French Tax Residence and Article 6(4) CGI: A Strategic Tool for Cross-Border Couples

I. Tax Residence Under French Domestic Law: A Flexible Concept

A. The Four Alternative Criteria of Article 4 B CGI

Article 4 B of the CGI defines tax domicile (domicile fiscal) in France through four alternative — not cumulative — criteria. Satisfying any single criterion is sufficient for the French tax authorities to treat the taxpayer as fiscally domiciled in France and, consequently, subject to taxation on their worldwide income under Article 4 A CGI.

Household or principal place of stay (foyer ou lieu de séjour principal). The household criterion refers to the place where the taxpayer or their family ordinarily lives, provided this residence has a permanent character. This is the criterion that creates the most difficulties for international couples: when one spouse expatriates while the other remains in France with children, the French tax authorities systematically consider the household to be located in France. The principal place of stay is a subsidiary criterion, applicable only to taxpayers who do not have an identifiable household; it targets individuals whose residence is split across several countries and who spend the majority of their time in France.

Principal professional activity (activité professionnelle à titre principal). A person who exercises a professional activity in France — whether salaried or self-employed — on a non-incidental basis is considered fiscally domiciled in France (CGI, art. 4 B, 1-b). The principal or incidental nature of the activity is assessed by comparison with activities exercised in other states, taking into account time spent and income generated. The 2020 Finance Act expanded this criterion to expressly cover directors of major French companies, who are presumed to exercise their principal activity in France as long as the company's registered office is located there.

Centre of economic interests (centre des intérêts économiques). This criterion corresponds to the place where the taxpayer has made their principal investments, where they hold the seat of their business, from where they administer their assets, or from where they derive the majority of their income. The Conseil d'État (France's supreme administrative court) brought a fundamental clarification: to establish that the centre of economic interests is in France, it is not sufficient to demonstrate the existence of significant French-situs assets; the authorities must verify that those assets actually produce income and compare that income to earnings from other countries (CE, 9th and 10th chambers, 7 October 2020, No. 426124). Real estate wealth held in France but generating little or no income does not, on its own, establish the centre of economic interests.

Government officials posted abroad (agents de l'État). Government officials exercising their functions abroad and not subject to personal income tax on their worldwide income in the host country are deemed fiscally domiciled in France (CGI, art. 4 B, 2). This criterion primarily concerns diplomats and seconded civil servants.

These four criteria cast a wide net. In practice, the French tax authorities have substantial powers of reclassification, and litigation most frequently revolves around the household and centre of economic interests criteria — both of which involve an irreducible element of subjective assessment.

B. The 2025 Reform: Statutory Enshrinement of Treaty Primacy

Article 83 of the 2025 Finance Act introduced a landmark amendment to Article 4 B CGI. Until then, the relationship between domestic tax domicile and treaty-determined tax residence had been the subject of growing jurisprudential uncertainty.

This uncertainty stemmed from a notable decision by the Conseil d'État dated 5 February 2024 (CE, 8th-3rd combined chambers, No. 469771). In that case, a corporate officer residing in Switzerland within the meaning of the Franco-Swiss tax treaty was nevertheless considered fiscally domiciled in France under Article 4 B CGI on the ground that he exercised a principal professional activity there. The Conseil d'État had accepted that a taxpayer could simultaneously be a non-resident under treaty law and domiciled in France under domestic law, with distinct tax consequences depending on the specific levies at issue — particularly the withholding tax on non-resident salaries.

The legislature put an end to this potentially destabilising duality. Since 1 January 2025, Article 4 B CGI expressly provides that a person who is not considered a French tax resident under an applicable international tax treaty cannot be regarded as fiscally domiciled in France, even if they satisfy one of the domestic law criteria. This reform enshrines the principle of treaty residence override and definitively closes the gap opened by the Conseil d'État's case law.

For cross-border couples, this reform has an immediate consequence: if one spouse is recognised as a resident of another state under a bilateral tax treaty, that spouse can no longer be considered fiscally domiciled in France. This clarification reinforces the importance of conducting a rigorous treaty analysis as the first step in any tax planning strategy.

II. The International Treaty Framework: Tie-Breaker Rules and Treaty Override

A. Article 4 of the OECD Model and the Hierarchy of Tie-Breaker Criteria

When a taxpayer qualifies as a resident of two states under their respective domestic legislation, bilateral tax treaties provide tie-breaker rules to determine a single state of residence. Article 4(2) of the OECD Model Tax Convention establishes a strict hierarchy of criteria that must be applied sequentially — the next criterion is only considered if the preceding one fails to resolve the conflict.

First criterion: permanent home. The taxpayer is deemed resident of the state where they have a permanent home available to them. If the taxpayer has a permanent home in both states, the analysis moves to the next criterion. The concept of permanent home is broader than mere domicile: it encompasses any dwelling that the taxpayer has arranged and maintains on a permanent basis for their use, whether as owner, tenant, or even gratuitous occupant.

