The Korean age system counts people as 1 year old at birth, and everyone ages one year on January 1st, regardless of their actual birthday.
In South Korea (and historically in other East Asian countries), age is calculated differently than in Western countries. When you are born, you are considered 1 year old.
Everyone in Korea ages together on January 1st, regardless of their actual birthday. This means that a baby born on December 31st would turn 2 years old the very next day!
Note: South Korea officially adopted the international age system on June 28, 2023 for legal and administrative purposes, but Korean age is still commonly used in everyday conversations.
Two numbers, two systems. The mechanics differ in two places, and once you know them the rest is mechanical.
Take two people born in the same year. Person A is born on 5 February 2024. Person B is born on 20 December 2024. On 1 January 2025, Person A's international age is still 0 (her birthday hasn't come round again) and so is Person B's. Both of their Korean ages are now 2, because the Korean system starts everyone at 1 at birth and bumps everyone up one more on New Year's Day.
By the same Korean age, the gap between the oldest and youngest in a Korean cohort can be 364 days. The system doesn't care about that. Knowing both numbers lets you answer different questions about the same person.
Until June 2023 several different age systems were in use in Korea at the same time. Traditional Korean age (the +1 at birth, +1 at New Year version), calendar age (the +1 at New Year version without the birth bump, used for things like school admissions and military), and international age (used for some legal matters). This led to real confusion. Hospitals could record a newborn at different ages depending on which form they were filling out. Bank contracts written under one system could be misread under another.
On 28 June 2023 the South Korean government's uniform age law came into effect. From that date contracts, government forms, and administrative records default to international age unless they explicitly say otherwise. The change was framed as removing legal ambiguity rather than telling people how to think about their own age.
What didn't change is everyday social usage. When Koreans introduce themselves, ask age order at a meal, or talk about school year groupings, the traditional Korean age is still the default reference. Calculators like this one are useful precisely because both numbers still matter and they answer different questions.
Legal contracts. Bank account opening. Driving licence. Voting eligibility. Medical records and prescriptions. Government forms. Insurance.
Introductions, especially with strangers older than you. Asking age order at a group meal or among new colleagues. School year groupings (a "92er" cohort means everyone born in 1992). Some traditional ceremonies and family events.
When in doubt, ask which one the other person means. Many Koreans will spell it out, e.g. "international age 28, Korean age 30".
Military conscription: South Korea conscripts men in the calendar year they turn 18 in international age. The Military Manpower Administration explicitly uses international age, so the 2023 law change had no practical impact on conscription.
Drinking age: the legal drinking age in Korea is 19 in international age, meaning you can drink in the calendar year you turn 19. Before 2023 some venues used Korean age (effectively 20+1) which created confusion at the door. The 2023 law removed that ambiguity.
Birthday celebrations: most Koreans celebrate their actual birthday, the international one. The Korean age bump on 1 January isn't usually celebrated as a personal milestone, though there's often a passing remark about everyone being a year older.
Seollal (Korean Lunar New Year): historically some families counted the age increment from Seollal rather than 1 January. This varied by region and family. It explains why a small number of older Koreans give slightly different answers depending on the time of year.
Korean age is a traditional age-counting system used in Korea where everyone is considered 1 year old at birth, and everyone gains one year on January 1st regardless of their actual birthday. This means you can be up to 2 years older in Korean age than your international age.
Korean age is calculated by taking the current year and subtracting your birth year, then adding 1. The formula is: (Current Year - Birth Year) + 1. This means a baby born on December 31st would be 2 years old the very next day (January 1st).
The Korean age system has historical roots in East Asian culture where time spent in the womb was considered the first year of life. Additionally, counting everyone's age from January 1st simplified age-based social hierarchies and group interactions in Korean society.
The main differences are: (1) Korean age starts at 1 at birth, while international age starts at 0. (2) Korean age increases on January 1st for everyone, while international age increases on your birthday. This can make Korean age 1-2 years higher than international age.
As of June 28, 2023, South Korea officially adopted the international age system for legal and administrative purposes. However, Korean age is still commonly used in everyday conversations, social settings, and cultural contexts. Many Koreans use both systems depending on the situation.
Yes. The South Korean government passed a law in December 2022 that took effect on 28 June 2023, making international age the standard for legal and administrative purposes. Banks, contracts, and government forms now use international age by default. Korean age is still used informally in conversation, and 'manna' or 'man-nai' (the international system) is now what most documents care about.
Yes, a few. Cultural context (when meeting someone, age order still shapes social register), entry to bars and clubs in some venues, school year groupings, and certain types of military or medical referencing. In casual conversation it's still common to ask someone's Korean age, especially among older Koreans.
Because the system stacks two adjustments. You start at 1 the day you are born, not 0. Then every Korean New Year (January 1st) you gain another year, regardless of when your actual birthday falls. So a baby born on 31 December would be 1 at birth and 2 the next day, even though they have been alive less than 48 hours.