How far is worth it? The travel maths behind every pick

A forecast map can tell you where the sun is. It can’t tell you whether going there is worth it. Ticino might have nine hours of sun, but if you live in Basel and it’s 10:00, most of that sun happens while you’re on the train.

That’s the core of FOMO Sun: it compares the sun you’d get after travelling with the sun you’d get by staying home. Here is how.

1. Only the sun after you arrive counts

For today, the app looks at the forecast hour by hour and starts counting when you’d arrive. Leave at 10:00 on a 90-minute trip and the place’s morning sun doesn’t count; you’d have been on the train. Home is counted from now. Both sides end at sunset.

This alone removes most bad ideas. A place with two more hours of sun than home, three hours away, often comes out behind.

2. A small penalty for the trip itself

Travel isn’t free even when the sun is: tickets, effort, the trip back. On top of the lost hours, each trip takes a small fixed amount off, by length:

• under 1 hour: nothing
• 1 hour to 1.5 hours: 5 min
• 1.5 to 2 hours: 10 min
• 2 to 3 hours: 15 min
• 3 to 4 hours: 20 min
• 4 to 5 hours: 25 min
• 5 hours or more: 30 min

The numbers are small on purpose. They decide close races (two places with the same sun, one an hour further) without overruling a really sunny day.

3. It has to be clearly better than home

The result is called net sun. A place only counts as a sunny escape when its net sun beats home’s by at least 10 %. A few minutes more sun isn’t worth a train ticket, and forecasts aren’t that precise anyway.

When nothing clears that bar, the app says so: “Nothing in this range beats Basel right now. Enjoy it at home.” That answer matters as much as the others.

4. Train or car, whichever is faster

Every place has a train time and a car time from each home city. The app uses the faster one unless you pick a mode. Train times come from the Swiss public transport planner, including the last part: Rigi Kulm from Zurich isn’t 40 minutes just because Arth-Goldau is; the cogwheel railway counts too.

5. You choose the window

The travel window is yours: up to 30 minutes, an hour, two, or a long day trip. Inside it, the best net sun wins. Outside it, the app may still tell you if something far away is dramatically better, but it won’t pretend it’s close.

Why not just rank by sunshine?

Because the sunniest place is almost always far away, high up, or across a border. Ranking by raw sunshine would recommend the Engadin every day. Net sun recommends what is actually worth doing from where you are, today.

What I learned

The interesting number is a difference. Not “how sunny is it there” but “how much more sun do I get by going”.

Small penalties, clear thresholds. They’re easy to explain and hard to game, and when the answer is “stay home”, people trust the other answers more.