Age Calculator

About Age Calculator

Enter a date of birth and a reference date, and this calculator gives your age in completed years, months and days. Next to it are two Korean age systems, “year age” and “counting age,” plus days until your next birthday, the age you'll turn then, total days alive, your Chinese zodiac animal and your Western star sign.

For most readers only the first number matters: it's the age used on passports, contracts and nearly every legal form worldwide. The other two columns exist because South Korea ran three age systems side by side for decades and still uses two of them in law. If you've ever been told a Korean friend was “two years older in Korea,” this table shows exactly why.

How the tool counts completed years, months and days

The years figure goes up on your birthday, never before. The months and days are counted on the calendar: the tool finds the most recent “month-birthday” (the same day-of-month as your birth, or the last day of a shorter month) and counts the days since. When a month is too short to contain your birth day, the month completes on its last day: a baby born on January 31 is 0 months 27 days on February 27, 1 month 0 days on February 28, 1 month 1 day on March 1, and 3 months 0 days on April 30.

Change the reference date to calculate age at a past or future moment: how old you'll be on a visa application date, or how old a grandparent was on their wedding day. The total-days figure is simply the number of calendar days between the two dates.

Korea's three ages, and the 2023 switch

Korean counting age (se-neun nai) starts at 1 at birth and adds a year every January 1. Year age (yeon nai) is the current year minus the birth year. International age (man nai) is the one everyone else uses.

On June 28, 2023, amendments to Korea's Civil Act (Article 158) and the Framework Act on Administrative Affairs took effect, stating that age is counted from the date of birth in completed years, with months allowed for infants under one. Since then, any age written in a law, contract or official document is read as international age unless that law says otherwise.

Some laws do say otherwise. The Military Service Act treats “from age X” as from January 1 of the year you turn X, so everyone born in the same year becomes eligible for conscription screening together. The Juvenile Protection Act defines minors as under 19 but excludes anyone who has reached January 1 of the year they turn 19, which is why a Korean born in December 2007 could legally buy alcohol from January 1, 2026. That is the “year age” column. Counting age no longer has legal force anywhere; it survives in conversation.

The gap between the three numbers

After your birthday in a given year, international age equals year age and counting age is one higher. Before your birthday, international age is one lower than year age and two lower than counting age. The extreme case is a baby born on December 31: the next day it is 1 day old, 1 in year age and 2 in counting age.

Leap-day birthdays: tool convention vs. the law

In years without February 29, this page treats February 28 as the birthday by default: the age ticks over that day and the countdown targets it. That is a common software convention, not a universal legal rule, and jurisdictions answer the question differently. When you enter February 29 as the birth date, a selector appears so you can switch to March 1 instead.

Under Korea's Civil Act, age is a period that starts on the day of birth; a period in years ends on the day before the corresponding date, and if that date doesn't exist in the final month, on the last day of that month. For a February 29 birth in a common year, the year ends at the close of February 28, so the new age legally starts on March 1, which is what the March 1 option applies. Japan's Act on Calculation of Age applies the same Civil Code rule (Article 143), which Japanese law phrases as reaching the new age on February 28 and being older from the following moment. If a deadline hinges on that single day, check the rule that actually governs it.

Zodiac results are approximations

The zodiac animal is assigned by Gregorian birth year only. Traditionally the animal changes at Lunar New Year (or at the start of spring, around February 4), so anyone born in January or early February may belong to the previous year's animal. Star-sign boundaries also shift by a day from year to year, while the tool uses a fixed table.

Worked examples

How to use it

1. Enter the date of birth.
2. Leave the reference date as today, or set it to the date you care about (an application deadline, a school start date).
3. Read the international age first; use the Korean columns only if you're dealing with Korean law or culture.

Frequently asked questions