You moved to France years ago, built a life in Lyon, Toulouse or the Dordogne, and kept the house you used to live in back in Britain. Now a buyer has made an offer on that Manchester terrace, that Bristol flat or that cottage in Kent, and a hard question lands on your desk: two countries want a share of the gain, and each has its own return, its own deadline and its own calculation. France taxes its residents on their worldwide income, so the sale of a foreign property is declared in France. The United Kingdom taxes non-residents on British land, with a strict online return due within weeks of completion. Since Brexit nothing in this architecture has softened: you file in both countries, and a bilateral treaty decides who taxes what and how the second bill is reduced by the first. Get the order wrong and you pay twice, or you pay late with interest and penalties on one side of the Channel. This guide explains the full path in plain English, with the exact legal texts behind every step. Part I covers the French side: how residence is decided and how Paris computes the gain. Part II covers the British side and the treaty: the 60-day return, the reliefs, the credit that prevents double taxation, and what to do when an assessment looks wrong.

I. How France taxes the sale of your British property while you live in France

A. Are you a French tax resident on the day of the sale, and why keeping a house in Britain changes nothing

Everything starts with one question: where is your domicile fiscal, your tax residence, on the day the sale completes. French law answers it without any regard for your passport. Article 4 A of the Code général des impôts, the French tax code, states the worldwide principle in one sentence: “Les personnes qui ont en France leur domicile fiscal sont passibles de l’impôt sur le revenu en raison de l’ensemble de leurs revenus.” If France is your tax home, you owe French income tax on all of your income, including the gain on a house in Leeds. People whose tax home sits outside France, by contrast, owe French tax only on French-source income. So the whole edifice turns on residence, and residence is decided by three tests set out in article 4 B of the same code: “1. Sont considérées comme ayant leur domicile fiscal en France au sens de l’article 4 A : a. Les personnes qui ont en France leur foyer ou le lieu de leur séjour principal ; b. Celles qui exercent en France une activité professionnelle, salariée ou non, à moins qu’elles ne justifient que cette activité y est exercée à titre accessoire ;” […] “c. Celles qui ont en France le centre de leurs intérêts économiques.” In plain terms: your foyer, the home where your family life is centred, or the place where you spend most of the year; your main professional activity; or the centre of your economic interests. Meet any one of the three and France treats you as resident.

Two features of that rule matter enormously for British sellers. First, the three tests are alternatives, not a cumulative checklist. The administrative court of appeal of Versailles said so word for word in a residence dispute between the tax authority and a couple who had moved abroad: “Ces critères sont alternatifs et non cumulatifs.” The judgment (Versailles, 21 March 2023, RG 20/00185) deserves attention for a second sentence that answers the objection every British owner raises: surely keeping my UK house keeps me British for tax purposes. The court replied that “aucun de ces critères ne porte sur la qualité de propriétaire immobilier”, none of the tests turns on whether you own bricks and mortar somewhere. Owning the house you are about to sell does not make you a British resident, and selling it does not by itself make you French. What counts is where you actually live, work and centre your interests: the family home in France, the children in a French school, the French employment contract or business, the registration with the French health system, the bills and bank life that show day-to-day presence. The court added that habitual residence “s’apprécie au regard des éléments probants que produit le contribuable”, it is assessed on the evidence the taxpayer produces. Keep that sentence in mind, because in a dispute the burden of proof is practical: electricity and water bills, school certificates, travel records, health cover documents and employer attestations decide the case long before legal theory does.

Do not confuse this tax residence with your civil domicile, the notion found in article 102 of the Code civil, which provides that “Le domicile de tout Français, quant à l’exercice de ses droits civils, est au lieu où il a son principal établissement.” That rule governs civil matters such as where you can be served with court papers. Tax residence follows its own tests in article 4 B, and the two can point in different directions. A British national can easily be domiciled in France for civil purposes and resident in France for tax purposes at the same time, while remaining a British citizen throughout. Citizenship plays no role in the analysis.

