Age Calculator

Age is the calendar difference between two dates. We compute years, months, and days separately so the result reads naturally — e.g. 25 years, 3 months, 14 days.

age = asOfDate − birthDate

years   = asOf.year − birth.year
months  = asOf.month − birth.month
days    = asOf.day − birth.day

# borrow if day/month is negative
if days < 0:    months -= 1; days += daysInPrevMonth
if months < 0:  years  -= 1; months += 12

1. Subtract the birth year from the current (or "as of") year.
2. Subtract the birth month from the current month. If negative, borrow 1 from the years and add 12 months.
3. Subtract the birth day from the current day. If negative, borrow days from the previous month.
4. Convert the millisecond difference into total days, weeks, hours, and minutes for the secondary metrics.
5. Determine zodiac sign from the birth month/day, and Chinese zodiac from the year mod 12.