Korean Age vs. International Age: What's the Difference?

The Three Age Systems

Until recently, South Korea used three different systems for calculating age. Although the "International Age" system is now the legal standard, the traditional systems are still common in daily life.

1. International Age (Man-nai)

This is the system used by most of the world (and since June 2023, the official legal standard in Korea).

• Starts at: 0 years old.
• Increases: On your birthday.
• Formula: Current Year - Birth Year (subtract 1 if birthday hasn't passed).

2. Traditional Korean Age (Se-neun-nai)

This is the most common system in social settings.

• Starts at: 1 year old (you are 1 the moment you are born).
• Increases: On January 1st every year (everyone ages together).
• Formula: Current Year - Birth Year + 1.

3. Annual Age (Yeon-nai)

Used for certain laws like the Military Service Act and Juvenile Protection Act.

• Starts at: 0 years old.
• Increases: On January 1st.
• Formula: Current Year - Birth Year.

Why the Change?

Starting June 28, 2023, South Korea officially adopted the International Age system for all legal and administrative purposes to reduce confusion and legal disputes. However, asking "What year were you born?" remains a polite way to establish seniority in social contexts.