A tool about how arbitrary a year is
Your Age on Every Planet
A year is just one lap around the Sun — and everyone else laps at a different speed. Give your birthday and find out that you're a pensioner on Mercury, middle-aged on Mars, and still an infant on Neptune.
Enter your date of birth
Nothing is uploaded. Everything is worked out in your browser and forgotten the moment you leave.
About This Tool
Your age feels like a fact about you. It isn't — it's a fact about the Earth. All "thirty years old" really means is that the particular rock you live on has gone around the Sun thirty times since you showed up.
Stand somewhere else in the solar system and the number changes completely. Mercury laps the Sun every 88 days, so it hands out birthdays four times a year. Neptune takes 165 Earth years for a single lap, which means no human being who has ever lived has celebrated even one Neptunian birthday.
How To Use It
- Enter your date of birth. That's the only input, and it never leaves your device.
- Read your age on each of the eight planets, calculated from each one's real orbital period.
- Check the date of your next birthday on each world — on Mercury it's probably in the next few weeks.
- Look at the number of local days you've experienced too. It rarely matches your intuition, and on Venus it barely makes sense at all.
Why This Exists
Because it quietly dismantles something we treat as fixed. A "year" is not a unit of time handed down by the universe; it's a local accident of orbital distance. Somewhere out past Jupiter, everything you've done in your life happened in a couple of years.
It's also the fastest way to feel the actual size of the solar system. Not in kilometres, which mean nothing to most of us, but in birthdays — which mean quite a lot.
Frequently Asked Questions
How is my age on another planet calculated?
A year is simply one trip around the Sun, and every planet takes a different amount of time to make that trip. The tool counts how many Earth days you have been alive and divides by the length of each planet's year, so your age on Mars is your age in Earth days divided by the 687 days Mars takes to orbit.
Why am I so much older on Mercury?
Mercury is closest to the Sun and races around it in just 88 Earth days, so it packs more than four Mercury years into every Earth year. If you are 30 on Earth, you are about 124 on Mercury.
Can I ever have a birthday on Neptune?
Almost certainly not. Neptune takes about 165 Earth years to orbit the Sun once, so you would need to live to 165 to celebrate your first Neptunian birthday. Nobody has ever come close.
Why is a day on Venus longer than its year?
Venus spins on its axis extraordinarily slowly and in the opposite direction to most planets. One rotation takes longer than one orbit, which means a Venusian year contains fewer than two of its own days. Mercury is strange too, with a single sunrise-to-sunrise day lasting about twice its year.
Is my birthday stored or sent anywhere?
No. Everything is calculated in your own browser. Your date of birth is never uploaded, never stored, and never shared with anyone.
Does it work on mobile?
Yes. It works on any modern mobile browser, including Chrome, Safari, and Firefox. Enter your date of birth and all eight planets appear straight away.
More Games & Tools You'll Love
The Distance You've Traveled →
You've never been still. See how far Earth's spin and the galaxy have carried you since birth.
Browse Everything →
The full catalog of nostalgic, weird, and mind-bending single-purpose browser toys and games.