How it's calculated
age = reference date − birth date (years, then months, then days)
Counts whole calendar years from birth date to the reference date, then the leftover months and days. Also totals the gap in months, weeks and days, plus days until the next birthday.
Common questions
How do you calculate age in years, months, and days?
Count whole years to the most recent birthday, then the months and remaining days, adjusting for leap years and the varying length of each month.
Why does the day count vary between months?
Months range from 28 to 31 days, so the leftover days after counting whole months depend on which months the period spans.