Age Calculator

The Age Calculator answers one precise question: exactly how old is someone, down to the day. Enter a birth date, optionally set an "age at" date other than today, and it returns the age split into completed years, remaining months, and leftover days, plus totals for days, weeks, and hours lived.

The interesting part is the calendar arithmetic. Months run from 28 to 31 days and leap years insert a February 29th, so dividing total days by 365 gives the wrong answer. This tool counts the way a person counts by hand: it subtracts full years first, then full months, then borrows the actual number of days from the specific preceding calendar month when the birth day falls later in the month than the target day. Because it borrows real month lengths rather than assuming a flat 30 days, the "years, months and days" figure matches how age is recorded on official forms, and it stays correct across leap years and awkward month-end birthdays like the 31st.

Everything runs locally in your browser using JavaScript's built-in date handling. Your birth date is never uploaded and nothing is stored on a server, which matters because a date of birth is a common identity-verification detail. Once the page has loaded, it keeps working offline.

The uses are concrete. Fill in forms that demand age in years and months. Check whether a child clears a school-entry or youth-sport age cut-off on a specific date. Confirm eligibility for a pension, licence, or age-gated service. Track an infant's age in weeks, work out a pet's age, or compute a person's age at death from two historical dates for genealogy.

A useful trick: set the "age at" date to a future birthday and read the total-days figure to see exactly how many days remain until it. Set it to a past event to find how old you were on that specific day. Change either date and recalculate as often as you like; each run is independent and nothing is saved between them.