A birthday every 687 days
Your birthday marks one more trip around the Sun with the Earth. Mars makes the same journey much more slowly: it is about one and a half times further from the Sun, travels more slowly in its orbit and has a longer path to cover, so one Martian year lasts 686.98 Earth days. If you counted your age on Mars, you would have a birthday roughly every 22 and a half months, and you would be only a little over half your Earth age.
The orbit picture shows the Sun at the centre, the Earth on the inner circle and Mars on the outer one. The faint marker on the Mars orbit is where the planet was on the day you were born. Every time Mars returns to that spot, you have a Mars birthday. The strip underneath lists them all, with the Earth age you were or will be on each one.
How we calculate it
We count the days since your birth and divide by 686.98, the length of a Martian year in Earth days, to get your Mars age. Each Mars birthday is your birth date plus a whole number of Martian years. Your age in sols is the time since your birth divided by the length of a sol, 88,775 seconds. The positions in the orbit picture come from the average speed of each planet around the Sun, measured from the standard starting point used by astronomers, 1 January 2000.
| Earth age | Mars age | Sols lived |
|---|---|---|
| 10 | 5.3 | 3,555 |
| 18 | 9.6 | 6,398 |
| 30 | 15.9 | 10,664 |
| 50 | 26.6 | 17,774 |
| 80 | 42.5 | 28,438 |
Worked example. Someone born on 12 April 1990 was 13,350 days old on 30 October 2026, which is 19.4 Martian years or about 12,993 sols. Their 19th Mars birthday was on 5 January 2026, when they were 35, and their 20th falls on 23 November 2027, when they will be 37.
Life on Mars time
Scientists who drive rovers on Mars live on sols for weeks at a time, shifting their working day by about 40 minutes every day to keep pace with the planet. A Martian year has its own seasons too, each roughly twice as long as ours, because Mars is tilted on its axis by about 25 degrees, similar to the Earth.
Questions people ask
How long is a year on Mars?
Mars takes 686.98 Earth days to go once around the Sun, about one year and ten and a half months. That is 668.6 Martian days, which are called sols.
What is a sol?
A sol is one day on Mars, the time it takes the planet to spin once relative to the Sun. It lasts 24 hours, 39 minutes and 35 seconds, so a Martian day is only a little longer than ours. Mission teams at NASA work on sols when they drive rovers.
Are the planet positions in the picture exact?
They are close but simplified. We use each planet’s average motion and draw the orbits as circles, which is accurate enough to show where Mars and the Earth are in their orbits, give or take a few degrees.
When is Mars easiest to see?
Around opposition, when the Earth passes between Mars and the Sun. That happens about every 26 months. The next one is on 19 February 2027, when Mars will be bright in the night sky all night long.
Sources. NASA Planetary Fact Sheet (orbital period 686.98 days; sol 88,775 seconds); mean orbital elements from JPL. Calculations run in your browser; nothing you enter is sent anywhere.