Age Calculator

International age (also called Western age) counts completed years since birth and increments on the actual birthday. Korean age (seunnai or counting age) counts the year of birth as year 1 and adds 1 every January 1st regardless of the actual birthday. A person born on December 31 becomes 2 years old in Korean age the very next day on January 1st, even though they are only 1 day old in international age.

Days lived is calculated as the integer difference between today's date and the birth date, computed in milliseconds and divided by 86,400,000 (milliseconds per day), then floored to an integer. The birth day itself is counted as day 0, so a person born today has lived 0 full days. The count increases by 1 each midnight.

The Chinese zodiac cycle repeats every 12 years. This calculator assigns the zodiac animal using birth year modulo 12, mapped to the sequence: Monkey, Rooster, Dog, Pig, Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Goat. Note that the traditional Chinese New Year starts in late January or February, so if you were born in January or early February, your zodiac year may correspond to the prior calendar year.

Korean age (세는나이) has been used in Korean culture for centuries and is rooted in the concept that a child is considered to have lived through one year of existence during the pregnancy period. The system simplifies social calculation because everyone in the same birth year shares the same Korean age for most of the calendar year. As of 2023, South Korea officially adopted international age for legal and administrative purposes, though Korean age remains common in everyday speech.

The tool uses your local browser time and computes dates using JavaScript's Date object normalized to local midnight. This means the countdown reflects when midnight occurs in your local time zone, which is the natural expectation for most users. If you need UTC-based calculation, the tool's client-side nature means you can use any browser in your preferred time zone setting.

If you enter a date in the future, the international age calculation will return a negative number of years and the days lived will be a negative count. This is technically correct mathematically (days until birth) but the tool does not apply special handling — it is designed for past birth dates. Enter a valid past date of birth for meaningful results.

Yes. The calculator simply computes the duration between any past date and today. You can enter your pet's birth date, a company founding date, or any historical date to find its international age in years and exact day count. The zodiac and Korean age outputs will still display but may not be meaningful for non-human subjects.

Just enter your date of birth in the date picker and the calculator instantly shows the day of the week under Birth Day of Week. The result is computed using JavaScript's Date.getDay() method, which returns a value 0–6 mapped to Sunday through Saturday.