How the age gap is calculated
The calculator first determines the age of each person as of today (or a specified reference date) in years, months, and days. The age difference is then the absolute difference between those two ages. To find the difference in total days, it subtracts the later birth date from the earlier birth date directly using Julian day numbers, which accounts correctly for all month lengths and leap years.
The years-and-months breakdown uses the same calendar stepping as age calculation: whole years are counted by stepping the year forward, then remaining months are counted by stepping the month forward, and remaining days fill the last partial month.
Age gap (days) = |Birth date 1 (Julian day) − Birth date 2 (Julian day)|
The absolute number of days between the two birthdays.
Age gap (years) = Floor(Age gap (days) ÷ 365.25)
An approximation; the exact figure uses calendar stepping.