How it's calculated
age = today − date of birth (years, months, days)
Subtracts the birth date from today to give exact age in years/months/days and total days lived. Western zodiac comes from the birth month/day range; Chinese zodiac animal = birth year mod 12.
Common questions
Does it show both zodiac systems?
Yes. It gives your Western sun sign and your Chinese zodiac animal.
Can it tell me the weekday I was born?
Yes. From your birth date it works out which day of the week it was.