You arrived from the United Kingdom in March, signed a French tenancy, registered with the local mairie (town hall), and opened a French current account for the rent and the bills. Your UK current account stayed open for the direct debits, your savings sat in a Cash ISA, and a small Stocks and Shares ISA held a handful of British shares. Then May came, and with it your first French income tax return. Nobody at the bank warned you. Nobody at the removal firm mentioned it. And somewhere between the form 2042, the form 2047 for foreign income and an annex numbered 3916, a quiet obligation was waiting that carries a 1,500-euro fine per account, an 80 per cent surcharge on the tax, and, in the worst cases, a legal presumption that the money in your undeclared account was a gift taxed at the highest rate. This guide explains, in plain English and with the exact French texts, who must declare, what France taxes inside your ISA, and how to regularise a late declaration or challenge the bill step by step.

I. I Forgot to Declare My UK Bank Account in France: Who Must File Form 3916 and Which Income Goes Where

A. Are You a French Tax Resident in Your Arrival Year: Home, Stay and Centre of Interests

Everything starts with one question, because the declaration duty only binds people who are domiciled or established in France for tax purposes. Article 4 B of the French Tax Code (Code général des impôts, the CGI) sets three alternative tests, and meeting any single one is enough: «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», and the same paragraph adds a third test, «Celles qui ont en France le centre de leurs intérêts économiques.» In ordinary language: foyer means the home where your family life is centred, séjour principal means the place where you spend most of the year, and the centre of economic interests points to where your main investments and business ties sit.

For a British newcomer, the practical effect is blunt. If your spouse and children live with you in Lyon, Bordeaux or Paris while you keep a flat in London, your foyer is in France from the day they moved. If you live alone and spent more than half the year in France, your principal stay is in France. If you work for a French employer or run your activity from a French desk, the professional test bites too. Any one of the three makes you a French tax resident, and from that moment your worldwide income falls inside the French return. Article 158 of the CGI states the worldwide principle without ambiguity: «sans qu’il y ait lieu de distinguer suivant que ces revenus ont leur source en France ou hors de France.» There is no first-year grace period and no minimum threshold below which the declaration duty disappears.

Once residence is settled, the account duty follows automatically. Article 1649 A, second paragraph, of the CGI provides: «Les personnes physiques, les associations, les sociétés n’ayant pas la forme commerciale, domiciliées ou établies en France, sont tenues de déclarer, en même temps que leur déclaration de revenus ou de résultats, les références des comptes ouverts, détenus, utilisés ou clos à l’étranger.» Read that sentence twice, because British readers consistently misread it in three ways. First, «held, used or closed» means a closed account counts: shutting your UK account in February does not erase the duty for the year it was open. Second, duty is simultaneous: form 3916 (and its sibling 3916-bis for certain placements) travels with the annual return, normally filed online in May or June, through your personal space on the tax portal. Third, the duty covers every account «of any kind»: current accounts, savings accounts, share dealing accounts, and the cash hub that sits inside a Stocks and Shares ISA. The official page for form 3916 on impots.gouv.fr confirms the form and its scope, and the English-language service-public.fr guide on declaring accounts held abroad walks through who must file and how.

In practice, your first French return therefore has three layers. The form 2042 carries your total taxable income. The form 2047 (foreign income schedule) carries the detail of each category of UK-source income: interest, dividends, gains. And one form 3916 per UK account carries the administrative references: bank name, address, account number, opening date, and, where relevant, closing date. British clients often ask whether a dormant account with a few pounds still counts. The statute draws no de minimis line for the declaration itself: the references must be declared even if the account earned nothing. The amounts only matter for the tax computation and for the penalty, which is calculated per account, not per euro hidden.

B. Your ISA, Your Interest and Your Dividends: What France Taxes and What the Treaty Shields

The single most expensive misunderstanding in this whole area is the ISA. On the British side the position is genuinely generous. The official gov.uk guidance says you can «save tax-free» with an Individual Savings Account (ISA) Interest on a Cash ISA and gains inside a Stocks and Shares ISA escape UK income tax and capital gains tax, within the annual subscription limits. Many British savers reasonably assume the wrapper travels with them. It does not. French tax law does not recognise the ISA as a tax-exempt envelope. It looks straight through the wrapper and taxes each stream of income under its own heading, exactly as if the ISA did not exist.