Second criterion: centre of vital interests. If the taxpayer has a permanent home in both states (or in neither), they are deemed resident of the state with which their personal and economic relations are closest. This criterion integrates two dimensions: personal ties (family, social relations, cultural and political activities) and economic ties (location of assets, income sources, business activities). The OECD Commentary indicates that where a person maintains a home in one state where their family lives while working in another, the centre of vital interests will generally be considered to be in the first state. This presumption is rebuttable, however: the taxpayer can demonstrate that the preponderance of their vital interests lies in the host state.

Third criterion: habitual abode. If the centre of vital interests cannot be determined, or if the taxpayer has no permanent home in either state, the tie is broken in favour of the state in which the taxpayer has a habitual abode. This involves a quantitative comparison of days spent in each state. Contrary to a persistent misconception, there is no automatic 183-day threshold; the Conseil d'État has confirmed that the total duration of stays need not exceed 183 days to establish residence (CE, 16 July 2020, No. 436570).

Fourth criterion: nationality. If the habitual abode test does not resolve the dual residence, the taxpayer is deemed resident of the state of which they are a national. As a last resort, if none of these criteria produces a result, the competent authorities of the two states must settle the matter by mutual agreement procedure (MAP).

B. The Subsidiarity Principle and the Interaction Between Domestic and Treaty Law

The interaction between French domestic tax law and international treaties follows the subsidiarity principle, established by the landmark Conseil d'État decision in Schneider Electric (CE, full assembly, 28 June 2002, No. 232276). This principle requires a two-step analysis: first, the authorities must verify whether the taxpayer is liable to tax in France under domestic law; only then may they examine whether an international tax treaty bars that taxation.

In practice, the tax authorities must first establish that the taxpayer is fiscally domiciled in France under Article 4 B CGI. If so, they must then determine whether a bilateral treaty assigns residence to another state. Before the 2025 reform, this sequence could produce paradoxical outcomes: a taxpayer could be domiciled in France under domestic law while simultaneously being a treaty resident of another state, with different tax consequences depending on the levies involved. The 2025 amendment to Article 4 B resolved this duality by providing that treaty residence now overrides domestic tax domicile for all taxes.

For practitioners, this means a three-step analysis is essential: (1) verify whether the taxpayer meets any of the Article 4 B CGI criteria; (2) identify the applicable tax treaty and apply the tie-breaker rules; (3) since 2025, conclude that if the treaty assigns residence to the other state, the taxpayer is not fiscally domiciled in France, even under domestic law. This sequence is particularly decisive for cross-border couples, as it conditions the ability to invoke Article 6(4) CGI.

It is also important to note that certain bilateral treaties depart from the OECD Model on significant points. The Franco-UAE treaty of 19 July 1989, for example, does not contain a symmetrical tie-breaker clause: dual residence must be resolved through mutual agreement between the competent authorities. Similarly, the Franco-American treaty applies specific tie-breaker criteria that do not precisely follow the OECD Model hierarchy. These particularities require a treaty-by-treaty analysis, with no automatic transposition of general principles.

III. Article 6(4) CGI: A Strategic Lever for Cross-Border Couples

A. Conditions and Scope of the Mechanism

Article 6 CGI establishes the principle of joint household taxation (imposition commune) for married couples and civil partners (PACS). This principle is subject to three mandatory exceptions under paragraph 4. Spouses are taxed separately when: (a) they are married under a separate property regime and do not live under the same roof; (b) they are involved in judicial separation or divorce proceedings and have been authorised to maintain separate residences; or (c) where one spouse has abandoned the marital home and each has separate income.

The most relevant scenario for cross-border couples is the first: the combination of a separate property regime and genuinely distinct residences. Two cumulative conditions must be satisfied.

First condition: separate property matrimonial regime. The spouses must be married under a separate property regime (régime de séparation de biens), whether this results from an initial marriage contract or a subsequent change of regime. The participation in acquisitions regime (Zugewinngemeinschaft), which operates as the default regime in certain foreign jurisdictions (Germany, Switzerland), may raise classification difficulties: it is necessary to verify whether French private international law treats it as a separatist regime for the purposes of Article 6(4). Case law adopts a functional approach: the decisive factor is the absence of communal property during the marriage.

Second condition: genuinely separate and non-temporary residences. The spouses must reside under different roofs, and this separation must not be temporary or accidental. The French tax administration's official commentary (BOFiP) specifies that the separation must result from an effective breakdown of the common household, not from a mere temporary professional absence. In other words, an executive who spends weekdays in London for work and returns to their spouse in Paris at weekends does not satisfy this condition. However, a couple where one spouse is permanently established in Dubai with their own accommodation while the other resides full-time in Paris does meet the requirement.

Evidence of separate residence may be provided by any means: separate lease agreements, utility bills, residence certificates issued by foreign authorities, consular registration, or even witness statements. The Conseil d'État has held that the burden of proof lies with the taxpayers claiming separate taxation (CE, 12 March 2010, No. 311121), but the administration cannot reject the claim solely because the spouses maintain affective ties or cooperate in managing common financial interests. The case law is consistent on this point: spouses married under a separate property regime who reside under different roofs must be taxed separately, even if they act jointly in managing common material interests and visit each other on the occasion of professional trips.