Where both countries claim you, the treaty signed in London on 19 June 2008 between France and the United Kingdom, published in France by decree and available in full on the official legal database, contains tie-breaker rules that allocate residence to one side only. Article 4 B itself warns that persons who meet a French test “ne peuvent toutefois pas être considérées comme ayant leur domicile fiscal en France lorsque, par application des conventions internationales relatives aux doubles impositions, elles ne sont pas regardées comme résidentes de France”, cannot be treated as French-resident where an applicable double-tax treaty deems them resident elsewhere. In practice the tie-breaker looks first for a permanent home in one country, then for the centre of vital interests, then for habitual presence. Most Britons settled in France with their family pass these tests on the French side without difficulty, which means the sale of the UK property falls squarely into worldwide French taxation. The same residence logic already decided the tax treatment of British rental income from a UK letting, as explained in our companion guide on declaring UK rental income as a French resident and claiming the treaty credit, and the reasoning carries over in full to a sale.

B. How Paris computes the gain on a foreign sale: price, costs, allowances, rates and the notary’s form

Once residence points to France, the sale is taxed under the ordinary French regime for property gains, even though the bricks stand in Britain. Article 150 U of the tax code casts the net deliberately wide: “les plus-values réalisées par les personnes physiques […] lors de la cession à titre onéreux de biens immobiliers bâtis ou non bâtis ou de droits relatifs à ces biens, sont passibles de l’impôt sur le revenu dans les conditions prévues aux articles 150 V à 150 VH”. Gains made by individuals on the sale for consideration of built or unbuilt property are liable to income tax. Nothing in that charge is limited to French soil, and that is exactly why a French resident selling a house in Sheffield owes French tax on the profit. The same article lists the exemptions, and the first one is the trap for the unwary: “1° Qui constituent la résidence principale du cédant au jour de la cession”, property that is the seller’s main home on the day of sale. Your main home is the dwelling you actually occupy for most of the year, and the official English-language guidance on service-public.fr confirms you are fully exempt on the sale of your primary residence and its outbuildings. A house in Britain where you no longer live, while your family home is in France, cannot qualify. Some sellers hope to use the first-sale reinvestment relief, which exempts the gain where you plough the price back into a main home within two years and have not owned that main home during the previous four years. The relief exists, but it is granted once only, on request through a statement in the sale deed, and it assumes a fact pattern, a renter buying a first main home, that rarely matches a British owner who already owns in France. Check the two conditions against your own history before relying on it, because an unjustified claim is reassessed with interest.

The computation itself follows a simple skeleton with generous, proof-driven flesh. You start from the sale price stated in the deed, then subtract the acquisition price, meaning what you actually paid as shown in your purchase deed, plus the costs the rules allow you to add. The official guidance explains that the purchase price can be increased, on proof or at a flat rate, by acquisition fees for their actual justified amount or for a lump sum of 7.5% of the purchase price, which covers stamp duty land tax, solicitor and agency fees on the way in. Works expenditure, building, reconstruction, extension or upgrading, counts too, either at its real justified amount or at a flat 15% of the purchase price where the property has been held for more than five years. For a British sale this is where files are won or lost from Paris: keep the completion statement from your solicitor, the invoices for the extension or the new roof with proof of payment, and the surveyor reports, because the French inspector cannot visit the property and will judge the file on paper. Convert every sterling figure with a consistent, documented exchange rate and keep the rate source with the return. After costs comes the holding-period allowance, the abattement pour durée de détention, which reduces the taxable base the longer you have owned the property. The official position is straightforward: you are exempt from tax on real estate capital gains for any property held for more than 22 years, and capital gains on property held for more than 30 years are also exempt from social security contributions. Between purchase and those horizons, each additional year of ownership shaves the bill, which is why the exact acquisition date on your old deeds matters as much as the sale price.

