Age Calculator
Enter a date of birth to get an exact age in years, months and days, plus the total in weeks and days and a countdown to the next birthday.
🔒 Runs entirely in your browser. Nothing you enter is sent to a server.
How old are you, exactly? Not just in years, but in months, weeks and days? This age calculator works it out from your date of birth, for today or for any other date you choose. It also tells you which day of the week you were born on and how long until your next birthday.
How to use the age calculator
- Enter the date of birth.
- Leave “Age on this date” blank to use today, or pick another date to find an age in the past or the future.
The results show the exact age in years, months and days, the same age expressed in months, weeks and days, the date of the next birthday with a countdown, and the weekday of birth.
How the age is worked out
Calculating an age by hand is fiddly because months have different lengths. The calculator follows the same method people use on paper:
- Count whole years. Count the birthdays that have passed.
- Count whole months. Count how many monthly anniversaries have passed since the last birthday.
- Count the days. Count the days since the last monthly anniversary.
If a birthday falls on a day that does not exist in a shorter month, such as the 31st, the last day of that month is used. Totals in weeks and days come from the exact number of days between the two dates:
Days = end date − date of birth
Weeks = Days ÷ 7, with the remainder shown as daysWorked example
Someone born on 15 May 1990, calculating their age on 28 October 2026:
- Birthdays passed: 1991 to 2026, so 36 years. The last one was 15 May 2026.
- Monthly anniversaries since then: 15 June to 15 October, so 5 months.
- Days from 15 October to 28 October: 13 days.
- Exact age: 36 years, 5 months, 13 days.
In total that is 13,315 days, or 1,902 weeks and 1 day. They were born on a Tuesday, and their next birthday, on Saturday 15 May 2027, is 199 days away.
When an exact age matters
- School admissions. Many schools require a child to reach a certain age by a cut-off date. Enter the cut-off as the “age on” date.
- Retirement and pensions. Find the exact date you reach a pension age, or how old you will be on a planned retirement date.
- Sports and competitions. Age groups are often based on age on a set date, such as 31 December or 1 January.
- Visas, insurance and forms. Some applications ask for age in completed years on a specific day.
- Milestones. Plenty of people celebrate 10,000 days old, which arrives at about 27 years and 4 months.
Tips and pitfalls
- Age in East Asian systems can differ. Traditional Korean age counting, for example, started at 1 at birth. South Korea officially switched to the international method in 2023, but you may still see the older system used socially.
- Time zones can shift a birthday. If you were born late at night in one country and now live in another, your birthday may begin on a different calendar day. The calculator works with calendar dates only.
- Leap years are handled automatically. The total in days includes every 29 February between the two dates.
- Babies and corrected age. For premature babies, doctors often use corrected age, which subtracts the weeks born early. This calculator shows chronological age.
Nothing you enter is stored or sent anywhere. The calculation happens entirely in your browser.
Frequently asked questions
How is age calculated?
Age is the number of complete years since the date of birth, followed by the complete months since the last birthday and the days since the last monthly anniversary. You gain a year on your birthday, not before.
How does the calculator handle a birthday on 29 February?
In years without 29 February, the calculator treats 28 February as the birthday. Legal rules differ between countries. In the UK and some other places a person born on 29 February legally turns a year older on 1 March in common years.
Can I calculate an age on a past or future date?
Yes. Fill in the "Age on this date" field with any date after the date of birth. This is useful for school entry cut-offs, retirement planning, insurance forms and eligibility checks.
Why do different websites give a slightly different age in days?
Some count the birth date and the end date as two separate days, and some do not count time zones the same way. This calculator counts the full days between the two dates, so a baby born yesterday is 1 day old.
What is chronological age?
Chronological age is simply the time since birth, which is what this calculator shows. It is used in school and medical assessments to tell it apart from developmental or corrected age, for example for premature babies.