How Is Exact Age Calculated? Chronological Years, Months & Days

Calculating your exact age sounds straightforward, but varying month lengths (28, 29, 30, or 31 days) make precise subtraction tricky.

The Chronological Subtraction Algorithm

To compute exact age as Years, Months, and Days:

1. Subtract the birth day from the current day. If negative, borrow the total number of days from the previous month and subtract 1 from the current month.
2. Subtract the birth month from the adjusted current month. If negative, borrow 12 months from the current year and subtract 1 from the year.
3. Subtract the birth year from the adjusted current year.

Leap Day Birthdays (Feb 29)

In non-leap years, legal systems vary:

• In the UK and Australia, someone born on Feb 29 officially turns a year older on March 1.
• In the United States and Canada, common law recognizes the completion of the year on February 28 for contractual milestones.

Calculate Your Exact Age Now

Skip the mental math — our [Age Calculator](/date-time/age-calculator) applies the borrow-month algorithm above to show your exact age in years, months, days, hours, minutes, and seconds, plus your next birthday countdown, zodiac sign, and life milestones.