B. Anonymised Case Studies: How Article 6(4) CGI Changes the Outcome

Case 1 — The executive relocated to a Gulf jurisdiction. A taxpayer, a consulting firm director, relocates with his wife to a Gulf state. After several years, the wife decides to return to France with their children for family reasons. The couple, married under a community property regime (communauté légale), is then jointly assessed to tax in France — the administration considers the household to be in France given the wife and children's presence there. The taxpayer contests this, invoking the bilateral treaty. But as long as the couple falls under the community property regime, joint taxation applies: the resident spouse in France triggers taxation of the entire household. The taxpayer eventually prevails on treaty grounds — the convention assigns residence to the Gulf state — but the dispute spans several years and requires considerable resources. Had the couple adopted a separate property regime before the wife's return to France, Article 6(4) CGI would have enabled separate taxation from the outset, avoiding the litigation entirely.

Case 2 — The senior executive between France and Switzerland. A senior executive works in Switzerland, where he resides for most of the year in a rented apartment. His wife, married under a separate property regime, lives in Paris with their children. The French tax authorities issue a joint assessment on worldwide income, considering the household to be in France under Article 4 B CGI. The taxpayer first invokes the Franco-Swiss treaty to establish his residence in Switzerland, then relies on Article 6(4) CGI to obtain separate taxation from his wife. The Administrative Court of Appeal rules in his favour on both points: the treaty assigns residence to Switzerland (permanent home in both states, but centre of vital interests in Switzerland given his principal professional activity and income), and Article 6(4) applies since both conditions — separate property regime and separate residences — are met. The wife is taxed in France solely on her own income, retaining the family quotient benefit for dependent children.

Case 3 — Reclassification of the centre of economic interests. A couple in which one spouse conducts a consulting business from an Asian jurisdiction while the other resides in France holds substantial real estate in France. The tax authorities attempt to establish the expatriate spouse's fiscal domicile in France on the basis of the centre of economic interests, relying on the value of the French real estate portfolio. In line with the Conseil d'État's ruling (CE, 7 October 2020, No. 426124), the administrative tribunal requires the authorities to demonstrate that this portfolio actually produces income exceeding earnings from abroad. In the case at hand, the French real estate constitutes the wife's principal residence and generates no rental income, while the household's primary income derives from the professional activity conducted in Asia. The taxpayer prevails: the centre of economic interests is not in France. Combined with Article 6(4) CGI — the couple being married under a separate property regime — separate taxation is secured, and only the wife's French-source income is taxed in France.

C. Practical Recommendations: Planning Ahead Rather Than Reacting

Litigation experience highlights several lessons that every cross-border taxpayer should incorporate into their fiscal planning.

Adopt or adjust the matrimonial regime before expatriation. Article 6(4) CGI can only be invoked if the spouses are married under a separate property regime. Changing the matrimonial regime during marriage requires a notarial deed and, in some cases, judicial approval. This process takes several months. It is therefore essential to plan ahead — before departure or, at the very least, before any event likely to trigger a tax audit (a spouse's return to France, an asset disposal, etc.).

Build a robust evidence file from day one. Case law requires the separation of residence to be effective, lasting, and non-temporary. In practice, this means assembling and preserving a comprehensive body of corroborating evidence: lease agreements or title deeds in each state, bank statements showing current expenditure in each location, residence certificates from local authorities, consular registration, children's school enrolment, health insurance contracts, and local phone subscriptions. The more complete the file, the harder it will be for the administration to challenge the reality of the separation.

Analyse the applicable bilateral treaty before any structuring. Each tax treaty has its own specificities. Tie-breaker rules are not uniform: some treaties faithfully follow the OECD Model, while others depart from it significantly. The analysis must cover the treaty text itself, any additional protocols, interpretive exchanges of letters, and case law from both contracting states. Since 2025, the treaty's role is further strengthened as treaty residence now overrides domestic tax domicile.

Do not overlook filing obligations. Separate taxation under Article 6(4) CGI requires the filing of two separate income tax returns. The resident spouse declares their personal income and the income of dependent children. The non-resident spouse, if they receive French-source income, must file a specific return with the non-resident tax office (Service des Impôts des Non-Résidents, SIPNR, in Noisy-le-Grand). Any omission or inconsistency in filings can attract the administration's attention and weaken the taxpayer's position in the event of an audit.

Consider the implications for wealth tax and gift/inheritance tax. Separate taxation for income tax purposes does not predetermine the treatment for French real estate wealth tax (IFI) or gift and inheritance tax (droits de mutation à titre gratuit). Article 964 CGI provides that married couples are jointly assessed to IFI unless they are married under a separate property regime and do not live under the same roof — a condition identical to that of Article 6(4). Consistency across the various taxes argues for a holistic approach to the couple's asset structuring.