How to use the age calculator
Enter a date of birth and the calculator shows the exact age today in years, months and days, together with the same span in total months, weeks, days, hours, minutes and seconds. The seconds figure ticks live. Hours and seconds count from midnight on your birthday unless you add a time of birth, in which case they count from that moment. If you were born abroad, pick the time zone you were born in so the birth moment is placed correctly — a birth at noon in Delhi happened five and a half hours before noon in London.
To find someone's age on another date — the day a form needs signing, a school cut-off date, the start of a holiday — change Age on this date. It works for past and future dates, so you can check how old a grandparent was on their wedding day or how old you will be at retirement. The Today button puts it back.
Below the main result you'll find your next birthday with its weekday and a countdown, facts about the day you were born, upcoming milestones such as your 10,000th day, and a separate calculator for the age difference between two people. Copy summary gives you a plain-text version. Nothing you enter is stored or sent anywhere.
How exact age is counted
Age in years, months and days is counted the way people do it on a calendar, not by dividing days by 365.25. First the calculator counts whole years up to your most recent birthday, then whole months from that birthday, then the remaining days. For someone born on 15 May 1990, on 24 September 2026 that is 36 years (to 15 May 2026), 4 months (to 15 September) and 9 days.
Month lengths vary, so a “month” is counted to the same day number in the next month. When that day doesn't exist — the 31st in a 30-day month, or 29 February — the last day of the month is used. So from 31 January, one month later is 28 February (or 29 in a leap year).
| Measure | How it is calculated |
|---|---|
| Years, months, days | Calendar counting, as above |
| Total months | Years × 12 + months (a “+” means part of a month more) |
| Weeks and days | Exact days ÷ 7, with the remainder |
| Hours, minutes, seconds (to today) | Real time elapsed from the moment of birth to now, including every GMT/BST clock change |
| Hours, minutes, seconds (to another date) | Calendar days × 24, from the time of birth to the start of that date |
Years, months and days are worked out on whole calendar days rather than clock timestamps. That avoids a classic bug in date calculators, where a clock change or a time-zone offset makes a date slip by one day and a birthday appears a day early or late. The live hours and seconds are different: they measure real elapsed time, so someone born at noon in January has lived one hour less than “days × 24” at noon in British Summer Time. The method matches the widely used python-dateutil library, and the results were checked against it on more than 80,000 date pairs.
Leap-day birthdays
About one person in 1,461 is born on 29 February, which only occurs in leap years: years divisible by 4, except century years not divisible by 400. So 2000 was a leap year but 1900 and 2100 are not. In the other three years, a leapling's birthday has to fall on either 28 February or 1 March.
There's no worldwide rule. In the UK, a person born on 29 February is generally treated as reaching a new age on 1 March in a non-leap year for legal purposes, and that is the calculator's default. Some countries, including New Zealand and Taiwan, use 28 February instead, and many leaplings simply celebrate on whichever day they prefer. If you enter a 29 February date of birth, a switch appears so you can choose; your age, countdown and milestones all follow your choice. Months are still counted from the 29th: a leapling is 1 year, 9 months and 29 days old on 28 December, because the last monthly anniversary was 29 November. With the 1 March rule, 28 February in a non-leap year reads 11 months and 30 days, and 1 March is the birthday itself. The calculator also tells you how many 29 Februarys you have lived through.
Birth weekday, star signs, Chinese zodiac and milestones
- Day of the week. Worked out from the date itself, for any year from 1000 to 9999. Britain switched from the Julian to the Gregorian calendar in September 1752, when Wednesday 2 September was followed by Thursday 14 September. Dates before 14 September 1752 are shown on the modern calendar (what historians call proleptic Gregorian), and the calculator says so when you enter one, because records from the time give a date 10–11 days earlier.
- Star sign. The tropical western zodiac used in newspaper horoscopes, from Aries (21 March–19 April) to Pisces (19 February–20 March). Dates on the cusp can shift by a day from year to year.
- Chinese zodiac. The animal and element change at Lunar New Year, which falls between 21 January and 20 February, not on 1 January. Anyone born in January or early February may belong to the previous year's animal. The calculator works out the actual Lunar New Year date for the year you were born from astronomical new-moon calculations and tells you which side of it you fall.
- Milestones. Your 10,000th day arrives at about 27 years and 4 months; one billion seconds at about 31 years and 8 months. The list shows the next few milestones with dates and how many days away they are.
Need to count down to one of those dates? Set an online timer, or use the BMI calculator alongside your age for a quick health check.
Frequently asked questions
How do I calculate my exact age?
Count the whole years to your last birthday, then the whole months since that birthday, then the days left over. If you were born on 15 May 1990, on 24 September 2026 you are 36 years, 4 months and 9 days old. Enter your date of birth above and the calculator does this instantly, including leap years and months of different lengths.
How many days old am I?
Enter your date of birth and read the days figure, which counts every calendar day from your birth date to today. It includes every leap day you have lived through. The same panel shows your age in weeks, hours, minutes and a live seconds count. Add your time of birth to make the hours and seconds exact.
When is my birthday if I was born on 29 February?
In leap years it is on 29 February. In other years, the UK generally treats 1 March as the day you legally turn a year older, while some countries use 28 February. The calculator defaults to 1 March and lets you switch, and your countdown and milestones follow whichever you choose.
Can I work out someone's age on a specific date?
Yes. Change the “Age on this date” box to any past or future date. That's useful for forms asking for your age on a set day, school admissions, insurance, or finding out how old a relative was at a family event. Press Today to measure to the current date again.
Why is my Chinese zodiac animal different from what I expected?
The Chinese zodiac year starts at Lunar New Year, which moves between 21 January and 20 February, not on 1 January. If you were born before Lunar New Year in your birth year, your animal is the previous year's. The calculator shows the Lunar New Year date for your birth year so you can see which side you fall.
Does the age calculator store my date of birth?
No. Your date of birth is used only in your browser to do the calculation and is never sent anywhere or saved. The only preference remembered is your choice of 28 February or 1 March for leap-day birthdays. Close the tab and the dates you entered are gone.