How age calculator Works
How age counting works
Legal age counts completed years (you are 0 until your first birthday), then the remainder expresses as months and days. The borrowing rule matters: when the current day-of-month is earlier than the birth day-of-month, a month is borrowed and days are counted against the PREVIOUS month's length — 28 through 31 days depending. The calculator implements exactly this convention.
Days lived: the perspective machine
Total days lived is the counter people did not know they wanted: ~10,000 days at 27, ~20,000 at 54. It converts an abstract age into a countable quantity — the basis of "day counting" gratitude practices and the reason 10,000-day birthdays are a thing worth marking.
Leap years and the edge cases
February 29 birthdays technically occur once per four years — most jurisdictions celebrate March 1 in common years (or Feb 28; laws vary). The calculator handles leap-day births by counting to Feb 28 in common years. Age at a future date, half-birthdays, and pet years all run on the same underlying date math this page implements.