Lunar Age Calculator (traditional East Asian age 虛歲, Korean & international age)

Understanding the lunar age calculator — concept and principle

This calculator gives a person's traditional East Asian lunar age (虛歲), together with the international age (만 나이), the Korean counting age and the year age, for any date. It helps with traditional customs, fortune-telling, older documents and explaining the differences between age systems.

How it is calculated

• Lunar year of birth = birth year, or the year before if born before that year's Lunar New Year.
• Lunar year on the reference date = calendar year, or the year before if Lunar New Year has not yet passed.
• Lunar age = lunar year now − lunar year of birth + 1.
• International age = completed years since the birthday.
• Korean counting age = calendar year now − birth year + 1 (changes on 1 January).
• Year age = calendar year now − birth year.

The principle

In the traditional reckoning, a baby is 1 at birth, counting the time in the womb roughly as a year, and everyone gains a year together at the Lunar New Year rather than on their own birthday. A person born just before Lunar New Year belongs to the old lunar year, and becomes 2 a few days or weeks later. The Korean counting age follows the same idea but uses 1 January. International age counts completed years from the birth date, and has been the official age in Korea since June 2023. The lunar age can therefore be up to two years higher than the international age.

Worked example

Default inputs: born 20 Jan 1990 (before that year's Lunar New Year), reference date 10 Nov 2026 (after Lunar New Year).

1. Lunar year of birth = 1990 − 1 = 1989.
2. Lunar year now = 2026; lunar age = 2026 − 1989 + 1 = 38.
3. International age: 10 Nov is after 20 Jan, so 2026 − 1990 = 36.
4. Korean counting age = 2026 − 1990 + 1 = 37; year age = 2026 − 1990 = 36.

How to read the result

For official purposes in Korea, use the international age (만 나이). Some laws, such as those on military service or youth protection, use the year age. Lunar age is mainly used in traditional contexts, such as zodiac signs and ancestral rites, and in some other East Asian communities.

Common mistakes

• Forgetting to mark a January or February birth before Lunar New Year.
• Assuming Lunar New Year falls on the same date every year.
• Mixing up counting age (1 January) and lunar age (Lunar New Year).
• Using lunar age on official forms.

Frequently asked questions

What is lunar age?

A traditional East Asian age that starts at 1 at birth and adds a year at each Lunar New Year.

Which age is official in Korea?

International age (만 나이), used as the standard since June 2023.

Why is my lunar age two years more than my real age?

You start at 1, and you gain a year at Lunar New Year before your birthday comes round.

Sources: Republic of Korea Ministry of Government Legislation, international age standardisation (Civil Act and Administrative Basic Act amendments, effective 28 June 2023)