Dual Tax Residency Explained: Why Moving Abroad Doesn’t Always End Your Tax Residency

When a move abroad doesn’t create a clean break

Consider a British expat who moves to Portugal, rents a home in Lisbon, and registers locally. She still keeps a small flat in London, returns regularly to see family, and remains a director of her former UK company.

As far as she is concerned, the move is complete. Her day-to-day life is now in Portugal.

But from a tax perspective, the picture may look very different. If the UK still sees enough ongoing ties under its tax residence rules, and Portugal also treats her as resident under its own domestic rules, she may find herself caught between two systems at once. HMRC’s guidance on the Statutory Residence Test makes clear that UK residence is not based on day count alone, while Portugal’s tax residency rules show that residence can also depend on factors such as time spent in the country and whether a home is maintained there.

What looked like a straightforward relocation can quickly become a cross-border tax problem.

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What dual tax residency means

Dual tax residency happens when more than one country treats you as a resident for tax purposes under its domestic rules.

That can happen because each country uses its own test. One may focus heavily on day counts. Another may look at where your personal and economic ties are strongest, where your family lives, or where your work and business activities are centred. During a relocation, or in periods when life is spread across borders, those tests can easily overlap.

When that happens, both countries may assert residence-based tax and reporting obligations. In some cases, relief may be available through a tax treaty, but that does not make the issue automatic or stress-free. The compliance burden can still be significant. The purpose of double taxation conventions is to reduce the risk of the same income or gains being taxed twice, but they do not eliminate the need to analyse the facts carefully.

Why it happens more often than people think

Many expats think tax residency is mainly about where they spend most of their time. Time matters, but it is rarely the whole story.

A person may move abroad while still keeping important links to their previous country, such as:

• a home kept for visits or future use
• a spouse or children who remain there for part of the year
• regular return trips for work or family reasons
• ongoing business involvement, including directorships
• local bank accounts, memberships, healthcare registration, or other signs of continuing attachment

That is why tax residence often changes more slowly than lifestyle does. You may feel that you have moved, while the facts still suggest an ongoing connection to your former country.

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Common signs you may still be tax resident in your former country

If you have relocated, these are some of the most common warning signs that your old country may still have a claim:

You still have a home there.

Even if you mainly live abroad, a property that remains available for your use can matter. HMRC’s guidance specifically treats the availability and use of a home as relevant in residence analysis, and Portugal’s tax authority also refers to maintaining a dwelling in circumstances suggesting an intention to keep and occupy it as a habitual residence.

Your family is still based there.

If a spouse, partner, or children remain in your former country, that can be an important factor.

You return regularly.

Short visits for birthdays, meetings, holidays, or school events can add up more quickly than expected.

You still work there in some form.

That might mean employment, client work, board meetings, or managing a business from afar.

Your old ties were never fully unwound.

Deregistering late, keeping healthcare or local registrations active, or maintaining too many practical links can weaken the argument that you truly left.

None of these points automatically means you are a dual resident. But if several apply at once, it is worth reviewing your position carefully.

What tax treaties can and cannot do

Many countries have double tax treaties designed to reduce the risk of the same person being treated as resident in both places for treaty purposes.

These treaties often contain so-called tie-breaker rules. In simplified terms, they look at questions such as:

• Where do you have a permanent home?
• Where are your closest personal and economic ties?
• Where do you usually live?
• If it is still unclear, what is your nationality?

The aim is to allocate residence to one country for treaty purposes. But that does not mean the issue disappears overnight.

First, treaty analysis depends heavily on facts. Second, you may still have filing or disclosure obligations in the other country, even if the treaty helps determine residence. And third, not every case is clear-cut. If your life is genuinely spread across two places, proving which one is your real centre of life can be difficult.

Why records matter more than most expats realise

In practice, tax residency disputes often come down to evidence. What matters is not only where you intended to live, but what your records show. If a tax authority reviews your position later, it will usually want facts, dates, and documentation rather than general explanations. Useful records may include:

• travel history and day counts
• flight confirmations and itineraries
• lease agreements, utility bills, or proof of accommodation
• meeting records and work calendars showing where duties were carried out
• school records or other evidence showing where family life was based
• supporting documents showing where financial and practical life was centred

This matters because tax authorities increasingly compare information across borders. If your filings say one thing but your travel pattern, work activity, or accommodation records suggest another, that inconsistency can create problems.

Practical steps expats should take

A move abroad is easier to manage from a tax perspective when it is planned early and documented properly. A few practical steps can make a big difference.

Check the rules in both countries.

Do not rely on assumptions. Review the domestic residency rules of the country you are leaving and the one you are moving to.

Plan the exit before the move.

Where possible, deal with open issues in advance. That might include housing, directorships, employment arrangements, or family logistics.

Track travel carefully.

Even short trips can matter, and counting rules vary from country to country. Good travel records are one of the simplest ways to reduce future uncertainty.

Keep your paperwork consistent.

Your immigration, tax, employment, and practical life records should support the same overall story.

Reassess every year.

Residency is not something to check once and forget. Work patterns, family arrangements, and travel habits can all change.

A practical way to stay organised

Because tax residency questions often depend on factual evidence, many expats now rely on dedicated tracking tools to keep their records in order.

Platforms such as Flamingo Compliance help internationally mobile users track travel days across countries, monitor potential tax residency and visa threshold exposure, and maintain structured records for adviser review. They can also support a cleaner exit from a previous residency position by helping users organise the evidence needed to show that tax residency in one country ended before another began, reducing the risk of being treated as resident in both. That does not replace professional advice, but it can make it much easier to understand your position and respond if questions arise later.

For expats juggling multiple countries, trips, and reporting obligations, staying organised is often half the battle.

The bottom line

Dual tax residency is not a rare technical problem. It is a common risk in modern expat life, especially when a move happens gradually or important ties to the previous country remain in place. Tax authorities and treaty frameworks make clear that residence can depend on a mix of presence, ties, and factual evidence rather than a simple change of address.

The key point is simple: moving abroad does not always end tax residency where you came from. In many cases, that needs to be demonstrated through facts, planning, and records.

For expats, the safest assumption is not that a relocation automatically resets everything, but that tax residence may need to be reviewed carefully on both sides of the move.