Age, Zodiac & Star Sign
Age, star sign, zodiac, birthstone, flower & color at once.
Left blank, today's date is used.
Lunar birthdays are converted to solar to compute age & sign (1900–2100).
Age (international)
0yrs
One birth date gives you age, counting age, zodiac and star sign at once.
What is "Korean age" (man-nai)?
Since June 28, 2023, Korea's laws, contracts, and official documents use the international age system (man-nai) by default: age starts at 0 at birth and increases by one on each birthday. This replaced the mixed use of "counting age" (1 at birth, +1 every Jan 1) and "year age" (current year minus birth year).
How it is calculated
Age = reference year − birth year − (1 if the birthday hasn't occurred yet this year, else 0)
For example, someone born on Aug 20, 1995, evaluated on Jul 8, 2026 (before the birthday) is 2026 − 1995 − 1 = 30. Evaluated on Sep 1, 2026 (after the birthday), the age becomes 31.
Age systems compared
| Type | Formula | Increment |
|---|---|---|
| Counting age | Starts at 1 at birth | Every Jan 1 |
| Year age | Reference year − birth year | Every Jan 1 |
| Korean age | Reference year − birth year (−1 before birthday) | Every birthday |
How are zodiac & star sign decided?
The Chinese zodiac comes from the birth year via (year − 4) mod 12 (Rat, Ox, Tiger … Pig). The star sign comes from the birth month and day. Enter one birth date and you get age, counting age, zodiac and star sign together.
Where Korean age reckonings diverge
Since the age-reckoning unification act took effect on 28 June 2023, administrative and contractual age in Korea means international age. Everyday speech and a few statutes still use other reckonings, so one person's age can differ between documents.
How the three ages are counted
International age starts at zero on the day of birth and adds a year at each birthday. Where a Korean statute now says simply 'age', it means this.
Calendar-year age subtracts the birth year from the current year, ignoring the birthday. Its simplicity suits schemes that must divide people by year in one pass.
Traditional Korean age begins at one at birth and adds a year each New Year. It carries no legal force but persists in conversation, and a December birth can reach two within a month — a gap of up to two years against international age.
Where calendar-year age survives
Some areas still run on calendar-year age. Military examination and conscription cohorts are grouped by birth year, so notices arrive in the same year regardless of birthday.
The Youth Protection Act also uses calendar-year age, which is why alcohol and tobacco restrictions turn on the year rather than the birthday, and school entry age is set the same way.
It is worth checking which reckoning a form means, especially where eligibility carries an upper or lower age limit — the qualifying group changes with the choice.
Leap-day births
A 29 February birth has no birthday in common years. Age is generally treated as advancing once 28 February passes, and civil-law period calculations use the last day of the month.
International age advances on the birthday itself, and the hour of birth is not considered.
Legal basis
- International age as default — Framework Act on Administration art. 7-2, Civil Act art. 158
- Calendar-year age — Military Service Act, Youth Protection Act, Elementary and Secondary Education Act
- Unification act in force — 28 June 2023