Interest credited inside your Cash ISA is the simplest case. Article 120 of the CGI treats foreign-source investment income as taxable revenue, listing «Les dividendes, intérêts, arrérages et tous autres produits des actions de toute nature et des parts de fondateur des sociétés, compagnies ou entreprises financières, industrielles, commerciales, civiles et généralement quelconques dont le siège social est situé à l’étranger quelle que soit l’époque de leur création» Your ISA interest therefore joins your taxable income in France even though London charges nothing on it. The mechanism matters here. Article 125 A of the CGI imposes a levy collected at source only where the payer is established in France: «sont assujetties à un prélèvement lorsque la personne qui assure le paiement de ces revenus est établie en France» Your UK bank is not established in France, so no French withholding is taken during the year, and the full amount must be picked up on your return. Forget it, and the omission sits in the file until the administration finds it through the automatic exchange of bank information between the United Kingdom and France.

Dividends inside a Stocks and Shares ISA follow the same French logic with one treaty refinement. They are taxable in France, but the France–United Kingdom double tax treaty of 19 June 2008, published by decree in France, divides the taxing rights. Article 11 on dividends makes a British dividend paid to a French resident taxable in France, while letting the United Kingdom keep a capped withholding tax of up to 15 per cent of the gross dividend where the recipient is its beneficial owner, as set out in the France–United Kingdom tax treaty of 19 June 2008 In practice, a British company dividend paid to you as a French resident can suffer up to 15 per cent UK withholding, and France then taxes the gross dividend while granting relief for the British tax under the treaty’s elimination article. Two traps deserve attention. First, the old British dividend tax credit no longer helps: France’s own treaty commentary (BOI-INT-CVB-GBR) records that residents of France have not benefited from the British tax credit on dividends distributed since 18 December 2009, so there is nothing to add to the dividend and no matching credit to claim. Second, where UK withholding has genuinely been levied, keep the voucher: without proof of the foreign tax, the French inspector will refuse the credit and the same dividend is taxed twice in cash-flow terms until you produce it.

Interest is cleaner. Under Article 12 of the same treaty, interest arising in one contracting state whose beneficial owner lives in the other state is taxable only in that other state, which for a French resident means France alone UK-source interest belonging to a French resident is therefore taxable only in France. If your UK bank nevertheless deducted British withholding, that deduction is an error to reclaim on the British side through HMRC, not a credit to set against French tax. Do not mix the two treatments: dividends can carry a foreign tax credit, interest cannot, because only France is entitled to tax it.

Gains realised inside the Stocks and Shares ISA complete the picture. French law taxes «les gains nets retirés des cessions à titre onéreux, effectuées directement, par personne interposée ou par l’intermédiaire d’une fiducie, de valeurs mobilières, de droits sociaux» under article 150-0 A of the CGI, and selling shares inside the ISA is a disposal for valuable consideration even though no UK tax arises. The default French treatment of this investment income is the flat-rate levy, the prélèvement forfaitaire unique (PFU): article 200 A of the CGI provides that the income tax on the listed investment income and gains «est établi par application du taux forfaitaire prévu au B du présent 1», and paragraph B fixes that «taux forfaitaire» at «12,8 %.» Social charges (the prélèvements sociaux) apply on top, and you may instead elect for the progressive income-tax scale, the option globale for the scale mentioned in article 200 A, where your marginal rate and allowances make that cheaper. Readers who also draw UK rental income while living in France face a different schedule for that rent, explained in our companion guide on British landlords living in France and their UK rental income; keep the two computations separate, because the treaty assigns each category of income to its own article and its own relief method.

