Age on Other Planets Calculator

Age on other planets: how old you are in Martian, Jovian and Mercurian years

Enter your date of birth and this age on other planets calculator converts your age into the years of every planet, from Mercury’s quick 88-day loop to Pluto’s 248-year orbit. It also works out the date of your next birthday on each world — the day a whole number of that planet’s years will have passed since you were born — and how many days away it is.

The calculation is honest and simple: your age in days on Earth divided by the length of each planet’s year in Earth days, using the sidereal orbital periods from NASA’s Planetary Fact Sheet. It is a favourite classroom exercise and a quick way to feel the scale of the solar system: a 30-year-old has seen 124 Mercury years but has not yet had a first birthday on Saturn. The page runs entirely in your browser.

How to use the Age on Other Planets

1. Enter your Date of birth. The Age as of field starts at today’s date; change it to see your age on any other date.
2. Choose a planet in Highlight, or click a row in the table, to show it in the big panel with your next birthday there.
3. Read your Earth age and days lived in the small tiles, then the full table: year length, your age, the date of your next birthday and how many days until it.
4. Use the copy icon on a row to copy that age, for example “13.8 Mars years”, into a message or a worksheet.

Age on Other Planets features

How the calculation works

A planet’s year is the time it takes to complete one orbit of the Sun. Kepler’s third law ties that period to the orbit’s size — the period squared is proportional to the distance cubed — so the farther out a planet is, the much longer its year. The calculator counts the whole days between your birth date and the reference date, then divides by each planet’s sidereal period: age on Mars = days lived ÷ 686.980. Your next birthday there is your birth date plus the next whole multiple of that period, rounded up to a calendar day.

The sidereal period is measured against the fixed stars. Earth’s is 365.256 days, slightly longer than the 365.242-day tropical year our calendar follows, so a “birthday” here lands within a day of your calendar birthday but is not identical to it. The age calculator handles the calendar version with years, months and days.

Year lengths across the solar system

Nobody alive has had a Neptune or Pluto birthday, and only people over 84 have had a Uranus one. A Saturn first birthday arrives at 29 years 5 months — a nice milestone to plan with the countdown timer.

Years versus days: the other half of the story

Age in planetary years says nothing about how many sunrises you would have seen. Mars rotates almost like Earth (a sol is 24 h 39 m), so a Martian year contains 668.6 sols. Venus rotates so slowly, and backwards, that its solar day of 117 Earth days gives fewer than two sunrises per Venusian year; Mercury manages just half a sunrise per year, because its 176-day solar day is exactly twice its year. Jupiter, in contrast, spins in under ten hours and packs more than 10 000 days into each of its years. The weight on other planets calculator answers the companion question of what the scales would show when you got there.