age leads international age by two from 1 January until the birthday and by one from the birthday to the end of December. For a child who has not reached a first birthday, Civil Act Article 158 allows the age to be given in months.

How to use this calculator.

1. 01Enter the date of birth as YYYY-MM-DD. Only the year affects counting age and year age; the month and day decide the international age.
2. 02Set "Measured on" to today's date, or to any date since the birth: 2023-06-28, for instance, shows someone's three ages on the day the unified-age law took effect.
3. 03Quote the counting age (세는 나이) when someone in Korea asks your age in conversation, and the international age (만 나이) on forms, contracts, medical records and visa paperwork.
4. 04Use the year age (연 나이) when checking the age rules for alcohol and tobacco, military service, school entry or the lower public-service examinations.
5. 05Look at "Birthday already this year?" to see why the gap between counting age and international age is 1 or 2.

The formula.

Write Y for the year of the measuring date and B for the birth year. Year age is Y − B and counting age is Y − B + 1. Neither looks at the month or the day, which is why both change for everyone at once on 1 January. International age starts from Y − B and subtracts 1 if the birthday has not yet come round in year Y. The birthday counts as arrived on the day itself, so the international age goes up on the birthday, not the day after. On the day of birth the counting age is 1 and the other two are 0.

Since counting age is year age plus one, and international age is either year age or one below it, their gap can only be 2 (before the birthday) or 1 (from the birthday on).

One birthday needs its own rule: 29 February. In a common year there is no such date, and Civil Act Article 160(3) provides that a period fixed in years which ends in a month with no matching day matures on the last day of that month. A leap-day baby therefore becomes a year older on 28 February in common years. Some other jurisdictions use 1 March instead, and a note says so beside the result for a 29 February birth date.

Counting age here advances on 1 January, the convention the Korean government's own explanation of the reform uses. The traditional shared birthday was Seollal, the lunar new year in late January or February; for the weeks between the two new years a lunar-based count would be a year lower, and that version is not calculated.

A worked example.

Frequently asked questions.

References& sources.

1. [1]Korea Legislation Research Institute, Statutes of the Republic of Korea — CIVIL ACT (민법), English translation, current through Act No. 19098 of 27 Dec. 2022. Article 158 (Calculation and Showing of Age): 'The age of a person shall be calculated based on his/her date of birth, incremented by one year on his/her birthday, and shown on a yearly basis: Provided, That for a person whose first birthday has yet to come, his/her age may be shown on a monthly basis.' Article 160(3), relied on here for the 29 February anniversary: 'In cases where a period has been fixed by the month or year, if there is no corresponding day in the last month, the last day of the month shall be the day of maturity.' Retrieved 2026-07-30. The Korean text is the authoritative version.
2. [2]Korea Legislation Research Institute, Statutes of the Republic of Korea — GENERAL ACT ON PUBLIC ADMINISTRATION (행정기본법), English translation. Article 7-2, added by Act No. 19148 of 27 Dec. 2022: 'Except as provided in other statutes or regulations, the age for administrative purposes shall be calculated by including the date of birth and expressed in terms of years; provided, if a child has not reached the age of 1, his or her age may be indicated by the number of months.' Retrieved 2026-07-30.
3. [3]Republic of Korea, Government Policy Briefing (대한민국 정책브리핑, korea.kr) — '나이'로 인한 혼란 사라진다…'만 나이 통일'로 달라지는 것들. The official explanation of the 28 June 2023 enforcement date and of all three counts: 만 나이 as current year − birth year, less one more for a person whose birthday has not yet come; 연 나이 as current year − birth year regardless of birthday; and the note that the Youth Protection Act and the Military Service Act keep the year count. Retrieved 2026-07-30; Korean language.
4. [4]The Korea Herald, 'Korea starts using int'l age system, but exceptions remain' (2023). Secondary source for the concrete scope of the surviving exceptions: alcohol and tobacco from 1 January of the year a person turns 19, conscription examinations by birth year, elementary-school entry from 1 March of the year after a child turns 6 in international age, and lower-grade public-service examination eligibility by birth year. Retrieved 2026-07-30.
5. [5]International Organization for Standardization, ISO 8601-1:2019 — Date and time: representations for information interchange, Part 1: Basic rules. The YYYY-MM-DD calendar-date form both inputs on this page use. The full text is a purchased standard and was not opened; only the calendar-date representation is relied on, and it is uncontroversial.