How the target date is calculated
International age adds a year on each birthday, so the date you turn a given age is always your birth month and day, just in a later year — this reverses that: the target date is your birthday in (birth year + target age).
- birth year — the year from your date of birth
- target age — the international (만 나이) age you're counting to
More detail
Why the month and day never change
Because international age only advances on the birthday itself, the date you turn any given age always falls on your birth month and day — only the year shifts, by exactly the target age minus your current age in years.
Feb 29 birthdays
If you were born on Feb 29 and the target year isn't a leap year, that date doesn't exist, so this calculator rolls the result forward to Mar 1. The convention isn't settled: Korean Civil Act §160(3) ends a period with no matching day on the last day of that month, and common date libraries clamp the same way — both landing on Feb 28. Check which one your use case needs.
Tip. Useful for legal milestones tied to international age — like the age adults gain certain rights in Korea — since June 2023 those are counted by 만 나이, not the calendar-year 연 나이.
Frequently asked questions
What date will I turn 30 (or any target age)?
Enter your date of birth and 30 as the target age — the target date is your birth month and day in (birth year + 30), since international (만 나이) age only advances on the birthday itself.
Does this use 만 나이 or 세는 나이?
International age (만 나이), the legal standard in Korea since June 2023. It's birthday-based, unlike 세는 나이 (which adds a year every New Year) or 연 나이 (calendar year minus birth year).
What happens if I was born on Feb 29?
If the target year isn't a leap year, the calculated date rolls forward to Mar 1. Other conventions clamp to Feb 28 instead (Korean Civil Act §160(3) and most date libraries), so check the standard that applies to your case.
How is the D-day countdown calculated?
The D-day output is the target date minus today, shown as D-<n> if it's still ahead, D+<n> if it has passed, or D-DAY if today is the date.