2026-02-21

How to Manage Joint Finances as a Mixed-Nationality Couple

When you and your partner hold different passports, every financial decision gets more complicated. Whose country do you bank in? Which currency do you use as your baseline? What happens to your investments when one of you is American and the other is not? How do you own property together across borders?

These are not hypothetical questions. Mixed-nationality couples deal with them constantly, and the answers have real tax, legal, and financial consequences. This guide walks through the major decisions and the tradeoffs involved.

Tax Residency Conflicts

The first thing to sort out is where each of you is tax resident, because that determines everything else — what you report, what you owe, and which tax treaties apply.

Most countries determine tax residency based on where you spend the majority of your time (the 183-day rule is common), where your permanent home is, or where your center of vital interests lies. But the rules vary by country, and it is entirely possible for two countries to both claim you as a tax resident simultaneously.

For couples, the complication multiplies. You and your partner might be tax resident in different countries, the same country, or (in complex situations) each claimed by two countries. The permutations affect joint filing options, tax treaty benefits, and how your combined income is taxed.

If you are both tax resident in the same country, your situation is simpler. You file according to that country’s rules (joint or separate, depending on what is available and optimal). Your investment and banking strategy can be unified.

If you are tax resident in different countries, you each file separately in your own jurisdiction. Combined financial planning becomes more complex because different tax rules apply to each partner’s income and assets. You cannot file a joint return across borders.

US citizenship adds a layer. The United States taxes its citizens on worldwide income regardless of where they live. If one partner is American and the other is not, the American partner has filing obligations to the IRS even if they live full-time in the Netherlands or Japan. This has knock-on effects on joint accounts, investment choices, and reporting requirements. See FATCA and CRS Explained for how this affects your banking.

Joint vs. Separate Accounts

The joint-or-separate question takes on extra weight when nationalities differ.

The Case for Separate Accounts

Regulatory clarity. When each partner’s money is in accounts clearly linked to their own tax residency, reporting is straightforward. Each person reports their own accounts, their own income, and their own gains. There is no ambiguity about whose money is whose.

FATCA protection. If one partner is American and the other is not, joint accounts create FATCA reporting obligations for the non-American partner’s bank. The bank now has a US person on the account and must report it to the IRS. Some banks will refuse to maintain a joint account with a US person at all. Keeping accounts separate avoids this friction entirely.

Estate and divorce simplicity. In the event of separation or death, clearly separated accounts with individual ownership make the legal situation cleaner. Cross-border estate and family law is complicated enough without commingled finances in multiple jurisdictions.

The Case for Joint Accounts

Practical spending. If you share daily expenses, a joint account for household spending avoids the awkwardness of one partner always paying and the other reimbursing. A shared Wise or Revolut account in your spending currency works well for this.

Transparency and trust. Some couples prefer full financial transparency. Separate accounts can feel like financial separation, which may not match the relationship.

Efficiency. Managing one household account is simpler than managing two sets of individual accounts plus transfers between them.

A Practical Hybrid

Many mixed-nationality couples land on a hybrid structure:

  1. Individual accounts for each partner in their respective “home” countries — these handle salary, tax-related transactions, and individual investments.
  2. A shared spending account (Wise or a local bank) funded by both partners for household expenses.
  3. Individual investment accounts — each partner invests through brokerages appropriate for their nationality and tax situation.

This preserves regulatory clarity while allowing practical shared spending. The key is documenting the structure and keeping it consistent.

Choosing a Base Currency

Every couple needs a currency they “think in” for budgeting and financial planning. For mixed-nationality couples, this is not always obvious.

Choose the currency you spend in. If you live in Portugal, your daily expenses are in EUR. That is your practical base currency regardless of whether one of you is British and the other is Australian.

Your base currency may change when you move. If you relocate from Portugal to Thailand, your spending currency shifts to THB. Your financial tracking should reflect this. Tools like FlashFi let you change your home currency and see your entire net worth recalculated accordingly.

Investments can stay in their original currencies. Your base currency is for tracking and reporting purposes. You do not need to convert all your investments into one currency. A British partner can hold ISA-eligible investments in GBP while an Australian partner holds super contributions in AUD. Your tracking tool converts everything to the base currency for a unified view.

For more on building a portfolio across currencies, see How to Build a Multi-Currency Investment Portfolio.

