Age Calculator

How age is calculated

Age seems simple — it is the number of years since your birth — but the exact calculation depends on how you handle leap years and partial years. The most accurate approach uses the total number of elapsed days and divides by 365.25 (the average length of a year accounting for leap years).

The reason to use 365.25 rather than 365 is that leap years (with 366 days) occur roughly every 4 years. Over a lifetime, ignoring this adds up: someone born on 1 January 1960 who is 64 years old has lived through 16 leap years, a total of 16 extra days not accounted for by a simple 365-day calculation.

Age across cultures and legal systems

While the Western convention treats newborns as age 0 and adds 1 on each birthday, other systems differ significantly. Traditional East Asian age-reckoning (sometimes called “Korean age” or “Chinese age”) considers a person to be 1 at birth, and everyone gains a year on New Year's Day rather than on their individual birthday. Under this system, someone born on 31 December would be 2 years old two days later.

South Korea officially transitioned away from this system in June 2023, standardising on the international system. However, traditional age reckoning remains culturally embedded in many contexts.

Legal age thresholds

Biological vs. chronological age

Your chronological age — the number you calculate here — is simply how long you have been alive. But scientists increasingly distinguish this from biological age: how well your cells and organs are actually functioning relative to a healthy baseline.

Lifestyle factors — exercise, sleep, diet, stress management, and not smoking — can make biological age significantly younger than chronological age. Research suggests regular aerobic exercise alone can reduce biological age markers by up to 10 years compared to a sedentary lifestyle.

Fun facts about age and time

• You are older in space. Astronauts age fractionally faster at orbital altitudes due to gravitational time dilation (special relativity). After a 6-month mission, they are a fraction of a millisecond older than if they had stayed on Earth.
• Your cells are much younger than you are. Most of the cells in your body are replaced regularly. Gut epithelial cells are replaced every 2–5 days; red blood cells every ~120 days; most liver cells every 300–500 days. Some neurons, however, last a lifetime.
• The oldest verified human lived 122 years. Jeanne Calment of France (1875–1997) holds the verified record for human longevity. She was born before the invention of the telephone.
• A year is not exactly 365.25 days. The tropical year (one orbit around the sun) is 365.24219 days. The Gregorian calendar corrects for this with a leap year every 4 years, except centuries not divisible by 400 — which is why 2000 was a leap year but 1900 was not.

Calculates your exact age in years, months and days from your date of birth to today. Also shows your age in total days, weeks and months for fun statistics.