Age Calculator
Find exact age in years, months and days on any date, plus total months, weeks and days, the next birthday, and the weekday of birth, with a Feb 29 rule.
Interactive calculator · Method EXACT-AGE-1.0 · Last reviewed: 2026-11-04
Calculate your scenario
Age counts whole calendar months from the birth date: the largest number of months k whose monthly anniversary is on or before the as-of date, shown as k ÷ 12 years and the remaining months; the leftover days run from that anniversary to the as-of date.
Your inputs
Default worked example. Edit the inputs to calculate your scenario.
Default worked example
From 1990-07-15, 435 whole months reach 2026-10-15 (36 years, 3 months), and 20 more days reach 2026-11-04; 13,261 days in all.
How to use the calculator
Enter the date of birth and the date to measure age on, and choose how a Feb 29 (or 31st) anniversary is handled in months that lack that day.
What the result means
Someone born on 1990-07-15 is 36 years, 3 months and 20 days old on 2026-11-04: 13,261 days in all.
Formula and units
Age counts whole calendar months from the birth date: the largest number of months k whose monthly anniversary is on or before the as-of date, shown as k ÷ 12 years and the remaining months; the leftover days run from that anniversary to the as-of date. When the anniversary day does not exist in a month (Feb 29, or the 31st), the selected rule moves it to that month's last day or to the 1st of the next month. Total days is the plain day count between the two dates.
Worked examples
Born 1990-07-15, age on 2026-11-04: Date of birth: 1990-07-15 YYYY-MM-DD calendar date; Age on this date: 2026-11-04 YYYY-MM-DD calendar date; Missing-day rule (Feb 29 birthdays in common years, or a 31st in a shorter month): end.
Example result: Age: 36 years, 3 months, 20 days; Total months: 435 months + 20 days; Total weeks: 1,894 weeks + 3 days; Total days: 13,261; Next birthday: 2027-07-15 (Thursday), in 253 days, turning 37; Day of the week born: Sunday.
Feb 29, 2000 birthday on 2027-02-28 (Mar 1 rule): Date of birth: 2000-02-29 YYYY-MM-DD calendar date; Age on this date: 2027-02-28 YYYY-MM-DD calendar date; Missing-day rule (Feb 29 birthdays in common years, or a 31st in a shorter month): next.
Example result: Age: 26 years, 11 months, 30 days; Total months: 323 months + 30 days; Total weeks: 1,408 weeks + 5 days; Total days: 9,861; Next birthday: 2027-03-01 (Monday), in 1 day, turning 27; Day of the week born: Tuesday.
Limitations and common mistakes
Uses the Gregorian calendar for all dates, with no time of day or time zone, so the as-of date counts as a full day. The as-of date is an input and is not the current date unless you enter it. Legal age rules for Feb 29 birthdays vary by place; the rule here only sets how this calculator counts.
Dividing total days by 365 to get years; leap days make that drift, so use the calendar count of completed years.
Sources and assumptions
Method EXACT-AGE-1.0; last formula review 2026-11-04. Sources and their supported claims. Calculation methodology.