On the resulting net gain, two layers of tax apply. First, income tax at a flat rate: the capital gain on real estate, after deduction of the allowance, is taxed at the rate of 19%, so for a taxable gain of 20,000 euros the income tax is 3,800 euros. Second, the social levies, the prélèvements sociaux, which fund French social protection: you must pay social security contributions at the rate of 17.2%, so for a taxable gain of 20,000 euros the levies are 3,440 euros, a combined 7,240 euros. The legal base for that second layer sits in article L. 136-6 of the Code de la sécurité sociale, which provides that “Les personnes physiques fiscalement domiciliées en France au sens de l’article 4 B du code général des impôts sont assujetties à une contribution sur les revenus du patrimoine assise sur le montant net retenu pour l’établissement de l’impôt sur le revenu” […] “e) Des plus-values, gains en capital et profits soumis à l’impôt sur le revenu”. Because you are a French tax resident within article 4 B, the British gain sits in that base. On top of both layers, very large gains attract an additional surtax: an additional tax applies where the taxable gain exceeds 50,000 euros, at rates from 2% to 6% according to the amount. The calculation table appears on form 2048-IMM-SD, and the official guidance notes that in practice it is calculated by the notary. That sentence describes a French sale handled by a French notaire, the public officer who collects the tax at the signing table. In a British sale there is no French notary at completion, so nobody withholds the French tax for you. You compute, you declare and you pay through your French income tax return, in the section for foreign-source income, keeping the British completion accounts as your proof. Interest for late payment runs from the legal due date whether or not anyone reminded you, so diary the French filing deadline as carefully as the British one.

For contrast, two neighbouring provisions show how deliberately the code separates your situation from that of a non-resident. Article 164 B lists the income treated as French-source for people who live abroad, and article 244 bis A opens with “Sous réserve des conventions internationales”, subject to the treaties, and provides that the gains it covers “sont soumises à un prélèvement selon les taux fixés au III bis”, are subject to a levy at the rates it sets. That withholding-style levy, applied “sous réserve des conventions internationales”, subject to the treaties, is the regime of the seller who has left France. It is not yours. As a French resident you are taxed on the worldwide gain with a credit for the British tax, which is the subject of Part II. But the comparison carries a warning for mobile families: if you sell the year you move countries, each side may claim a different status for the same sale, and only the treaty tie-breaker plus careful dating of departure and arrival settles the conflict. The mirror case, leaving France for Britain and selling the old French home from abroad, follows different exemption windows and a capped relief of its own, and is examined in our guide on selling a former French home after returning to Britain.

II. How the United Kingdom taxes the same sale and how the treaty prevents paying twice

A. The 60-day British return, the reliefs that shrink it, and the six-year tail that follows leavers

Britain taxes the land, not the person. Since April 2015 for residential property, a seller who is not resident in the United Kingdom for tax purposes still owes capital gains tax on a British home, and since April 2020 the machinery has been unforgiving: HM Revenue and Customs, the British tax authority, requires a standalone online return within weeks of the sale, separate from any self-assessment cycle. The official instruction leaves no room for doubt: any capital gains tax due on British residential property must be reported and paid through the dedicated online account within 60 days of completion, as explained on the GOV.UK page for sellers of UK property, which also warns of interest and penalties for late filing and late payment. Completion means the day the sale legally completes, not the day you accept the offer and not the day the money reaches your account. Open the capital gains account on GOV.UK before exchange if you can, because identity checks and access codes take time, and the 60 days run through holidays. Where the property was jointly owned, each owner reports only their own share of the gain. Where you give the property to a spouse, a civil partner or a charity rather than selling it, different rules apply, so confirm the character of the transfer before choosing the form. If you already file British self-assessment returns, for example for rent received before the sale, you must still file the 60-day property return first and then repeat the figures in the annual return.

