What a trip costs

It's our own estimate, worked out by our engine. It starts from what living costs in each destination —a TripPlan editorial figure— and adjusts it to how you travel, how many of you there are and how many days. No figure comes from an artificial intelligence: they are all worked out with the same formula, which is what lets two people get the same answer.

These are not live market prices. We don't check airlines or hotels, and we don't sell anything. The point isn't getting the euro right: it's knowing, before you go looking at prices, whether a trip fits what you have.

The flight is what varies most. It's estimated by distance from Spain and bought with reasonable notice. If you already have it, untick the box and you'll see the on-the-ground spending only.

This calculator tells you what it might cost before you leave. Keeping track once you're travelling is another thing: noting down the dinner, the taxi or the museum ticket and seeing, that same day, what you have left.

That's what My budget does, inside every TripPlan trip. You note an expense down in three taps, compare it with what you had planned per category, and it tells you how much you have left per day for the days remaining. If you go over, it tells you by how much: it never tells you off.

Your spending never leaves your phone. It's saved on the device itself, so noting things down works with no signal and no data — on a plane, on the metro, or in a country where you'd rather not spend on roaming.