The algorithm uses calendar date arithmetic rather than millisecond timestamp subtraction. This avoids common pitfalls - daylight saving time changes, time zone differences, and millisecond drift across leap seconds don't shift the result. The calculator computes the difference in three nested steps: first the completed years (target year minus birth year, adjusted if birth month/day hasn't passed in target year), then the completed months remaining, then the remaining days.
For leap year edge cases: a birth on 29 February in a year like 2000 means the next 'true' birthday is 29 February 2004, but for legal and practical purposes in non-leap years, the date is treated as 28 February (this is the convention used by most Indian government forms and exam boards). The calculator also handles months of different lengths gracefully - going from 31 January to 28 February is exactly one month, not 28 days.
Beyond the years-months-days breakdown, the calculator computes total days, weeks, hours, minutes and seconds of age. These extended formats are useful for milestone celebrations ('I'm 10,000 days old today!'), insurance underwriting, retirement planning, or just curiosity. Days until next birthday is also computed so you know exactly how long until your next celebration.