How to Calculate Your Exact Age

What exact age means

Most people give their age in whole years, but an exact age also includes months and days. Someone born on 15 June 1990 is 36 years, 4 months and 7 days old on 22 October 2026. It is the same information as the date of birth, written as a duration.

Exact age matters for forms that ask for age in months, for infants and toddlers, for eligibility rules with a cut-off date and for simple curiosity. It also gives you the number of days you have lived, which is a fun figure: 13,278 days in this example.

The method: years, then months, then days

Count complete years first. From 15 June 1990, the last birthday before 22 October 2026 was on 15 June 2026, so the age is 36 complete years. Then count complete months from that birthday: July, August, September and October make 4 months, ending on 15 October 2026. The remaining days from 15 October to 22 October are 7.

The result is 36 years, 4 months and 7 days. The order matters. Counting months and days from a birthday is the usual convention, and it gives a different result from dividing the total number of days by 365 or 30.

Total months lived is 36 × 12 + 4 = 436, and total weeks is the number of days divided by 7, rounded down: 1,896 weeks in this example.

Days lived and the next birthday

To find the number of days lived, take the days between the date of birth and today. For the example it is 13,278 days. A birthday is mostly a calendar event, so the number of days between birthdays is 365 or 366, depending on whether a leap day is in between.

The next birthday is the next time the day and month occur. For 15 June 1990, the next one after 22 October 2026 is 15 June 2027, a Tuesday. If today is the birthday, the next birthday counts as today, so the countdown is zero days and the calculator says so.

Knowing the weekday of the day you were born is a classic trivia question. 15 June 1990 was a Friday. The calculator shows it on the age tab.

Leap-day birthdays

People born on 29 February have a birthday only every fourth year. In the other years, a calculator needs a rule. This one places the birthday on 28 February in years without a leap day. Some people prefer 1 March, and the choice is a matter of convention that can differ by country and by purpose.

The exact age is not affected by the choice, because it is counted in complete years and months from the date of birth. Someone born on 29 February 2000 is 27 years old on 28 February 2027 in this system, and the same age on 29 February 2028.

Leaplings often count their birthdays in leap years, which makes them very young by that count, but legal ages follow the calendar.

Different ways of counting age

Age in complete years is the international norm. Other systems exist. South Korea used a traditional age that made a baby one year old at birth and added a year every 1 January, together with other age systems used for particular purposes, until a new law on 28 June 2023 made the international age the standard for most official uses.

In Japan, the law on counting age says that a person reaches a new age at the end of the day before the birthday. A child born on 1 April therefore turns six at the end of 31 March and begins school with the earlier year group, which is why 1 April births are counted among the early-born.

These examples show that age is a calculation with rules, not just a number. For everyday use, the international method of complete years from the date of birth is what a date calculator uses.

Practical uses

Age calculators are used for age-limited services and eligibility, school entry and cut-off dates, insurance and pension forms, medical questionnaires that ask for age in months, and sports categories. Always check the reference date that the rule uses, because a cut-off may refer to age on a fixed date and not to age today.

The second field on the age tab lets you set that date. Enter the date of birth, then set Age on to the cut-off date, and you get the exact age on that day. Use it to check whether a child is old enough on the first day of a school year or an event.

Using the calculator

Open the Age tab, enter the date of birth, and the age appears at once in years, with the exact breakdown, the months, weeks and days lived, the weekday of birth and the next birthday below it.

Everything is calculated in your browser, and the date of birth is not sent anywhere. For a date of birth, which is personal information, that is the right way to do it.