Formula and age-system rules
Traditional Korean age starts at 1 and increases on January 1. Year age starts at 0 and increases on January 1. International age starts at 0 and increases on birthdays.
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Korean Age Calculator
Compare international age, traditional Korean age, and year age.
Last updated: June 22, 2026
Calculate Korean age
Compare international, traditional Korean, and year age.
Guide
How this calculator works
Official context
South Korea officially moved to the international age system on June 28, 2023, but traditional Korean age is still searched and used informally.
Example input and output
A person born on December 31 can be 1 by international age before their first birthday, 2 by traditional Korean age after January 1, and 1 by year age in the new calendar year.
Common mistakes
Do not use traditional Korean age for official South Korean legal or administrative contexts after the 2023 change. Also do not confuse year age with traditional Korean age.
Best use and limits
Use this calculator to compare age-counting systems in cultural, language-learning, or informal contexts. Use international age when official documentation requires it.
Calculation steps
Step-by-step calculation
Step 1
Input
Born 2000-12-31, reference 2001-01-01
Step 2
Rule
Traditional Korean age starts at 1 and increases on January 1. Year age starts at 0 and increases on January 1. International age starts at 0 and increases on birthdays.
Step 3
Calculation
International age: Starts at 0 and changes on the birthday. Traditional Korean age: Starts at 1 and changes on January 1. Year age: Starts at 0 and changes on January 1.
Step 4
Result
Traditional Korean age 2, year age 1. Traditional Korean age starts at 1 and increases on January 1.
Calculation assumptions
This calculator compares three age systems side by side so the result is not confused with current official South Korean age rules.
| Assumption | How this page handles it |
|---|---|
| International age | Starts at 0 and changes on the birthday. |
| Traditional Korean age | Starts at 1 and changes on January 1. |
| Year age | Starts at 0 and changes on January 1. |
Example inputs and outputs
| Input | Output | Why it matters |
|---|---|---|
| Born 2000-12-31, reference 2001-01-01 | Traditional Korean age 2, year age 1 | Traditional Korean age starts at 1 and increases on January 1. |
| Born 2000-06-01, reference 2026-06-22 | International age depends on birthday; year age is 26 | Different systems answer different cultural or administrative questions. |
| Reference date before birthday | International age may be one lower than year age | Birthday timing is the key distinction for international age. |
Edge cases
Cases worth checking carefully
New Year's Day
Traditional Korean age and year age both change on January 1, but they do not start from the same base.
Official South Korean use
South Korea moved to the international age system for most official purposes in 2023.
International age
International age starts at 0 and changes on the birthday, which is different from traditional Korean age.
When to use and when not to use this calculator
Use it when
Use this calculator to compare age-counting systems in cultural, language-learning, or informal contexts. Use international age when official documentation requires it.
Do not use it when
South Korea uses the international age system for most official purposes. Traditional Korean age is mainly cultural or informal context.
Frequently asked questions
Is Korean age still official in South Korea?+
For most official purposes, South Korea uses international age after the 2023 reform.
What is year age?+
Year age starts at 0 and increases on January 1, unlike traditional Korean age which starts at 1.
Why can Korean age be two years higher?+
A person can start at 1 at birth and gain another year on January 1 before their birthday.
What changed in 2023?+
South Korea moved toward international age for most official and administrative purposes.
Why is traditional Korean age still searched?+
It remains useful for cultural context, language learning, and older informal references.
Sources and updates
We use these sources to define the age-counting rule, official context, or life-stage assumptions used by this calculator.
Last updated: June 22, 2026
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