How Age Is Calculated

Age calculation seems simple — subtract the birth year from the current year — but the exact calculation in years, months, and days requires careful handling of varying month lengths and leap years.

The Algorithm

1. Subtract birth year from target year to get years
2. Subtract birth month from target month to get months
3. Subtract birth day from target day to get days
4. If days are negative, borrow from the previous month (using its correct number of days)
5. If months are negative after borrowing, borrow from years (add 12 months, subtract 1 year)

Leap Years

A leap year occurs every 4 years, except for years divisible by 100 (unless also divisible by 400). So 2000 was a leap year, but 1900 was not. February has 29 days in a leap year instead of 28. This affects age calculations for anyone born on or around February 29.

Zodiac Signs