Investing When One Partner Is American

This is the single biggest financial complication for mixed-nationality couples where one partner holds US citizenship.

The PFIC Problem

US persons are subject to Passive Foreign Investment Company (PFIC) rules, which impose punitive taxation on non-US domiciled mutual funds and ETFs. This means the American partner should generally invest through US-domiciled funds (Vanguard, iShares US, Schwab), while the non-American partner may prefer European UCITS ETFs or local funds.

If you invest jointly — for example, through a joint brokerage account — the entire account is subject to US tax rules and PFIC considerations. The non-American partner’s investment choices become constrained by the American partner’s tax obligations.

The solution: invest separately. The American partner uses a US brokerage (Interactive Brokers, Charles Schwab, Fidelity) with US-domiciled funds. The non-American partner uses whatever brokerage and fund structure is optimal for their nationality and tax residency. For detailed PFIC guidance, see How to Invest as a US Expat.

FBAR and FATCA Reporting

The American partner must report foreign financial accounts (FBAR if aggregate value exceeds $10,000) and foreign financial assets (Form 8938 if thresholds are met). Joint accounts with the non-American partner count toward these thresholds. Even if the non-American partner contributed all the funds, the American partner must report the account.

This creates a reporting burden that some couples manage by minimizing the American partner’s foreign account exposure — keeping their money primarily in US-based accounts and using the non-American partner’s accounts for local spending.

For step-by-step FBAR filing instructions, see How to File FBAR as an Expat.

Property Ownership Across Borders

Owning property together as a mixed-nationality couple raises questions about title, tax, and inheritance.

How to Hold Title

Property ownership structures vary by country. Common options:

Tax Implications

Rental income from jointly owned property is typically split according to ownership shares and taxed in both partners’ jurisdictions. Capital gains on sale are similarly split. If the property is in a country where neither partner is tax resident, the property country may impose its own taxes, with relief available under tax treaties.

For US persons, the property’s value in USD must be tracked using the exchange rate at acquisition (for cost basis) and at sale (for proceeds). This can create a taxable gain from currency movement alone, even if the property’s local-currency value was flat.

For more on tracking cross-border property, see How to Track Real Estate Investments Across Countries.

Inheritance and Estate Planning

This is where mixed-nationality couples face the most complex legal terrain. Different countries have different rules about inheritance:

The EU Succession Regulation (Brussels IV) allows EU residents to choose whether the law of their nationality or the law of their habitual residence governs their succession. This is helpful for mixed-nationality couples in Europe but does not apply outside the EU.

Get a cross-border estate plan. This is one area where DIY is genuinely risky. A will that is valid in one country may not be recognized in another. You may need separate wills for assets in different jurisdictions, coordinated to avoid conflicts. Consult a lawyer who specializes in cross-border estate planning.

Managing Currency Risk as a Couple

With income, spending, and assets potentially spread across three or more currencies, mixed-nationality couples face amplified currency risk compared to individuals.

Align currency exposure with future plans. If you plan to retire in the United Kingdom, building GBP-denominated assets makes sense regardless of where you live now. If your future is uncertain, diversifying across currencies provides optionality.

Avoid unnecessary conversions. If one partner earns in EUR and the other in USD, and your spending is in EUR, the USD earner should convert to EUR for spending while the EUR earner avoids conversion entirely. See How Currency Exchange Rates Affect Your Investment Returns for more on managing FX impact.

Consider each partner’s pension and retirement entitlements. A British partner may have a UK state pension denominated in GBP. An Australian partner may have superannuation in AUD. These future income streams are effectively currency positions that should factor into your overall allocation.

Tracking Your Combined Finances

The operational challenge for mixed-nationality couples is seeing the full picture. You have individual accounts in different countries, shared spending accounts, investments in different currencies, property in yet another currency, and retirement accounts scattered across jurisdictions.

A spreadsheet can handle this for a while, but it breaks down as complexity grows. You need a tool that can hold all these accounts, convert everything to your chosen base currency, and show your combined net worth accurately.

FlashFi tracks investments, cash, savings, and debt across any currency, converting everything to your home currency automatically. Each partner can see how their individual accounts contribute to the combined financial picture.

Start tracking your finances together — one dashboard for two passports.

By David Brougham