“How old am I?” sounds trivial until leap days, month lengths, and time zones disagree. The age calculator answers with completed calendar years, months, and days between two dates you choose—plus a separate total-day count that does not try to redefine the Y/M/D label.

The worksheet does not guess “today” from a server clock. You select the as-of date so a traveler near a date line—or a form that needs age on a past deadline—gets a reproducible answer. Inputs are date-only values aligned with civil Gregorian dates (see RFC 3339’s discussion of date formats).

When the birth date is February 29 and the as-of year is not a leap year, this site clamps the anniversary to February 28 for the year/month/day decomposition. That is calculator policy for deterministic math—not a claim that every legal system does the same. Always read local rules when age gates a right or obligation.

Need the length of a contract in calendar days? Use days between dates and match inclusive rules. Need business days excluding weekends and holidays you list? Use working days. Need “N days from a start date”? Use the date calculator. Age is the wrong tool for those jobs.