Age Calculator

Calendar-style age breakdown, the same way you would count on your fingers:

1. Tentatively take the year, month, and day differences: $\text{years} = \text{refYear} - \text{birthYear}$, $\text{months} = \text{refMonth} - \text{birthMonth}$, $\text{days} = \text{refDay} - \text{birthDay}$.
2. If the day count is negative, the reference day has not yet caught up to the birth day this month — borrow the days of the previous month and subtract one from the months count.
3. If the months count is then negative, the reference month is still before the birth month this year — borrow 12 months and subtract one from the years count.
4. Compute total elapsed days from the raw timestamps: $\text{totalDays} = \Delta t / 86400000$; minutes and seconds are derived from that whole-day count.
5. Find the next birthday by setting the year of the birth month-and-day to the reference year (or the next year if that anniversary has already passed) and counting the days remaining.