Age Calculator
Your exact age in years, months and days on any date you choose — with the countdown to your next birthday, the day of the week you were born, and how the same span looks in every other unit.
Instant answers
Works offline once loaded
Nothing you type is sent anywhere
Next-birthday countdown
Age on any date
Compare two people
Date of birth
Leave as today, or set a future or past date
Age
Next birthday
Days until—
Falls on—
Turning—
Half birthday—
The same span, every other way
| Unit | Total | Notes |
|---|
About the birth date
Day of the week—
Day of the year—
Leap year—
Star sign—
Chinese zodiac—
Generation—
Age on other planets
One year on a planet is one orbit of the Sun. A Mercury year takes 88 Earth days, so Mercury birthdays come round rather often.
Compare with someone else
Milestone birthdays
| Age | Date | Day | Status |
|---|
Instructions
How to use this calculator
Step by step
- Enter the date of birth. The three big numbers give the age the way it is normally said: so many years, months and days.
- Leave the "as at" date on today for a current age, or change it to work out how old someone was at a wedding, will be at a future event, or is on the day of an application deadline.
- The birthday panel shows how far through the current birthday year you are, how many days remain, what day of the week the next birthday falls on, and the exact half birthday.
- The units table converts the same span into everything from decimal years down to seconds, along with a few well-known approximations like heartbeats and full moons.
- The about panel covers the questions people usually ask next: what day of the week the birth fell on, whether it was a leap year, the star sign, and the generation.
- Enter a second birth date to see the gap between two people, both as a years-months-days figure and as a plain day count.
- If the date of birth is 29 February, choose whether birthdays in common years are counted on 28 February or 1 March — both conventions are in real use and they give different answers.
Good to know
- Age is counted in completed years. You are 29 right up to the moment of your 30th birthday, which is why the years figure here never rounds up.
- A leap-day birthday means the birthday exists only once every four years. Most legal systems treat the anniversary as falling on 1 March in common years, which is the default here.
- The months figure is calendar months, not thirty-day blocks. Two dates a month apart can be 28, 29, 30 or 31 days apart depending on where in the year they fall.
- For anything official — pensions, school entry, insurance, age of majority — check the exact wording, because some rules use "on or after the day before the birthday" and similar constructions that shift the boundary by a day.
- The planet ages use sidereal orbital periods, meaning one full orbit of the Sun. They are a fair conversion, not a joke: you really have been round the Sun that many times if you lived on Mars.
- The heartbeat and breath figures are illustrative averages, not measurements. Resting heart rate varies from about 50 to 90 beats a minute between healthy adults.
The maths behind it
- Age in years completed anniversaries of the birth date Never rounded up — the year increments on the birthday itself.
- Years, months, days borrow days from the previous month, then months from the year Calendar arithmetic, so month lengths are respected.
- Total days (as-at date − birth date) / 86,400,000 ms Computed on UTC midnights; leap days are included automatically.
- Decimal years total days / 365.2425 The mean Gregorian year length.
- Age on another planet Earth days lived / that planet's orbital period in Earth days Mercury 87.97 days, Neptune 60,182 days.
- Synodic month 29.530588 days New moon to new moon; used for the full-moon count.
Why does the age not go up on the day before my birthday?
Because you complete a year of life on the anniversary itself. Until that morning you have lived only part of the next year, and that part shows in the months and days columns. A few legal systems in East Asia count age differently, but the anniversary rule is the one used almost everywhere in the English-speaking world.
When do people born on 29 February have a birthday?
In leap years, on the day itself. In common years there is no such date, so a convention is needed. Most legal drafting treats the anniversary as 1 March, on the basis that a person turns older once the whole year has elapsed; many families celebrate on 28 February instead. Both options are on the page and they give a one-day difference.
How can I work out my age on a date in the past?
Change the "as at" date to that date. This is the quickest way to answer questions like how old someone was when a photograph was taken, or whether they were of age on a particular day.
Why is the months number sometimes not what I expect?
Calendar months vary in length, so the borrowing step uses the length of the month before the as-at date. Someone born on 31 January is, on 30 April, three months old with a few days deducted rather than three months exactly — the arithmetic is the same one that banks and courts use.
Are the generation labels official?
No. Generational boundaries are journalistic conventions rather than definitions, and different sources shift them by a few years in either direction. The ranges here follow the most widely cited set. Treat them as a conversation piece.
Does this account for time of birth or timezones?
No — it works in whole days, which is what every practical age question needs. If you were born late in the evening in one timezone and want the age reckoned in another, the answer can differ by a day, and you would need the exact birth time to resolve it.