Age on Other Planets Calculator

How Planet Ages Are Calculated

1. Count the days from your birth to the date you choose: 13,349 days from June 15, 1990 to January 1, 2027.
2. Divide by the planet’s year in Earth days. Mars: 13,349 ÷ 686.972 = 19.43 Mars years.
3. For the next birthday, take the next whole number (20), multiply by the planet’s year (20 × 686.972 = 13,739.4 days) and count that many days from your birth date: January 26, 2028.

A planet’s year is the time it takes to go once around the Sun. The farther out a planet is, the longer its path and the slower it moves, so outer-planet years are long and inner-planet years short.

Planet Years and the Default Example

Venus is the odd one: it spins so slowly (once every 5,832.5 hours, about 243 Earth days, per NASA) that one turn takes longer than its 224.7-day year, and its sunrise-to-sunrise day of 2,802 hours (about 117 Earth days) means a Venus year holds fewer than two sunrises. Neptune has completed only one orbit since its discovery in 1846, and nobody alive has had a first Uranus, Neptune or Pluto birthday.

Ages at Familiar Earth Birthdays

Where the Numbers Come From

NASA’s Planetary Fact Sheet lists each planet’s orbital period in Earth days. The calculator uses the same periods to three decimals from NASA’s individual planet fact sheets, measured equinox to equinox (the tropical year, which is what “a year” means on Earth: 365.242 days). Pluto, now classed as a dwarf planet, uses its orbit relative to the stars (90,560 days) because NASA notes its equinox-to-equinox period is not well known.

Common Mistakes and Small Differences

• Multiplying instead of dividing. A Mars year is 1.88 Earth years, so your Mars age is your Earth age ÷ 1.88, not × 1.88. Planets with longer years make you younger.
• Which year. Measured against the stars instead of the equinoxes, Uranus years are about three months longer (30,685 days) and Neptune years about a year longer (60,189 days), which moves those birthdays later.
• Time of birth and time zone. The calculator treats birth as midnight; a birthday on another planet can fall a day earlier or later depending on the hour you were born.
• Planets do not move at a constant speed. Orbits are slightly oval, but a year is still one full orbit, so ages and birthdays are not affected.

What This Calculator Does Not Cover

It does not convert days (a Mars solar day, or sol, is 24.7 hours) or count birthdays by local calendars that future settlers might use, such as the Darian calendar proposed for Mars. Your weight on each planet is on the companion weight calculator.

Frequently Asked Questions

How to Use This Calculator

1. Enter your birth date — the day you were born.
2. Set the age-on date — today, or any date you want to check.
3. Pick a planet to feature — it appears in the headline; every planet is listed below it.
4. Read your ages and birthdays — your age in each planet’s years and the calendar date of your next birthday there.