Why Counting Days could not Save You: The US–Spain Tax Reality Most Americans Miss

For many Americans living between Spain and USA, tax planning starts with the wrong question.

“How many days can I stay without becoming tax resident?”

It sounds reasonable. It works —more or less— in many countries.

For US citizens, it is usually the beginning of the problem.

The reality is uncomfortable but simple: the United States and Spain are not even playing the same game when it comes to tax residence. And trying to apply European-style day-count logic to a US passport often creates more exposure, not less.

The US System: You Don’t Opt Out

Most tax systems begin with residence.
The US begins with citizenship.

If you are a US citizen or a green card holder, the IRS does not ask where you live. It assumes worldwide taxation as the default position. Residence planning may affect how you are taxed, but not whether you file.

That is why:

• You must file a US tax return every year, even if you live permanently in Spain

• Spanish income is still US-reportable

• “I don’t owe anything” does not mean “I don’t have to file”

This is not a loophole. It is the backbone of the US system.

Many Americans only discover this after years abroad, when penalties—not tax—become the real issue.

Spain’s Perspective: Presence Plus Reality

Spain comes at the issue from the opposite direction.

Spanish tax residence is built around presence and substance, not nationality. If you spend more than 183 days in Spain during the calendar year, Spain considers you resident. Simple on paper, less so in practice.

Unlike the US:

• Any physical presence counts as a full day

• Arrival and departure days are included

• Short trips abroad usually do not break residence

• The burden of proof is on the taxpayer, not the tax authority

And crucially, Spain is not impressed by technical compliance that ignores economic reality.

Why the 183-Day Rule Is Not a Safety Net

Many American clients assume that staying under 183 days keeps them “safe.”
In Spain, that assumption is fragile.

Even without hitting the day threshold, Spain can treat you as resident if your centre of economic interests is located there. This often affects Americans who:

• Work remotely from Spain

• Run US businesses while living here

• Are digital nomads or autónomos

• Exercise management or control functions from Spain

In other words, you can count days perfectly and still lose the residence argument.

Double Taxation Isn’t the Risk. Double Confusion Is.

The US–Spain tax treaty exists, but it does not eliminate filing obligations. It coordinates them.

In practice, this means:

• Spain taxes first if you are resident

• The US taxes second through reporting, with relief via credits or exclusions

• Timing mismatches between tax years create complexity

• Not all income categories align cleanly between systems

Most problems arise not from paying tax twice, but from reporting the same income differently in two jurisdictions.

That inconsistency is what triggers audits.

The Myth of Being “Tax Resident Nowhere”

Some mobility strategies aim for deliberate ambiguity: not quite resident in Spain, no longer resident in the US. “in practice,” floating in between.

For Americans, this is a high-risk position.

• The US taxes you regardless

• Spain may assert residence by presumption or economic substance

• Treaty protections rely on actual residence, not avoidance of it

Trying to disappear between systems usually means losing the protections of both.

Two Logics, One Necessary Conclusion

Spain asks whether your life is here.
The US asks whether you belong to it.

Neither system cares much about the internal logic of the other.

For Americans in Spain, the goal is not to escape US taxation. That is rarely realistic. The real objective is to build a clear, defensible position that works on both sides at the same time.

That means aligning Spanish residence, US filings, treaty positions, and information reporting into a single coherent strategy.

Before You File

If you are an American living in Spain, your tax situation is not “foreign.” It is binational by default.

Getting it right requires more than counting days. It requires understanding which system is actually in control—and when.

At American&Legal Spain, we help US clients structure their residence and filings so that what makes sense in Spain does not create problems in the United States, and vice versa.

Before you file—on either side—make sure your position is not just compliant, but credible.