II. Challenging the Bill: Regularising a Late Declaration and Fighting the Fine Before the Judge

A. The Fine, the 80 per Cent Surcharge and the Donation Presumption: What Silence Really Costs

Clients usually discover the problem in one of two ways: a letter from the tax office asking about an account the exchange of information has already revealed, or a notice applying a fine they never saw coming. The scale starts with a fixed amount per account. Article 1736, IV, 2 of the CGI provides that «Les infractions aux dispositions du deuxième alinéa de l’article 1649 A et de l’article 1649 A bis sont passibles d’une amende de 1 500 € par compte ou avance non déclaré.» The same paragraph raises the stakes for opaque jurisdictions: «Toutefois, pour l’infraction aux dispositions du deuxième alinéa de l’article 1649 A, ce montant est porté à 10 000 € par compte non déclaré lorsque l’obligation déclarative concerne un Etat ou un territoire qui n’a pas conclu avec la France une convention d’assistance administrative en vue de lutter contre la fraude et l’évasion fiscales permettant l’accès aux renseignements bancaires.» The United Kingdom has concluded such an assistance convention with France, so the ordinary exposure for a British reader is 1,500 euros per undeclared account per year concerned, not 10,000. Count the accounts, not the balance: three forgotten accounts over two years can mean six fines. The administration’s English-language guide confirms the tariff in plain terms, with a «fine of €1,500 by undeclared account» rising to €10,000 per account only where the account sits in a state that has no tax-information assistance convention with France

The fixed fine is only the first layer. The same guide warns of an 80 per cent increase of the duties due on the sums held in the undeclared account or accounts, an increase that then replaces the flat fine of €1,500 or €10,000 Where the undeclared account held income that should have been taxed, the 80 per cent increase applies to the duties on those sums instead of the flat fine, which can dwarf 1,500 euros on a well-funded ISA or share account. Interest for late payment runs in addition. And behind both sits a heavier weapon that many advisers underrate: the presumption of a gift. Article 755 of the CGI provides that «Les avoirs figurant sur un compte détenu à l’étranger, au sens du deuxième alinéa de l’article 1649 A, […] dont l’origine et les modalités d’acquisition n’ont pas été justifiées dans le cadre de la procédure prévue à l’article L. 23 C du livre des procédures fiscales sont réputés constituer, jusqu’à preuve contraire, un patrimoine acquis à titre gratuit assujetti, à la date d’expiration des délais prévus au même article L. 23 C, aux droits de mutation à titre gratuit au taux le plus élevé mentionné au tableau III de l’article 777» In other words, unexplained money on a foreign account is deemed to be an inheritance or gift taxed at the top rate until you prove otherwise.

The procedure that leads there is tightly timetabled, and the timetable is your friend if you use it. Article L. 23 C of the Tax Procedures Book (Livre des procédures fiscales, the LPF) allows the administration, where the declaration duty has been missed at least once in the previous ten years, to demand explanations «indépendamment d’une procédure d’examen de situation fiscale personnelle», and to require the taxpayer «de fournir dans un délai de soixante jours toutes informations ou justifications sur l’origine et les modalités d’acquisition des avoirs figurant sur le compte» An incomplete answer brings a formal demand to complete it within thirty days, and article L. 71 draws the consequence: «En l’absence de réponse ou à défaut de réponse suffisante aux demandes d’informations ou de justifications prévues à l’article L. 23 C dans les délais prévus au même article, la personne est taxée d’office dans les conditions prévues à l’article 755 du code général des impôts.» Taxée d’office means assessed without your participation, on the administration’s figures, with your appeal rights narrowed to proving the assessment wrong.

Two recent rulings frame the fight and should lower the temperature on both sides. The first concerns the fine itself. After the Constitutional Council struck down the old 5 per cent proportional fine in decision 2016-554 QPC of 22 July 2016, the question arose whether the fixed fine survived. In its decision of 7 February 2018 (no. 402034), the Conseil d’État recorded the administration’s position that the proportional fine was no longer applied while «en revanche, l’amende fixe codifiée au premier alinéa du 2 du IV de l’article 1736 du CGI rest[ait] applicable» and it closed the case by ruling «La requête de M. B… est rejetée.» The lesson is direct: do not waste a challenge arguing that the whole penalty scheme collapsed with the proportional fine. The 1,500-euro fixed fine stands, so aim the challenge at the facts, the procedure and the proof instead. The second ruling concerns the gift presumption. On 17 September 2025, the commercial chamber of the Court of Cassation (appeal no. 23-10.403) upheld the L. 23 C and article 755 machinery against arguments based on legal certainty and free movement of capital, holding that «Les articles L. 23 C du livre des procédures fiscales et 755 du code général des impôts ne sont, dès lors, pas incompatibles avec le principe de sécurité juridique et le principe de libre circulation des capitaux, garanti à l’article 63 du TFUE» and it ended with the words «REJETTE le pourvoi.» Grand constitutional objections therefore fail; concrete paperwork wins.

