About the Age on Other Planets Calculator
This age on other planets calculator converts your age into the “years” of every planet in the solar system. A year is one trip around the Sun, and each planet takes a different time: Mercury races around in 88 days while Neptune needs almost 165 Earth years. Enter your date of birth and the date to measure to, pick a planet to highlight, and you will see your age on every world plus the date of your next birthday on the chosen planet.
It is a fun way to teach orbital periods and Kepler’s laws in class, a party trick for birthdays, and a neat way to plan a “Mars birthday” celebration. The chart compares your age across the planets, and the notes show how many days you have been alive.
Ages use each planet’s sidereal orbital period from the NASA fact sheets, measured in Earth days. Your Earth age here is in sidereal years of 365.256 days, so it can differ from your calendar age by a fraction of a day per year.
With the default inputs, the age on selected planet is 19.3 years. Change any value above to recalculate instantly.
How to use the age on other planets calculator
- 1Enter your date of birth.
- 2Set the date you want to measure your age on (for example today).
- 3Choose a planet to highlight.
- 4Read your age in that planet’s years and the date of your next birthday there.
- 5Compare your age on every planet in the chart and table.
Formula and method
A planet’s year is the time it takes to orbit the Sun once — its sidereal orbital period. The calculator counts the exact number of days between your birth date and the chosen date, then divides by each planet’s period in Earth days: 87.969 for Mercury, 224.701 for Venus, 365.256 for Earth, 686.980 for Mars, 4,332.589 for Jupiter, 10,755.699 for Saturn, 30,685.4 for Uranus, 60,189.018 for Neptune and 90,560 for Pluto.
Your next birthday on the selected planet is your birth date plus the next whole multiple of that planet’s period, rounded to the nearest day. Periods come from the NASA NSSDCA planetary fact sheets. Outer planets move more slowly because, by Kepler’s third law, the square of the period grows with the cube of the orbit size.
- days alive
- Calendar days from date of birth to the chosen date
- P
- Sidereal orbital period of the planet, in Earth days
Worked examples
Born 15 June 1990, age on Mars on 1 October 2026
There are 13,257 days between the two dates. Dividing by Mars’s 686.98-day year gives 19.30 Mars years. The 20th Mars birthday comes at 20 × 686.98 ≈ 13,740 days after birth — 27 January 2028.
Born 1 January 2000, highlighting Mercury
9,770 days ÷ 87.969 days ≈ 111.06 Mercury years. The 112th Mercury birthday is at 112 × 87.969 ≈ 9,853 days, on 23 December 2026. This person has not yet finished one Saturn year.
Born 10 March 1960, highlighting Jupiter
24,311 days ÷ 4,332.589 days ≈ 5.61 Jupiter years. The sixth Jupiter birthday arrives about 26,000 days after birth, on 13 May 2031.
Frequently asked questions
How old would I be on Mars?+
Divide your age in days by 686.98, the length of a Mars year in Earth days. A Mars year is about 1.88 Earth years, so a 30-year-old is roughly 16 in Mars years.
Which planet has the shortest year?+
Mercury, which orbits the Sun every 87.97 Earth days. A 10-year-old on Earth would be about 41.5 in Mercury years. Neptune has the longest planetary year at about 164.8 Earth years.
Why are years longer on outer planets?+
Outer planets travel a much bigger circle and move more slowly because the Sun’s gravity is weaker far away. Kepler’s third law says the orbital period squared is proportional to the average distance cubed.
Is a planet’s year the same as its day?+
No. A year is one orbit around the Sun; a day is one spin on the planet’s axis. Venus is unusual: its day (243 Earth days) is longer than its year (224.7 Earth days).
Why does my Earth age differ slightly from my calendar age?+
This calculator uses Earth’s sidereal year of 365.256 days for consistency with the other planets, while calendar years average 365.2425 days. The difference is about 20 minutes per year, so it rarely matters.