This site asks one question and answers it with real orbital mechanics. Here is what happens between the button and the answer.
Two stations count
There are two crewed space stations in this calculation: the ISS and China’s Tiangong. The ISS orbits at an inclination of 51.6° and sits about 420 km up. Tiangong is tilted 41.5° and sits about 390 km up, and has been permanently crewed since June 2022. So when this site says someone is above you, it means someone aboard one of those two.
What “above you” means
Not literally overhead. That would be a once-in-a-lifetime pixel. At any moment there is a spot on Earth directly below each station. This site counts a station as above you when you are within 500 km of that spot. From where you stand, that puts the station at least 37° above the horizon — well up the sky, not down in the haze. The 500 km is a choice. Stricter and you would almost never get a yes. Looser and “above you” stops meaning anything.
How the answer is calculated
Your browser asks for your location, then works out where both stations are right now using SGP4 — the standard orbital model — and the same orbital data NASA and the military use. It measures how far you are from the spot below each station, and compares that with the 500 km line. The distance on your screen is something else: the real straight-line distance to the crew, diagonally through the air. Not the altitude. At the very edge of the zone it is about 670 km, even though the station is only 420 km up.
Your location stays with you
Your location never leaves your device. It is not sent anywhere and it is not stored. All the maths happens in your own browser. The orbital data comes from USSPACECOM via Space-Track.org, and is refreshed once a day.
Why is the answer usually no?
Because the stations circle the whole planet and you are one small spot on it. Most of the time they are somewhere over an ocean nobody is standing in. Which is rather the point. If the answer were usually yes, it would not be worth asking.
Some places never get a yes
Above roughly 56° north or south, neither station ever passes directly overhead — the orbits simply do not reach that far. That rules out northern Scotland, most of Scandinavia, much of Canada and all of Alaska. You can still see a station from there: low in the sky, off towards the equator. It just never comes over the top.
Can both be above you at once?
Yes, and it is worth noticing when it happens. For any given spot on Earth, both stations are overhead together for only a couple of minutes per year.
Can you actually see it?
Only around dusk or dawn, when the sky above you is dark but the station is still catching sunlight. The rest of the time it is up there and invisible. So a yes here means a station is in the zone above you. Whether you can see it is a separate question of light, cloud and luck.
Does someone have to be aboard?
This site assumes someone is. Orbital data tells you where a station is; it says nothing about who is inside it. Both have been permanently crewed for years, so it is a safe assumption. But strictly speaking, the orbit is measurable and the passenger list is not.