B. Regularise and Contest: Corrective Return, Réclamation and the Tribunal in the Right Order

If no letter has arrived yet, regularise now. A spontaneous correction filed before any control or L. 23 C request changes the whole complexion of the file: the income is declared, the 3916 forms are lodged late but lodged, and the only remaining question is the penalty, argued from the position of a taxpayer who came forward rather than one who was caught. File a corrective return online covering each omitted year, attach one form 3916 per account with exact references, and pay the duties and interest shown. Then assemble the paper trail that answers the three questions every inspector asks: where the money came from, when the account existed, and what it earned. For origin, keep UK employment contracts and payslips, sale deeds for a British property, probate documents for an inheritance, and the bank statements showing the transfers into the account. For existence, keep opening letters, annual statements and closure confirmations, because the 3916 requires precise dates and the fine is argued per account and per year. For earnings, keep ISA annual summaries, dividend vouchers showing any UK withholding, and interest certificates. Where a dividend bore genuine UK withholding within the 15 per cent treaty cap, claim the French credit with the voucher attached; where UK withholding was taken on interest, reclaim it from HMRC and say so in the French file so the inspector does not treat the reclaimed sum as a second income.

If the fine or an assessment has already landed, challenge it in the strict order French procedure imposes. Start with the réclamation contentieuse, the written claim to the administration. Article L. 190 of the LPF defines its territory: «Les réclamations relatives aux impôts, contributions, droits, taxes, redevances, soultes et pénalités de toute nature, établis ou recouvrés par les agents de l’administration, relèvent de la juridiction contentieuse lorsqu’elles tendent à obtenir soit la réparation d’erreurs commises dans l’assiette ou le calcul des impositions, soit le bénéfice d’un droit résultant d’une disposition législative ou réglementaire.» Fines are expressly included, so the réclamation can attack the 1,500-euro penalty head-on: wrong account count, account outside the period, duplicate fine for a single account, declaration actually filed, or force majeure. Mind the clock. Article R*196-1 of the LPF requires most claims to reach the administration «au plus tard le 31 décembre de la deuxième année suivant celle» of the recovery or payment, and a late réclamation dies on admissibility before the merits are ever read. Send it by a traceable route, keep the receipt, and diary the administration’s six-month reply period: silence for six months is an implied refusal you can take to court.

The court is the tribunal administratif (administrative court) of your home address, and article R. 421-1 of the Administrative Justice Code sets the rhythm: «La juridiction ne peut être saisie que par voie de recours formé contre une décision, et ce, dans les deux mois à partir de la notification ou de la publication de la décision attaquée.» Two months from an express refusal, or from the implied refusal born of silence. For readers in Paris and the Île-de-France, the practical geography is simple: the local service des impôts des particuliers (SIP, the personal tax office) handles the return and the réclamation, the tribunal administratif de Paris hears Paris-based challenges at first instance, and appeals go to the cour administrative d’appel de Paris. Whatever the venue, the winning bundle looks the same: the filed 3916 forms, the bank proofs of origin and dates, the dividend vouchers, the HMRC reclaim correspondence for interest, and a short chronology showing spontaneous correction before any request where that is true. Ask the judge for discharge of the duties with interest where the treaty or the scale option supports it, reduction or discharge of the fine where the facts support it, and, where the gift presumption was applied, rebuttal with the origin documents, because article 755 presumes only «until proof to the contrary» and a documented transfer history is exactly that proof.

Conclusion

Your first French tax return as a British resident turns on three reflexes. Declare every UK account on its own form 3916, open or closed, earning or idle. Tax the ISA as France sees it, stream by stream, letting the treaty cap the British dividend tax at 15 per cent and reserve interest to France alone. And if a fine or a presumption arrives, answer with documents in the order the procedure demands: correction, réclamation, then the tribunal within its two months. The fixed fine survives grand challenges and the gift presumption has the highest court’s blessing, but both yield to precise facts proved on paper. This guide is written as the hub for the British newcomer’s tax file; keep it with your 3916 receipts, and let each later year be a routine copy of a file put right the first time.