Exact age in years, months and days, plus your next birthday.
Calendar months are unequal in length so the y · m · d breakdown rolls over from the day of the month, not from a fixed 30-day average.
Saying "I am 35" hides a lot. It hides that you are 35 years and 7 months and 12 days, that you have lived 13 010 days, that your next birthday is 142 days away, and that you were born on a Friday. None of those numbers are essential to daily life, but each one shows up surprisingly often: legal forms ask for an age "as of" a specific date, gestation and child development are tracked in weeks, milestone-tracking apps want exact days, and birthday-planning apps want a countdown. A naive "current year minus birth year" calculation gets the answer wrong half the year because it ignores whether the birthday has already passed. This calculator removes the ambiguity by computing a calendar-aware diff: years, months and days as the calendar actually rolls, plus a handful of useful aggregates (total days, weeks, hours, minutes), the day of the week of birth, and the date and distance of the next upcoming birthday.
Age in years / months / days is a calendar diff, not a fixed-length subtraction. The algorithm: take the day-of-month of the reference date and subtract the day-of-month of the birth. If the result is negative, borrow from the months column by adding the day count of the previous month of the reference date. Then subtract months. If months is negative, borrow from years by adding 12. The remaining year delta is the age in completed years. This matches how civil law and pediatric tracking handle ages — "still 5 until the actual day", not "rounded up". Total days, total weeks, total hours and total minutes are derived from the millisecond difference: (ref − birth) / 86 400 000 for days, with × 7, × 24, × 60 derivations stacked on top. Next birthday is the upcoming anniversary: take the birth's month and day, anchor them to the reference year, and bump to the next year if that date has already passed.
Pick your date of birth. Optionally set an as-of date if you want the age on a specific historical or future date — leave it blank for today. The calculator returns the y · m · d breakdown, the four aggregate counts, the day of week of birth (handy trivia: it's also the answer to "what day was X born on?"), and the date of the next birthday with a countdown in days. Toggle between examples (an adult, a toddler, an elderly person) to see how the numbers change at different scales.
Birth date 15 June 1990, reference date 2 May 2026. - Day diff: 2 − 15 = −13 → borrow 30 days from April: 30 + 2 − 15 = 17 days. Months: −1 (April vs June, post-borrow) → borrow 12: months = (5 − 6 + 12) − 1 = 10. Years: 2026 − 1990 − 1 (because the June birthday hasn't happened yet) = 35 years, 10 months, 17 days. - Total days: from 1990-06-15 to 2026-05-02 inclusive of leap years = 13 105 days, ≈ 1 872 weeks, ≈ 314 520 hours, ≈ 18 871 200 minutes. - Next birthday: 15 June 2026 — 44 days away. - Day of week of birth (15 June 1990): Friday.
Time zones. The calculator uses UTC midnight throughout. If you were born in one time zone and live in another, the day-of-week of birth might differ by one. For all civil purposes use the date as recorded on your birth certificate; treat the day-of-week as trivia, not an identity-document check.
Leap days. Born on 29 February? In non-leap years, your "anniversary" is normally observed on 28 February (in some legal systems) or 1 March (in others). The calculator anchors strictly to month-and-day, so for a 29-Feb birth in a non-leap reference year it will show the next 29 February — i.e., the legal next-birthday date in the most-common civil-law convention. Adjust the as-of date if your jurisdiction uses 28 Feb instead.
Borrow logic for tail-end days. Comparing 2026-03-30 to a birth on 2025-12-31 yields 2 months and 30 − 31 = −1 days. The borrow from February (28 in 2026) gives 28 + 30 − 31 = 27 days. The result, 0 y · 2 m · 27 d, is correct but counter-intuitive — anniversaries near month boundaries can produce odd-looking decompositions because months have unequal lengths. The total-days count (89 days) is the unambiguous summary.
Future birth dates. If the reference date precedes the birth date the calculator returns nothing — there is no defined "negative age" in this product. Use a date arithmetic calculator if you need that.