Age Calculator

How to calculate your age

An age calculator answers a simple question: how much time has passed between your date of birth and another date? Most people want the answer in years, months, and days. This page gives that answer, plus the total time you have lived in months, weeks, days, hours, minutes, and seconds, the day of the week you were born, and a countdown to your next birthday.

How to use this age calculator

Enter your date of birth, then check the age-at date. It starts as today, so you will see your current age straight away. Change the age-at date if you want to know how old you were on a past date, or how old you will be on a future date, such as a wedding, a graduation, or a retirement date. The result updates as you type. If a date is invalid, or the birth date is after the age-at date, you will see a clear message instead of a wrong answer.

How age in years, months, and days is calculated

The calculation counts complete units, starting from your last birthday. First, it finds your most recent birthday on or before the age-at date. The years are the number of birthdays since you were born. Then it counts complete months from that birthday to the age-at date, and finally the remaining days. That is why the months and days parts are never just the difference between the two months or the two days on their own: a month is only counted once it is complete, and days are borrowed from the previous month when needed, just as in ordinary calendar arithmetic.

Worked example

Take a birth date of 15 January 2000 and an age-at date of 10 March 2026. The last birthday was 15 January 2026, which is 26 years after birth. From 15 January to 10 March is one complete month, to 15 February, plus 23 days, because February 2026 has 28 days and 10 March is 23 days after 15 February. The age is therefore 26 years, 1 month, and 23 days. The total days lived are the calendar days from 15 January 2000 to 10 March 2026, and the total weeks, hours, minutes, and seconds are worked out from that day count.

Leap-year birthdays: February 29

A leap year is a year divisible by 4, except century years, which must also be divisible by 400. That is why 2000 and 2024 were leap years, but 1900 and 2100 are not. If you were born on 29 February, you only have a 29 February birthday in leap years. In other years, this calculator treats 1 March as your birthday for the age count and the countdown, and it tells you plainly whether your next birthday is a leap-year birthday on 29 February or not, so there is no surprise in the result.

Time zones and local dates

Many online calculators get this wrong by one day. A date entered as text is often read as midnight in UTC, which is still the previous day in much of the Americas. This calculator avoids that by working on calendar dates in local time: the date you type is the date that is used, wherever you are. That matters most for birthdays, where a one-day shift changes both the age in days and the day of the week you were born.

What the totals mean, and common mistakes

Total months means complete months lived, which is the years multiplied by twelve plus the months part of your age. Total weeks are whole weeks in the total days, and total hours, minutes, and seconds are whole-day totals, because no time of birth is entered. A common mistake is entering a future birth date, which cannot give a real age, or swapping the two dates. Another is counting both the start and end dates when working out days between dates, which adds one day too many. For any two dates that are not a birth date, use the date difference calculator or the days between dates calculator instead, so the wording matches what you are actually measuring.