Can the tax authority know how many days I spend in Spain?

Short answer: yes, much better than you think. The Spanish tax agency (AEAT) doesn't have a camera at every border, but it doesn't need one: your daily life leaves a trail of dated, located data, and a good part of that trail is reachable in an audit. Understanding what they can see is the first step to avoiding surprises — and to preparing your own version with better evidence.

The classic sources

• Card movements and cash withdrawals. The star source. Every in-person payment is a point on the map with date and time. A continuous series of payments in Madrid supermarkets and cafés is very hard to argue with.
• Banking and intermediary data. Banks report balances, movements and ownership. Automatic exchange of information between countries (CRS) means your foreign accounts surface too.
• Municipal registration, property records and utilities. Where you're registered, which homes are in your name and what they consume: an "empty" home with normal electricity and water usage tells a story.
• Road tolls, traffic cameras and parking. Your car testifies too: plates read on motorways and regulated zones place the vehicle — and, unless proven otherwise, its usual driver.

The fastest-growing sources

• Flight and border data. Airlines report passenger data (PNR/API) and the European entry/exit system records external EU border crossings by non-EU nationals. Inside Schengen there are no stamps, but your boardings live in databases.
• Phone networks and roaming. Which network your phone connects to, and from which country, is data that exists and can end up in a case file with the appropriate order.
• Your own public footprint. Social media, interviews, professional profiles with "based in…": everything you publish is usable. Cases have been reinforced with Instagram stories.

How they use it: the presence narrative

A residency audit doesn't try to prove your 365 days one by one. It builds a presence narrative from the available indicators — "your usage, payments and movements are those of a person living in Spain" — and hands it to you. From there, the burden of dismantling it is yours, day by day and with documents. If your only answer is "I was abroad, trust me", you lose.

What this means for you

The lesson isn't to hide — the trail exists anyway — but to play the same game with better cards: know exactly how many days you have in each country and have every stay documented before anyone asks. It's the difference between answering a notice in a week with a tidy report, or spending six months hunting boarding passes from three years ago.

That is exactly the work Daywhere does for you: it counts your days country by country with background GPS, stores dated proof of every stay and lets you export it all as a report when the letter arrives. And if you want to know where your year stands right now, start with the residency calculator.