Age Calculator
Enter a date of birth and get an exact age — plus the weekday you were born on, your next birthday, and your star sign and Chinese zodiac animal.
🎂 Dates
Defaults to today. Change it to work out an age on any date.
📊 Exact age
🎈 Birthdays
✨ Fun extras
How to use the age calculator
- Enter the date of birth. The field uses your browser’s date picker, and the calculation updates as soon as the date is complete.
- Set the “age at” date. It starts as today, but any date works — a school enrolment cut-off, the date of a photograph, or a birthday in the future.
- Read the exact age in years, months and days, then the totals underneath: months, weeks, days, hours and minutes.
- Check the birthday panel for the weekday you were born on, the date of your next birthday and how many days away it is.
- Look at the fun extras for your star sign and Chinese zodiac animal, and, if you were born on 29 February, choose which day you count as your birthday in common years.
How the calculation works
An exact age is not a single division. Months have 28, 29, 30 or 31 days, so the calculator walks the calendar instead of using an average month length:
- Add whole months to the birth date, one at a time, for as long as the result is still on or before the target date. If the day of the month does not exist in the target month it is clamped to the last day, so 31 January plus one month is 28 or 29 February.
- Divide that count of whole months by 12 to get years and leftover months.
- Count the plain calendar days from the last monthly anniversary to the target date.
| Birth date | Target date | Result |
|---|---|---|
| 1990-01-01 | 2026-09-21 | 36 years, 8 months, 20 days |
| 2024-01-31 | 2024-02-29 | 1 month, 0 days |
| 2023-01-31 | 2023-03-01 | 1 month, 1 day |
| 2000-02-29 | 2025-02-28 | 25 years, 0 months, 0 days |
Total days come from the difference between the two dates measured in UTC, which is why leap days are counted correctly and why time zones never move an answer by a day. Weeks are the total days divided by seven, with the remainder shown separately. Hours and minutes are the day count multiplied by 24 and 1,440 — a deliberate simplification, since real days can be 23 or 25 hours long when the clocks change.
Worked examples
A birthday in January. Born 1 January 1990, measured on 21 September 2026: 36 years, 8 months and 20 days. That is 440 months, 13,412 days or exactly 1,916 weeks. The birth date was a Monday, and the next birthday, 1 January 2027, is a Friday 102 days later.
Born on the 31st. A baby born on 31 January 2024 is one month old on 29 February 2024 — February has no 31st, so the monthly anniversary clamps to the last day. On 1 March the baby is one month and one day old, not two months.
A leapling. Someone born on 29 February 2000 was 25 years old on 28 February 2025 under the default rule, having lived 9,131 days. With the 1 March rule they turn 25 a day later. Their birth date was a Tuesday, and a true 29 February birthday returns in 2028.
Working backwards. Set the “age at” date to a past date to answer questions like “how old was she when this was taken?” — the maths is identical, and the next-birthday panel then refers to that historical date.
Tips and edge cases
- Age cut-offs. Schools, sports leagues and insurers often use a fixed cut-off date. Put that date in the “age at” field rather than today’s date to get the number the form asks for.
- The day itself counts as day zero. On the day you are born you are 0 days old; you reach 1 day the following midnight. That is the same convention hospitals and registrars use.
- Two dates in the same month. If the birth date is later in the month than the target, you get 0 months and a day count — for example 15 March to 2 April is 0 months, 18 days.
- Very old dates. The Gregorian calendar was adopted at different times in different countries, so dates before the 1750s in Britain or the 1920s in Russia may not line up with contemporary records.
- Star sign boundaries move. The sun enters a sign at a specific moment, which shifts by a day or so between years. If a birthday sits on a cusp, treat the sign here as indicative.
Glossary
- Clamping – moving a date to the last valid day of a month when the original day does not exist there.
- Leapling – someone born on 29 February.
- Common year – a year of 365 days, with no 29 February.
- UTC – Coordinated Universal Time, used here so that a calendar date means the same thing everywhere.
Privacy
The calculation runs entirely in your browser. The dates you enter are never uploaded, logged or stored.
Frequently asked questions
How is an exact age calculated?
Count the whole years from the birth date, then the whole months, then the leftover days. Someone born on 1 January 1990 is 36 years, 8 months and 20 days old on 21 September 2026, because 1 January 2026 plus 8 months is 1 September 2026, and 21 September is 20 days later.
How do you handle someone born on the 31st?
Month lengths differ, so a monthly anniversary is clamped to the last day of a shorter month. A baby born on 31 January is one month old on 29 February in a leap year and on 28 February otherwise, and one month and one day old the following day.
When does someone born on 29 February have a birthday?
In leap years, on 29 February. In common years this calculator uses 28 February by default, which matches the usual legal treatment in the UK and most US states. You can switch it to 1 March, the convention in some other countries, and see how the count changes.
Does the calculator use my time zone?
No. Dates are handled as plain calendar dates in UTC, so the answer does not shift if you are in Sydney or Los Angeles. Hour and minute totals assume a flat 24-hour day and therefore ignore daylight saving.
Can I calculate an age on a past or future date?
Yes. The "age at" box defaults to today, but you can set it to any date — useful for school cut-off dates, insurance forms or working out how old someone was at an event.
How accurate is the Chinese zodiac animal?
It is taken from the Gregorian year of birth, which is right for most people. Chinese New Year falls between 21 January and 20 February, so anyone born before it in a given year actually belongs to the previous year's animal.
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