Jenna is American. Tom is British. Married, both working remotely from wherever the WiFi and the visa rules allow. Their tax planning isn't twice as complicated as a same-nationality couple's — it interacts, which is worse. Here's how to actually structure it.

Why Two Passports Beat Two of the Same Problem

When both partners share a nationality and a residency plan, coordination is fairly linear: one tax system, one exit strategy, one set of rules to learn. Add a second nationality and each of the following stops being one problem and becomes two, tangled together: exit tax obligations, residency-establishment options, joint income structuring across two tax systems at once, cross-border estate planning, and, if it ever comes to that, divorce planning across two jurisdictions rather than one.

Jenna and Tom's situation is the most common version of this: one partner with citizenship-based tax obligations that follow them everywhere, one partner without.

Jenna's Side: The US-Involved Couple

As a US citizen, Jenna owes US tax on her worldwide income regardless of where she and Tom actually live — citizenship-based taxation (CBT) doesn't care about her passport-country address. Tom, as a UK citizen with no US ties, doesn't have that obligation at all.

That asymmetry is the whole game, and it shapes how they hold things. Common structuring for a couple like this: Tom holds the bulk of their joint investment assets, since assets held by the non-US spouse generally sit outside US tax; Tom structures any business ownership, since a non-US spouse's ownership stake can avoid triggering GILTI or Subpart F rules that would apply if Jenna held it; Jenna typically files married filing separately rather than jointly, since joint filing can pull Tom's non-US income into US reporting; and their estate plan is built specifically to minimize US estate tax exposure on Tom's side, since the ordinary US marital deduction doesn't apply when the surviving spouse isn't a US citizen.

One warning that catches couples like Jenna and Tom off guard: if Jenna's name is on any of Tom's non-US financial accounts, even a shared household account, that account can trigger FBAR and Form 8938 reporting obligations for both of them, not just for Jenna.

Tom's Side: The UK-Involved Couple

If Tom instead of Jenna were the one establishing UK residency, the exposure runs the other way. Before the UK's 2025 non-dom reform, a non-domiciled spouse resident in the UK could often shelter foreign income and gains from UK tax entirely — historically, this made a mixed-nationality couple basing themselves in the UK an attractive, couples-favoured structure. That door has largely closed for new arrivals. The current regime is residence-based and time-limited rather than domicile-based, which means what matters now isn't which spouse counts as "domiciled" but how long each of them has actually been UK tax resident, assessed under the UK's statutory residence tests.

The practical upshot for a couple like Jenna and Tom: if Tom becomes UK tax resident under those tests, which turn on day counts and specific ties rather than just where he says he lives, his UK tax exposure can extend to income and joint assets the couple think of as Jenna's, depending on how they're held. The old workaround of routing everything through the non-dom spouse no longer does the job it used to.

The Same Shape, an Australian Passport

Swap Tom's British passport for an Australian one and the mechanics change, but the underlying problem doesn't. Australian residency can create Australian tax implications for the non-Australian spouse under specific circumstances — shared homes and financial ties both count as evidence of residency, not just physical presence.

The sharper trap is CGT Event I1: when an Australian tax resident ceases to be one, Australia treats it as if they'd sold their worldwide capital assets on the day they left, crystallising a capital gain whether or not anything was actually sold. If those assets are jointly held with a non-Australian spouse, the Australian spouse can carry the full deemed-disposal tax bill on assets the couple think of as shared — while the non-Australian spouse's own share of the same asset isn't touched by Australian tax at all. It's a lopsided bill hiding inside what looks like joint ownership.

Structuring the Couple, Not Just the Individuals

Most mixed-nationality couples land on one of three approaches. One primary residency for both is the simplest: both establish tax residency in the same nomad-friendly jurisdiction (UAE, Cyprus, Panama and similar are common choices) while each still carries their own nationality-based obligations separately. Split residency is rarer and more complex: each spouse resident somewhere different, usually driven by a specific factor like family, business location or healthcare access, and it requires careful structuring to avoid the two systems clashing. Sequential structuring has one spouse establish residency first, with the other joining later, timed to optimise the combined tax outcome.

Estate Planning Needs Both Passports at the Table

Mixed-nationality estates aren't just bigger versions of single-nationality ones; they're genuinely different. Each spouse's nationality can trigger its own estate tax rules independent of where they lived. The US marital deduction, which lets a surviving US-citizen spouse inherit tax-free, simply doesn't apply if the surviving spouse isn't a US citizen. Tom would need a Qualified Domestic Trust (QDOT) structure to get anything like the same treatment. Different jurisdictions apply different succession rules on top of that, and property scattered across countries adds real practical friction on top of the legal complexity. This is not a do-it-yourself corner of the plan.

What Happens to the Kids

A child born to Jenna and Tom would likely hold both US and UK citizenship from birth, and that comes with a lifetime, not a childhood, of consequences. Each citizenship carries its own future tax obligations — in the US case, obligations that follow the child for life unless formally renounced, and renunciation is easier for some nationalities than others. Schooling and healthcare choices interact with citizenship status too, and long-term financial planning for the child needs to account for citizenship-based obligations that won't fully show up until they're adults filing their own returns.

Where to Start

Get joint cross-border advice from one adviser who sees both sides, not two advisers who each only see their own country. Choose one primary residency jurisdiction where possible. Structure asset ownership deliberately, the way Jenna and Tom did with Tom holding the joint investments. Build the estate plan around both nationalities from day one. Then review it regularly — the UK's 2025 reform is proof that the ground under couples like this can move.

Start With One Conversation

Different passports, one household? Tell us both nationalities and we'll tell you the one planning decision, residency, estate, or business ownership, that actually needs to happen first.

This is general information for a fact pattern that varies enormously by couple — nothing here substitutes for advice from a qualified cross-border adviser who has seen your actual documents.