I got a €47,000 tax bill because I miscounted by one day.

In late 2024 I was living the dream — Lisbon in spring, Mexico City in summer, Barcelona for the autumn. I'd been a "digital nomad" for four years and had it figured out. Or so I thought.

In April 2025, a registered letter arrived at my mom's address in Seoul. The Spanish tax authority claimed I had spent 184 days in Spain in 2024 and was therefore tax-resident on my worldwide income. The bill, with penalties, came to €47,210.

I sat on the floor of a coworking space in Bali and counted, one boarding pass at a time. They were right. I had spent 184 days. I'd missed the line by one. single. day.

Why this happens to almost everyone

I started asking around. Out of my 30 closest nomad friends, 11 had a version of the same story. Some were lucky — a treaty saved them. Some, like me, paid. Most still had no clue they were at risk.

The tools we were using were laughable. A Google Sheet. An iPhone reminder. A Telegram group where we asked each other "wait, does Schengen include Croatia now?". We were running six-figure-income lives on stationery from 1998.

I'm an engineer. I built fraud infrastructure at fintech companies for eight years. So I did what engineers do when their tool sucks — I built a better one. For myself first. Then for those 30 friends. Then it leaked.

What NomadOS actually does

NomadOS is the operating system I wish I'd had in 2024. It quietly counts your days across 47 jurisdictions — using your calendar, your boarding passes, your phone's location if you let it — and tells you, weeks in advance, when you're about to cross a line you can't uncross.

It also tells you what to do about it. Move to Croatia for 12 days and save $18K. Apply for Portugal NHR before December 31. Book a flight out of Spain on Sunday or owe €47,000 on Monday.

That's it. No Big-Four jargon, no $400/hour partner calls. Just — here's where you are, here's where the cliff is, here's how to walk around it.

Why I'm doing this in the open

I'm a solo founder. I work out of cafés, planes, and my friend Lina's spare room in Porto. There is no marketing department. There is no investor deck. There's just this product, the people who use it, and the fact that I lost €47,210 to one day of bad arithmetic and refuse to let that happen to anyone else who reads this far.

If you're a nomad, a remote founder, an EU-passport holder spending suspicious amounts of time in the wrong countries — please run the free residency scan. Even if you never sign up. Even if you ignore everything else here. Just count your days.

That's the entire point.