How age is calculated
Your age is the number of birthdays you have had: you are 0 on the day you are born and gain one year on each birthday. The exact age adds the months and days since your last birthday — for example, someone born on 25 October 2000 is 25 years, 11 months and 24 days old on 19 October 2026, and turns 26 six days later.
Months are counted by calendar date. If a month has no matching day (say you were born on the 31st), the last day of that month is used.
What is "Korean age"?
Traditionally, Koreans counted age differently: a baby was 1 year old at birth and everyone got one year older on 1 January. So the traditional "Korean age" is the current year minus the birth year, plus one — often one or two years more than your actual age.
Since 28 June 2023, South Korean law uses the international age (만 나이) for laws, contracts and official documents unless a specific law says otherwise. You will still hear the counting age in everyday conversation, and a few laws use the "year age" (current year minus birth year). 한국어 계산기
Source: Korea Ministry of Government Legislation (law.go.kr) — Civil Act Article 158, Framework Act on Administration Article 7-2.
Age systems in East Asia
| System | At birth | Gets older on | Used today |
|---|---|---|---|
| International age | 0 | Each birthday | Worldwide; official in Korea, Japan and China |
| Korean counting age | 1 | 1 January | Everyday speech in Korea |
| Chinese nominal age (虚岁) | 1 | Chinese New Year | Traditional customs in China |
| Japanese kazoedoshi (数え年) | 1 | 1 January | Some traditional events in Japan |
Frequently asked questions
How old is someone born on 29 February in a non-leap year?
There is no 29 February in a common year, so the extra year is counted either on 28 February or on 1 March. Rules differ between countries and even between states, so this calculator lets you choose. The default (1 March) matches how age periods are counted in Korea and Japan.
Is my date of birth stored anywhere?
No. Everything is calculated in your browser and nothing is sent to our server.
Why does the Chinese zodiac sometimes differ from my birth year?
The zodiac year starts at Chinese New Year, which falls between late January and mid-February. If you were born before it, your zodiac sign belongs to the previous year. This calculator uses the Chinese calendar built into your browser to find it.
Related tools
- Date Calculator — days between dates, add or subtract days