Age Calculator
Calculate exact age from a birth date to any date in years, months, days, and total days lived.
Enter a valid birth date to calculate age.
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How Age Is Calculated
Age calculation is a calendar subtraction problem. The algorithm works in three steps: count full elapsed years, then full elapsed months in the remainder, then remaining days.
Step 1: years = floor((end − start) in days ÷ 365.25)
Step 2: advance start by years, count remaining months
Step 3: remaining days = end − adjusted start
Total days is computed directly as the difference between the two calendar dates, accounting for every leap year between them.
Age Across Cultures and Calendars
In most Western countries, age is counted from zero at birth and increments by one on each birthday. This is called the Western age system.
In the traditional East Asian age system (used historically in China, Korea, and Japan), a person is considered 1 year old at birth and gains a year on the lunar new year rather than their birthday. This can make a person 1–2 years older by East Asian count than by Western count. South Korea officially standardised to the Western system in 2023.
Different calendar systems — Gregorian, Julian, Hebrew, Islamic Hijri — also affect how dates and ages are calculated. This calculator uses the Gregorian calendar, which is the international civil standard.