International Age & D-day Calculator
Enter a birth date to see your international age (만 나이) on a chosen date, or enter a target date to see how many days are left (D-day).
Show how it is calculated
International age: Subtract the birth year from the year of the reference date. Then subtract 1 more if the reference date is before that year's birthday. For someone born on October 14, 1990, on October 13, 2026 the subtraction gives 2026 − 1990 = 36, but it is one day before the birthday, so you subtract 1 and the age is 35. From the next day, October 14, the person is 36.
D-day: Subtract the reference date from the target date to count the days. If the reference date is October 13, 2026 and the target is December 25 of the same year, the difference is 73 days, so it is D-73. The target day itself is shown as D-Day, and days after it as D+1, D+2 and so on.
How to use
The upper box is for international age and the lower box is for D-day. In both boxes the reference date is filled in with today's date at first, so you only need to pick a birth date or a target date.
If you change the reference date, you can calculate for another day, such as "how old was I on that day?" or "how many days were left until the exam on that day?". This is useful for checking your age on a specific date such as an insurance start date, a contract date or a hire date. On a phone, tap a date field to open the calendar.
What is Korea's international age rule (만 나이 통일법)?
On June 28, 2023, the amendments to the Framework Act on Administrative Regulations (행정기본법) and the Civil Act (민법), often called the "international age unification law" (만 나이 통일법), took effect. According to a press release from the Ministry of Government Legislation (법제처), unless a special rule says otherwise, age in administrative and civil matters is calculated and stated as international age. This means that when only a number is written for age in a law, contract or official document, with no "만" in front, it is still read as international age.
Article 158 of the Civil Act states that "age is calculated in full years (만 나이), counting the day of birth, and is expressed in years," and adds that before the age of 1 it may be expressed in months. Saying a baby is "8 months old" fits this provision.
Korean age, year-based age and international age
Three ways of counting age were mixed in daily life in Korea. Take someone born on October 14, 1990 and count on October 13, 2026 to see the difference.
| Method | How it is counted | Example result |
|---|---|---|
| International age (만 나이) | 0 on the day you are born, plus 1 at each birthday | 35 (one day before the birthday) |
| Year-based age (연 나이) | This year − birth year | 36 |
| Korean age (세는 나이) | 1 at birth, plus 1 every New Year | 37 |
Year-based age is used to group everyone born in the same year, regardless of birthday. For that reason some laws still use it even after the international age law. According to a 2023 guide from the Korea Policy Briefing (정책브리핑), the age for buying alcohol and tobacco under the Youth Protection Act (청소년 보호법), the group subject to military service examinations under the Military Service Act (병역법), and the timing of entering elementary school under the Elementary and Secondary Education Act (초·중등교육법) do not use international age and follow separate standards. For example, the Youth Protection Act treats a person as a minor if "current year − birth year" is under 19.
On the other hand, systems that always used international age stay the same, such as the voting age (18), receiving the National Pension old-age pension, the retirement age (60 or older) and senior transport fare discounts (65 or older).
If you were born on February 29
People born on February 29, which exists only in leap years, have no birthday date in common years. This calculator follows Article 160, paragraph 3 of the Civil Act. It says that "when a period is set in months or years and the last month has no matching day, the period ends on the last day of that month."
So in a common year, the year is complete at the end of February 28, and you count one year older from March 1. For someone born on February 29, 2000, the result is 24 on February 28, 2025 and 25 on March 1, 2025. In a leap year, the age goes up on February 29 itself.
How D-day is shown
D-day counts the days remaining until a target date. This calculator shows D-number when there are days left, D-Day on the target day itself, and D+number when the date has already passed. If today is October 13 and the exam is on October 16, it is D-3, and an event that ended two days ago is D+2.
The days are only the difference between the two calendar dates. Hours and minutes are not counted, so the result is the same whether you calculate at 11 p.m. or 7 a.m. on the same day.
Basis of the calculation
- Ministry of Government Legislation (법제처) press release "From now on, international age is your age" (2023-06-26) — effective June 28, 2023, checked 2026-10-13
- Korea Law Information Center (국가법령정보센터), Civil Act Article 158 (calculation and expression of age) and Article 160 (calculation by calendar) — checked 2026-10-13
- Korea Policy Briefing (대한민국 정책브리핑) "What changes and what does not change with the international age law" (2023-06-22) — checked 2026-10-13
The Ministry of Government Legislation has been reviewing individual laws that use year-based age with a view to aligning them with international age. If you want to know the age standard of a specific system, such as school entry, military service or buying alcohol, also check the relevant law or the guidance of the responsible agency.
Common mistakes and things to watch for
- Reading an age as Korean age because "만" is missing: Since the law took effect, ages in laws and contracts are treated as international age even without "만".
- Assuming every system uses international age: There are exceptions that use year-based age or a separate standard, such as buying alcohol and tobacco, military service and entering elementary school.
- Counting anniversaries as D-day: The "day number" style that counts the day you started dating or the day a baby was born as day 1 differs from D-day by one day. In this calculator, D+1 means the day after the target date.
Frequently asked questions
Exactly when does international age go up by one?
You become one year older on your birthday itself. Until the day before your birthday, your age stays the same as before.
Can I buy alcohol and tobacco from age 19 (international age)?
The Youth Protection Act (청소년 보호법) decides who is a minor by "current year − birth year", not by international age. So everyone born in the same year can buy them together from January 1 of that year, regardless of birthday.
When does someone born on February 29 get older in a common year?
Under Article 160, paragraph 3 of the Civil Act, the year is complete only after the last day of February, the 28th, has passed. In a common year, this calculator shows one year older from March 1.
Is the target day D-0 or D-Day?
Both mean the same thing, but this calculator shows D-Day. From the next day on, it shows D+1.
Calculators that go well with this one
- Severance Pay Calculator — see your length of service and severance pay from hire and leave dates
- Deposit & Savings Interest Calculator — preview how much you will have by the maturity date