Age Calculator

About the Age Calculator

Enter your date of birth and this calculator returns your exact age in years, months and days — not a rounded figure, and not a decimal. It counts the way people actually count age, respecting how long each individual month happened to be.

You also get the totals: how many days, weeks, hours and minutes you have been alive. Alongside those sit the weekday you were born on, the date of your next birthday, and how many days remain until it. The Hijri date of your birth is shown too, for anyone who needs it.

By default it measures to today, but you can set any date in the "age on" field. That is useful for checking an age at a past deadline, or working out how old someone will be on a future date — for a school cut-off, a visa application, or an insurance form.

How to use the Age Calculator

1. Pick your date of birth.
2. Leave the second date as today, or set it to work out your age on any other date.
3. Select Calculate my age.
4. The totals convert your age into days, weeks, months and hours.
5. Your Hijri birth date is shown alongside.

How exact age is calculated

Age is not days divided by 365.25. It is a calendar count: how many full years have passed since your birthday, then how many full months since that anniversary, then the leftover days.

Why the borrowing step matters

Because months are not the same length, and treating them as 30 days each quietly introduces errors. Consider someone born on the 31st:

The third row is the one that catches people out. Someone born on a leap day has not technically had their 24th birthday on 28 February 2024 — it arrives the next day. Whether that matters depends entirely on the legal context.

Leap years and your day count

A leap year adds 29 February, so it runs 366 days instead of 365. The rule has three parts: divisible by 4 is a leap year, unless divisible by 100, unless also divisible by 400. That is why 2000 was a leap year and 1900 was not.

Leap days do not change your age — you still have one birthday a year — but they do change your total day count. Over a 40-year life you accumulate roughly ten extra days from leap years alone, which is why the totals here are counted from real calendar dates rather than estimated from an average year length.

These are averages. Your own total depends on how many leap days fell inside your lifetime and exactly where your birthday sits, which is why the calculator counts real dates instead of multiplying.

Finding the weekday you were born on

The Gregorian calendar repeats on a 400-year cycle, so a birth weekday is fully determined by the date — no lookup table required. The calculator derives it directly.

A related quirk worth knowing: your birthday usually moves forward one weekday each year, because 365 days is 52 weeks plus one day. It jumps two weekdays when a 29 February falls between the two birthdays. That is why the same date lands on a Monday, then Tuesday, then Wednesday, then skips to Friday.

Where exact age matters

• School admissions — cut-offs are usually set at an age on a specific date, not today.
• Visas and passports — child and adult fees often turn on age at the date of travel or application.
• Pensions and benefits — entitlement dates are calculated to the day.
• Medical dosing — paediatric doses can depend on age in months.

Set the "age on" field to the relevant date rather than measuring to today. For the gap between two people, use the age difference calculator; for your age on the Islamic calendar, the Hijri age calculator.

Chronological age calculator for tests and reports

Your chronological age is simply the time since you were born. Nothing more. It is the figure this calculator gives you, and it is the one schools, clinics and test publishers ask for.

Psychologists and teachers write it in a special short form: years;months. A child of 7 years and 4 months is written 7;4. Standardised tests — including the reading, IQ and speech assessments sold by publishers such as Pearson — compare a child's raw score with children of the same chronological age. Get the age wrong by one month and you can pick the wrong scoring table.

1. Enter the date of birth.
2. Set Age as at to the test date, not today's date.
3. Read off the years and months. Note the leftover days too.

Rounding rules differ. Some test manuals round up to the next month when the leftover days are 15 or more. Others never round. Always follow the manual for the test you are scoring.

How many months old am I?

Multiply your whole years by 12, then add the extra months. The Total months line in the result does this for you. Parents use it most for babies and toddlers, because doctors track growth in months until about age two.

Corrected age for premature babies

A baby born early has two ages. The chronological age counts from the birth date. The corrected age counts from the original due date. Doctors use corrected age to judge growth and milestones, usually until the child turns two.

Chronological age vs biological age

People often search for a biological age calculator or a "real age" test. These are different tools. Biological age is an estimate of how old your body seems, built from things like blood pressure, fitness or DNA markers. No one can work it out from a birth date alone.

• Chronological age — exact, fixed, the same for everyone born that day. This page.
• Biological age — an estimate. It changes with health and lifestyle, and different methods disagree.

For legal, school and medical forms, chronological age is the one that counts. Want your age on the Islamic lunar calendar instead? Try the Hijri age calculator. Comparing two people? Use the age gap calculator.

Dog age calculator: dog years to human years

The old “multiply by 7” rule is wrong. Dogs grow up fast and then age more slowly. The American Veterinary Medical Association’s rough guide for a medium-sized dog:

• First year = about 15 human years.
• Second year adds about 9, so a 2-year-old dog is about 24.
• Each year after adds about 4 to 5 human years. Large and giant breeds age faster.

So a 5-year-old dog is about 36 in human years, and a 10-year-old dog about 56. Find your dog’s exact age here first, then convert it. For a full dog age chart by size, see the dog years to human years guide.

Other ways to use this calculator

The same exact-age maths answers many different questions.

• Online chronological age calculator — set “Age as at” to the test date to get years;months for school and psychology reports.
• Corrected age calculator for preemies — enter the original due date instead of the birth date to get a premature baby's corrected (adjusted) age.
• Newborn and pediatric age calculator — the total weeks and total days lines give a baby's age the way clinics record it.
• Pet age calculator — enter your dog's or cat's birthday for its exact age, then read our dog years chart.
• How old am I? — enter your date of birth and today’s date for your exact age.
• Age in days — the result also shows your total age in days, weeks, months and hours.
• Date of birth calculator — enter any date of birth and an “as at” date to get the age on that day.
• Real age calculator — this gives your real calendar age, not a health or “biological” estimate.

Related guides

• Dog Age Chart: Dog Years to Human Years

Frequently asked questions