How old are you on other planets?

Enter a date of birth to see the age on every planet in the solar system, and the Earth date of the next birthday on each one.

A year is one trip round the Sun

On Earth that takes 365 days and a quarter, which is why we add a leap day every four years. The other planets go round at their own pace: the closer to the Sun, the shorter the trip. Mercury, the closest, goes round in 88 days, so a ten-year-old on Earth is 41 on Mercury. Neptune, the farthest, takes almost 165 Earth years, so nobody has ever had a Neptune birthday.

What the numbers look like

  • Mercury: about four birthdays for every one on Earth. The fastest way to grow up.
  • Venus: a birthday every seven and a half months.
  • Mars: just under two Earth years per birthday, so a 30-year-old is about 16.
  • Jupiter: nearly twelve Earth years. Many people have only two or three Jupiter birthdays by 30.
  • Saturn: about 29½ Earth years. A first Saturn birthday comes at 29, a second at 59.
  • Uranus and Neptune: 84 and 165 Earth years. Most people never reach one.

Each result also shows the Earth date of the next birthday on that planet, worked out by adding whole planet years to the birth date. Some of those dates are close: a Mercury or Venus birthday is never more than a few months away.

A card for an out-of-this-world birthday

The age on Mars makes a good card for a space-mad child or an adult who would rather not say the Earth number out loud. The button under the result opens the card maker with a Mars birthday title and a message that mentions Mercury, ready to send as a link. Their next Mercury or Venus birthday is a fine excuse for a card on a day that isn’t their real birthday at all.

More birthday maths

The milestone calculator finds the day someone turns 10,000 days or a billion seconds old. The golden birthday calculator finds the year their age matches their birth date, and what day was I born tells them the weekday.

Common questions

How is the age on another planet worked out?

By dividing the number of days someone has lived by the length of that planet’s year in Earth days: 88 for Mercury, 687 for Mars, about 4,333 for Jupiter. The answer is how many times the planet has gone round the Sun since they were born.

Why use the planet’s year and not its day?

Age counts trips round the Sun, so a planet’s year is the fair comparison. Days are a different story: a day on Venus (243 Earth days) is longer than its year, and a day on Jupiter is under ten hours.

Where do the numbers come from?

The orbital periods in NASA’s planetary fact sheets: Mercury 87.97 days, Venus 224.70, Mars 686.98, Jupiter 4,332.59, Saturn 10,759.22, Uranus 30,688.5 and Neptune 60,182.

What about Pluto?

Pluto takes about 248 Earth years to go round once, so nobody alive has reached their first Pluto birthday. It has been classed as a dwarf planet since 2006, which is why it isn’t in the list.

Is anything I enter saved?

No. The maths runs in your browser. Nothing is sent anywhere and nothing is stored.