Calculator · Windows 10 and 11
Age calculator
Enter a date of birth and see the age four ways: whole years, exact years, months and days, days lived, and days to the next birthday. Change Age on to any day, past or future, for the age a form or a rule asks about. It works on your PC and keeps nothing you type.
How to calculate an exact age
- 1
Open the Age calculator
Open the Calculator and type “age” in Find above the list, or pick Age calculator under Dates and time.
- 2
Enter the date of birth
Type or pick it in Date of birth.
- 3
Choose the day to measure on
Age on starts on today. Change it to a deadline, a cut-off date or a future celebration.
- 4
Read the result
Age gives whole years, Exactly adds months and days, Days lived counts every day, and Next birthday says how many days to go, or Today.
How an exact age is worked out
Age is counted the way a calendar runs: first the whole years since the birth date, then the whole months since the last birthday, then the days since the last monthly date. Someone born on 15 June 1990 is, on 8 October 2026:
- Age: 36 years, because the 36th birthday was 15 June 2026.
- Exactly: 36 years, 3 months, 23 days. Three monthly dates have passed since June (15 July, 15 August, 15 September), and 15 September to 8 October is 23 days.
- Days lived: 13,264, counting from the day of birth to that day.
- Next birthday: in 250 days, on 15 June 2027.
Days lived divided by 7 gives weeks, and divided by 365.25 a rough age with decimals; the calculator does either in one line.
Age on a date that is not today
Many rules ask how old someone is, or will be, on a set date rather than today: school entry, youth sports age groups, a visa or scholarship deadline, a pension or insurance start date, a minimum age on the day of an event. Set Age on to that date. If a school district asks for children who are five by 1 September, for example, set Age on to 1 September of that year and read Age.
The result can hinge on a single day. A child born on 9 October 2010 is 15 years, 11 months and 29 days old on 8 October 2026: still 15 for anything that needs 16, with the Next birthday line showing 1 day to go. For a future date, the same field tells you how old you will be at a wedding, a graduation or a planned retirement.
If you need the gap between two days that are not about a birthday, the days between dates tool also counts weekdays and can include the last day.
Leap-day birthdays and end-of-month dates
People born on 29 February have their real birthday only in leap years. In other years Octoolo counts the birthday as 1 March: someone born on 29 February 2000 is 25 years, 11 months and 30 days old on 28 February 2026, and turns 26 on 1 March. Laws differ on this point between countries, so for official purposes check which day your rules use.
Months of 28 to 31 days force every age calculator to choose a convention near the end of a month, so two tools can disagree about the leftover days for birthdays on the 29th, 30th or 31st. The year count is never in doubt; only the days after it are. Octoolo also works in whole days: the time of birth and the time zone you were born in do not enter into it.
Milestones in days
Days lived makes a few unusual milestones easy to find. A person is 10,000 days old at a little over 27 years and 4 months, a day some people celebrate. A billion seconds arrives at about 31 years and 8 months: divide 1,000,000,000 by the 86,400 seconds in a day and you get just over 11,574 days.
To find the exact date, move Age on forward until Days lived reads the number you want. The same trick finds the day a baby is 100 days old.
Not every culture has counted age the same way. In the traditional Korean system a baby is one year old at birth and everyone gets a year older on New Year's Day; South Korea moved its laws and official documents to the international count, the one Octoolo uses, in June 2023.
Questions, answered
How do I work out my age in days?
Enter your date of birth and read Days lived. It counts every calendar day from your birth date to the Age on date, leap days included.
Can it tell me how old I was on a past date?
Yes. Set Age on to that date; it can be any day after the date of birth, in the past or the future.
What does it show on my birthday?
Next birthday reads Today, and the Exactly line shows your new age with 0 months and 0 days.
How are 29 February birthdays handled?
In years without a 29 February, the birthday is counted on 1 March.
Does it keep the dates I type?
No. Nothing you enter is saved or sent anywhere; close the Calculator and the dates are gone.
Why does it say the date of birth is after that day?
Age on is set earlier than the date of birth. Move one of the two dates and the answers come back.
Age calculator, and 16 more apps.
Download for Windows7 days free, then from $3.99 a month for all 17 apps. Windows 10 and 11.