BirthdayAsk someone in Seoul in 2022 how old they were, and the answer could easily be two years higher than the age on their passport. Age feels like a simple fact, but the way it is counted is a convention, and different countries and traditions have used different ones. Understanding the difference saves you from wrong answers on forms, applications and even everyday conversations.
International age: the system most of the world uses
International age is the number of full years you have completed since the day you were born. You are 0 at birth and you become a year older only on your birthday. This is the age printed in passports, used on most visa and immigration forms, and recorded in medical files in the vast majority of countries. Our Age Calculator uses exactly this method.
Traditional East Asian age counting
In traditional Korean age counting, a baby is already 1 year old at birth, and everyone gains a year on January 1st rather than on their birthday. That means a baby born on December 31st turns 2 the very next day. Depending on when your birthday falls, traditional age is one or two years higher than international age. Similar reckoning has long existed in China, where it is called xusui, and in Vietnam, although international age is now the standard in official use in those countries.
What changed in South Korea
For many years South Korea used several systems at once: the traditional count in daily life, a year-based count (current year minus birth year) for certain laws, and international age for medical and some legal purposes. In June 2023, new rules made international age the standard for most legal and administrative purposes. A few laws, such as some of those on alcohol, tobacco and military service, still count by birth year, so you may still meet more than one number in practice.
Why this matters when you fill in a form
Most mistakes do not come from the counting system but from the reference date. A form may ask for your age today, your age on a specific cut-off date such as the first day of a school year, or your age on December 31st. These can all give different answers for the same person. Always read which date the form uses, then calculate your age as of that exact date. In our Age Calculator, use the 'Calculate age as of' field to do exactly that.
A quick conversion rule
To convert from international age to traditional Korean age, add one year if your birthday has already passed this year, or two years if it has not yet happened. To get the year-based age, simply subtract your birth year from the current year. For example, someone born on June 15, 2000 is 26 in international age in October 2026, 27 in traditional age, and 26 by the year-based count. Someone born on December 20, 2000 is 25 internationally, 27 traditionally, and 26 by the year-based count.
When you are not sure which number a form wants, ask, or default to international age, which is what most official documents outside East Asia expect. And if you need to compare two dates, such as the age gap between two people, our Date Difference Calculator gives you the exact result in years, months and days.