8 Interesting Facts About How Age Is Calculated Worldwide
“How old are you” sounds like a simple question, but the answer has depended on where you’re standing for most of human history. Here are 8 facts about how age has been (and still is) calculated around the world.
1. The international system counts from zero
The system used by most of the world today counts age from zero at birth, adding a year on each birthday. This is the method our own age calculator uses, the same method used to work out the exact age gap between two people.
2. South Korea legally abolished “Korean age” in 2023
Under the traditional East Asian system, a baby was considered 1 year old at birth, with everyone gaining a year on January 1st regardless of their actual birthday. South Korea’s parliament passed a law standardizing on the international age system, which took effect in June 2023, though the term “Korean age” is still used informally in social contexts.
3. Japan dropped the traditional system decades earlier
Japan officially moved away from the traditional East Asian age-counting method back in 1950, making South Korea the last country in the region to use it for legal purposes.
4. A December-born baby could “turn 2” the next day
Under the old Korean age system, a baby born on December 31st would already be considered 1 year old at birth, and then turn 2 on January 1st, the very next day.
5. Some countries still use a separate legal age system
Even after 2023, South Korea kept a separate “counting age” method (age from zero, plus a year every January 1st) specifically for things like the legal drinking age and school entry requirements.
6. Leap year birthdays create their own quirks
People born on February 29th technically have a birthday only once every four years, and different countries and institutions have different legal conventions for which date counts as their birthday in non-leap years.
7. Some cultures count age using the lunar calendar
Certain traditional calculations tie age to the lunar calendar rather than the solar (Gregorian) calendar most of the world uses, which can shift the calculated age by weeks depending on the year.
8. “Age as of” a specific date matters legally everywhere
Regardless of the counting system, most legal contexts, voting eligibility, retirement benefits, contract law, calculate age as of a specific reference date, not just “today,” which is why an accurate age calculation matters beyond simple curiosity.
Whichever date you need to calculate from, our age calculator handles the international system accurately, including leap years.
Does South Korea still use the old age-counting system?
No, not officially. South Korea’s government standardized on the international age system starting in June 2023, though “Korean age” is still used informally in everyday conversation.
Why did some countries historically count age differently?
The traditional East Asian method counted the time spent in the womb as the first year of life, reflecting a different cultural view of when life begins being counted.
What age system does this calculator use?
Our age calculator uses the international system, counting from zero at birth and adding a year on each birthday, the method used by most of the world today.
Written by EquateWorld Team
Part of the EquateWorld editorial team.
