About Korean Age
Korea has traditionally used a different way of counting age than most of the world, and it can produce a number that is one or two years higher than the age you're used to. This calculator converts a birth date into the three age systems you'll actually encounter: the traditional counting age, the now-official international age, and a separate "year age" used in specific Korean laws.
The three formulas
- Korean age (se-nai, 세는나이): a baby is considered 1 year old at birth (accounting for time in the womb), and everyone — regardless of their birth date — turns a year older together on January 1st. The formula is current year − birth year + 1. It ignores the birthday entirely; only the calendar year matters.
- International age (man-nai, 만나이): the birthday-based age used in most of the world. You are 0 at birth and gain a year on each birthday. The formula is current year − birth year, minus 1 more if this year's birthday hasn't happened yet.
- Year age (yeon-nai, 연나이): simply current year − birth year, with no birthday adjustment and no +1. It's used in a handful of Korean statutes (such as military enlistment and some school-related cutoffs) where a single number per calendar year is more practical than tracking individual birthdays.
Why Korean age is higher
Because Korean age starts at 1 (not 0) and increments on a fixed calendar date rather than the birthday, it is usually 1 year higher than international age. If the current date falls before this year's birthday, the gap widens to 2 years, since international age hasn't yet incremented for the year while Korean age already has (it moved on January 1st). A baby born on December 31st is considered "2 years old" in Korean age the very next day, despite being only 1 day old internationally.
Which system applies today
On June 28, 2023, South Korea passed legislation standardizing on international age (man-nai) for essentially all legal, medical, and administrative purposes — contracts, insurance, most official paperwork, and everyday age references now use the birthday-based count. Traditional Korean age (se-nai) is still used casually in conversation and some cultural contexts, and year age (yeon-nai) remains the rule for a small set of specific laws where it was already written into statute, such as the minimum age for alcohol and tobacco purchase and school-year cutoffs.