Age Calculator

Calculate your exact age in years, months, and days from your date of birth. Find age differences and upcoming birthday countdowns.

About Age Calculator

How Age Calculation Works

Calculating an exact age is more nuanced than dividing total days by 365. Because calendar months have different lengths (28–31 days) and leap years add an extra day every four years, a precise age must be computed by stepping through each calendar unit individually. The algorithm first counts how many full years have elapsed, then how many additional full months, and finally the remaining days — giving you a result like "32 years, 5 months, and 14 days."

Calendar Systems and Leap Years

The Gregorian calendar, used worldwide today, was introduced by Pope Gregory XIII in 1582 to correct the drift of the Julian calendar. It defines a leap year as any year divisible by 4, except for century years that are not divisible by 400. This means the year 2000 was a leap year, but 1900 was not. These rules are essential for accurate age calculations that span many decades.

Common year: 365 days
Leap year: 366 days (February has 29 days)
Average Gregorian year: 365.2425 days
Leap year rule: divisible by 4, except centuries not divisible by 400

Age Reckoning Around the World

Western System:

In most Western countries, age starts at zero at birth and increments by one on each birthday anniversary. This is the system used by this calculator.

East Asian Age Reckoning:

In traditional East Asian systems (used historically in Korea, China, and Japan), a baby is considered one year old at birth, and everyone gains a year on New Year's Day rather than on their individual birthday. South Korea officially adopted the international age system in June 2023.

Fun Age Facts

A person born on February 29 technically has a birthday only once every 4 years
The odds of being born on a leap day are approximately 1 in 1,461
Your 1-billionth second of life occurs at roughly age 31 years and 8 months
By age 80, the average person's heart has beaten about 3 billion times
The concept of celebrating individual birthdays only became common in the 19th century

Frequently Asked Questions

How does the age calculator determine exact age?

The calculator computes the difference between your date of birth and the current date (or a specified date) by counting full years, remaining months, and remaining days. It accounts for varying month lengths and leap years to give a precise result rather than simply dividing total days by 365.

Does the calculator account for leap years?

Yes. Leap years add an extra day (February 29) every four years, with exceptions for century years not divisible by 400. The calculator handles these correctly when counting months and days, ensuring accurate results for people born on or around February 29.

What happens if I was born on February 29?

If you were born on February 29 (a leap day), the calculator still computes your exact age correctly. In non-leap years your birthday is typically recognized on either February 28 or March 1 depending on jurisdiction, but the mathematical age calculation remains accurate regardless.

How is total days lived calculated?

Total days lived is calculated by finding the absolute difference in milliseconds between your date of birth and today (or the target date), then dividing by the number of milliseconds in one day (86,400,000). This accounts for all leap years and varying month lengths automatically.

Can I calculate the age difference between two people?

You can use this calculator to find each person's age separately and compare the results. For a direct date-to-date difference, try the related Date Difference calculator which is designed specifically for computing the span between any two dates.

Why does my age in months not simply equal years times 12?

Your age in complete months may not be an exact multiple of 12 because the calculator counts only fully elapsed months. For example, if you are 30 years and 4 months old, that is 364 complete months — not 360. The remaining days that have not yet completed a full month are shown separately.

Additional Resources

Leap Year - Wikipedia Gregorian Calendar - Wikipedia Age - Wikipedia

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