The British gain is not always the same number as the French gain, and the gap surprises many sellers. Britain starts from sale proceeds minus acquisition cost and allowable costs, then applies its own reliefs, of which the most valuable is private residence relief for the years the property was your only or main home, plus a short final period fixed by HMRC rules. Check the current length of that final period on GOV.UK before filing, because it has changed in the past and applying an outdated figure is a classic source of penalties. Letting relief may also apply in narrow cases where you once shared occupation with a tenant. The annual exempt amount, the British tax-free slice of gains, can absorb small profits, and its level changes between tax years, so verify the figure for the year of completion rather than the year you bought. None of these reliefs exists in French law in the same form, and none of the French allowances exists in British law, which is why the taxable base differs on each side and why the treaty credit described below is capped rather than automatic. Keep one consistent set of underlying documents, purchase deed, sale contract, improvement invoices, dates of occupation, and then run the two computations separately.

The treaty itself confirms that Britain is entitled to tax the sale. The convention signed on 19 June 2008, published in the Journal officiel and freely available on the official legal database at Décret n° 2010-20 du 7 janvier 2010 portant publication de la convention franco-britannique, provides in its article 14, headed capital gains, that gains from selling land situated in one of the two countries may be taxed there, while gains on other kinds of property stay taxable only in the seller’s country of residence, as summarised in the official doctrine presentation of the France-United Kingdom income tax convention of 19 June 2008. Shares in a property-rich company and interests in partnerships or trusts holding British land are swept into source taxation by paragraph 2 of the same article, so holding the house through a vehicle rarely escapes the British charge. Then comes a sting in paragraph 6 that every recently departed seller must read twice: each country keeps, for six tax years, a residual right to tax gains realised by someone who is or was its resident at any point during those six years. A country keeps for six tax years a residual right to tax gains of someone who was its resident. In practice this six-year tail matters most in the mirror situation, a former French resident now back in Britain selling what is left behind, and it is examined in detail in our guide on the six-year treaty tail for leavers selling a former French home. For your sale as a French resident, the tail confirms the symmetry of the system: each country guards its former residents for a while, and the credit mechanism below is what keeps the total burden fair.

One boundary deserves a clear sentence because it generates expensive confusion. French social levies on the gain depend on your affiliation to a social security system, and disputes about which system covers you are decided by the French courts under European coordination rules. The second civil chamber of the Cour de cassation, the supreme court for civil and social matters, ruled twice on 25 September 2025, pourvois 22-24.634 and 22-20.036, on claims for reimbursement of French health contributions by people affiliated abroad, and in the first case it “DIT n’y avoir lieu à renvoi préjudiciel à la Cour de justice de l’Union européenne ; REJETTE le pourvoi”, refused to refer the European question and dismissed the appeal. Since Brexit, British cover through the NHS no longer counts as affiliation within the European coordination system, so a French resident cannot escape the 17.2% on the strength of being treated in Britain. If your file raises an affiliation argument, for example a posted worker holding an A1 certificate or a pensioner carrying an S1 healthcare form, document it separately from the capital gains computation, because it follows its own procedural track before the social courts.

B. The French credit for the British tax paid, its cap, and how to challenge a refusal or a double bill

Because both countries may tax the same gain, article 24 of the convention, headed elimination of double taxation, gives France a precise instruction. For income of the kind at stake here, the resident of France is entitled to a credit against French tax equal to the tax paid in Britain in accordance with the treaty, capped at the amount of the French tax on the same gain, as set out in the official presentation of the France-United Kingdom convention. Three consequences follow. First, the credit covers only tax paid in Britain in accordance with the treaty, so the 60-day return must be correct in its own right before it can shelter anything in France. Second, the credit cannot exceed the French tax on the same gain, which means any excess British tax is a dead cost, not a refund, and the two computations should be modelled together before completion so that no restructuring surprise appears afterwards. Third, the treaty states elsewhere in the same article that the British tax is not deductible from the income itself, only creditable against the French tax, so do not subtract the HMRC payment from the gain and then claim the credit on top. The practical order is therefore fixed: complete the sale, file and pay the British return within 60 days, then declare the worldwide gain in France with the British assessment attached and the credit claimed. Keep the HMRC payment receipt, the sterling-to-euro conversion evidence and the completion statement together, because the French inspector will ask for all three, and a credit claimed without proof is routinely refused.

