MARSFEVER
Free instrument

MARSFEVER / TOOLS / AGE ON MARS

POSTAL AUTHORITY INSTRUMENT Nº 1

How old are you on Mars?

A Mars year lasts 687 Earth days — so your Martian age is roughly half your Earth age, and your Mars birthday only comes around every 22½ months. Enter your birthdate. We'll do the orbital mechanics.

You are — Mars years old.

Sols lived
—
Next Mars birthday
—
Which will be your
—
Earth age (boring)
—

Why your Mars age is smaller

Age is just laps around the Sun — and Mars takes longer laps. Sitting about 78 million kilometers farther out, Mars needs 686.98 Earth days to finish one orbit, nearly twice Earth's 365.25. Same you, same amount of living; the odometer just counts differently out there.

That has one delightful consequence: the Mars birthday. Every 687 days, you complete another Martian lap. Because they're rare, they land on a different season each time — a Mars birthday can drift from January to November over a decade. NASA mission teams genuinely celebrate spacecraft "landiversaries" in Mars years for exactly this reason.

The math, honestly

Mars age = your age in Earth days ÷ 686.98. Sols lived = your age in Earth days ÷ 1.02749 (a sol runs 24h 39m 35s, about 2.7% longer than an Earth day — see how long a day on Mars is). No rounding tricks, no timezone drama beyond your own browser's.

Got a kid with a Mars birthday coming up? Rusty the Rover writes letters from Mars — the first one's free, and a Mars-birthday transmission is exactly the kind of thing he'd take far too seriously.

Quick answers

How long is a year on Mars?
About 687 Earth days, or 669.6 sols — nearly twice an Earth year.
How do you calculate age on Mars?
Divide your age in Earth days by 686.98. A 30-year-old on Earth is about 15.9 in Mars years.
What is a sol?
A Martian day: 24 hours, 39 minutes, 35 seconds. Mars clocks run 2.7% slower against ours, which is why rover teams who live on "Mars time" slowly drift out of sync with Earth.
Would I actually age slower on Mars?
No — your body ages the same everywhere (relativity effects at planetary speeds are vanishingly small). Only the counting changes.

More instruments: your weight on Mars · Mars facts for kids