To calculate your age, enter your birthday in Date of Birth. Calculate Age On is already set to today, so the result appears straight away; select Calculate Age if it doesn't. You get your exact age in years, months and days, the total days you've lived, and a countdown to your next birthday.
How to use the age calculator
- Enter the date of birth. Pick it in the Date of Birth field. The calculator starts working as soon as both date fields have a value.
- Choose the date to measure to. Calculate Age On defaults to today. Change it to any other date to find someone's age on that day, or select Use Today to switch back.
- Read the results. The summary row shows exact age and totals from days to seconds. Main Age Results adds your next birthday, retirement date and working days lived.
- Copy or reset. Select Copy Summary to copy every result as plain text, or Clear All to start again.
How an age calculator by date of birth works out your age
The calculator counts whole years first, then whole months, then the days left over. If the day of the month hasn't come round yet, it steps back one month and counts the real days from that month's matching date (or its last day, if that month is shorter), so the day figure is never negative. Totals count whole calendar days, so a daylight saving change can't add or drop a day.
Example: someone born on 14 June 1998 is 28 years, 3 months and 27 days old on 11 October 2026. From 14 June 1998 to 14 June 2026 is 28 years. From 14 June to 14 September is 3 months. September has 30 days, so 14 September to 11 October is 27 days. That's 10,346 days in total, with the next birthday 246 days away.
If you were born on 29 February, the calculator treats 28 February as your birthday in years that aren't leap years.
Age on a specific date
The second field doesn't have to be today. Set Calculate Age On to any date after the birth date and every result updates for that day. Use it to check:
- How old you'll be on a trip, wedding or exam date.
- Whether a child meets a school or sports age cut-off, such as 1 September.
- When you reach a retirement age. Set Retirement Age between 40 and 100 (60 is the default) to see the date and the time left.
A birth date later than the target date shows an "Invalid date range" message. To count the days between any two dates, use the days between dates calculator.
Chronological age calculator for school and test reports
Chronological age is simply your age since birth, written as years, months and days. Psychologists and speech therapists record it on the test date, because standardized scores compare a child with others of the same age.
To work it out by hand, subtract the birth date from the test date: days, then months, then years. Some test publishers use a fixed rule when they borrow: Pearson's WIAT-III manual, for example, says all months are treated as having 30 days and ages are not rounded up. This calculator borrows the real length of the month instead, so its answer can differ by a day or two.
| Birth 25 Mar 2018, tested 10 Aug 2026 | Result |
|---|---|
| 30-day month rule (test manuals) | 8 years, 4 months, 15 days |
| Real month length (this tool) | 8 years, 4 months, 16 days |
For an official score report, follow the rule in your test's manual.
Age of a baby or child in months, weeks and days
For babies, the summary row is often more useful than the years figure. A baby born on 20 July 2026 is 2 months and 21 days old on 11 October 2026. The summary also shows 83 total days, 11 total weeks and 2 total months. Weeks and months only count fully completed ones, so 83 days shows as 11 weeks, not 12.
To find a child's age on a past day, set Calculate Age On to that date.
Extra results: birthdays, planets and life estimates
Along with the core age, the calculator shows your birth weekday, zodiac sign, half birthday and the date you turn 10,000 days old (30 October 2025 for the June 1998 example).
Four switches add optional estimates: planetary age (Mercury to Neptune, from each planet's orbital period), working days lived, total sleep, and heartbeats and breaths. They multiply the time you've lived by averages you can change, such as 8 hours of sleep and 72 heartbeats a minute, so treat them as rough figures. The working-days count ignores holidays and leave.
Frequently asked questions
How old am I today?
Enter your date of birth in the calculator above. With the second date left on today, it shows your exact age in years, months and days and the total days you've been alive. Nothing is sent to a server.
How do I calculate age by date of birth?
Subtract the birth year from the current year, then take off one if this year's birthday hasn't happened yet. For months and days too, enter the date of birth above and the calculator does the borrowing.
Can I find my age on a past or future date?
Yes. Change Calculate Age On to any date after the birth date. All results, including total days and the next birthday, are recalculated for that date.
How is chronological age calculated for testing?
Subtract the date of birth from the test date in days, months and years. Some test manuals, such as Pearson's WIAT-III, treat every month as 30 days when borrowing and never round up, so check your manual's rule for official reports.
Can it work out a baby's age in weeks?
Yes. The summary row shows total days, total weeks and total months alongside the exact age. Only completed weeks and months are counted.
Is there a dog age calculator?
This tool calculates human age only. As a rough guide, the American Veterinary Medical Association says a medium-sized dog's first year equals about 15 human years, the second about 9, and each year after that about 5.
Are the heartbeat and sleep figures accurate?
No. They multiply the time you've lived by the averages you enter. This calculator gives estimates, not medical advice. The BMI calculator is another estimate, based on height and weight.