French courts read tax treaties the way they read statutes: literally, and by reference to French domestic law for any term the treaty does not define. The commercial chamber of the Cour de cassation recalled the method on 6 May 2026, pourvoi 24-22.185, in a dispute about treaty interpretation, quoting the standard renvoi clause found in French conventions: “pour l’application de celle-ci à un moment donné par un Etat contractant, tout terme ou expression qui n’y est pas défini a le sens que lui attribue le droit de cet Etat, à moins que le contexte n’exige une interprétation différente”. For your file the lesson is concrete: cite the treaty article numbers in your correspondence, attach the British assessments that prove the tax was paid in accordance with those articles, and define every disputed term by the French code provision that supplies its meaning. A claim that merely says double taxation is unfair, without pointing to article 14 for the charge and article 24 for the credit, carries little weight with either administration.

When an assessment looks wrong, each country offers its own remedy and the two should be run in parallel. On the French side, the réclamation contentieuse, the formal claim to the tax authority, is the mandatory first step before any court action. File it in writing, identify the tax notice, the year and the amount disputed, set out the treaty articles and attach the British return, the payment receipt and the computation. Respect the deadline printed on your avis d’imposition, the tax notice, because it is peremptory: a late claim fails whatever its merits. If the claim is rejected expressly or by silence, the dispute moves to the administrative court, where the same file, residence evidence plus treaty analysis, is pleaded again. On the British side, an error in the 60-day return can be corrected through the correction facility in your HMRC property account within the window shown there, and a formal assessment can be appealed to the tax tribunal within the deadline stated on the decision letter. Where the two administrations disagree about the treaty itself, for instance about which country was entitled to tax or about the size of the credit, article 26 of the convention, headed mutual agreement procedure, allows the two competent authorities to settle the case together while domestic remedies continue. Ask your adviser to mention it explicitly in both files so that neither side treats the parallel procedure as an admission.

Four recurring mistakes account for most of the reassessments seen in these files. The first is forgetting the French declaration altogether on the theory that tax paid in Britain ends the matter. It does not: France taxes the worldwide gain and grants the credit only if claimed. The second is claiming the main-home exemption for the British house while the family lives in France. The exemption requires the property to be your main home on the day of sale, and a selective reading of article 150 U will not survive the inspector’s questions about schools, bills and health cover. The third is missing the 60-day British deadline while waiting for French paperwork. The British clock starts at completion and ignores the French timetable entirely, so interest and penalties accrue while you gather translations. The fourth is currency chaos: converting the purchase price at one rate, the sale price at another and the British tax at a third, without keeping any source. Pick the rates published by a single authoritative source for each relevant date, keep screenshots or printouts, and apply them consistently across both returns. A file with clean conversions and complete British receipts is the file that gets its credit without a fight.

Conclusion

Selling a British property from a French home means satisfying two sovereigns in a fixed order: Britain first within 60 days of completion, France second through the worldwide return with the treaty credit claimed and proved. Residence is decided by the three alternative tests of article 4 B, ownership of the British house changes nothing, the French gain follows article 150 U with its allowances, its 19% rate, its 17.2% levies and its surtax on large profits, and the convention allocates the taxing right to Britain under article 14 while obliging France to credit the British tax under article 24 up to the French amount. Build the file as if both inspectors will read it, because both will: dated residence evidence, complete British completion accounts, consistent currency conversions, the HMRC return and receipt, and treaty articles cited by number in every letter. Done this way, the sale closes a chapter cleanly instead of opening two disputes, and the gain is taxed once in substance, shared between the two treasuries exactly as the treaty intends.