Guides

Precise answers to the most common tax and administrative questions, in France, Luxembourg, and Belgium.

• Install CtrlC-CtrlV as an app on your phone (iPhone and Android) — Two taps are enough to add CtrlC-CtrlV to your home screen: the site then opens full-screen, with its own icon, like a real app — no app store, no download, no account.
• Luxembourg cross-border worker tax class: how does it work? — Class 1, 1a, or 2: what determines your tax class as a French or Belgian cross-border worker, and why a couple isn’t always in class 2.
• Gross remuneration or withholding calculation basis: which figure to declare? — The Luxembourg salary certificate shows two similar-looking amounts. Here’s which one to use on your tax return.
• Social contributions and tax credit (CIS) on the Luxembourg certificate: are they deductible? — The Luxembourg salary certificate lists social contributions and an employee tax credit. Here’s what to do with them on your return.
• Belgian cross-border worker in Luxembourg: the 34-day telework threshold — Beyond 34 days of telework per year from Belgium, part of your Luxembourg salary becomes taxable in Belgium. How it works and how to plan for it.
• Micro-foncier or déficit foncier: which regime for your French rental income? — Two different regimes for declaring unfurnished rental income in France, with a threshold that makes the choice automatic in some cases.
• PER, donation, rental property, or PEA: comparing tax-optimization levers — Four ways to reduce your French tax bill work very differently and suit different timelines. Here’s how they compare before you choose.
• Internship, apprenticeship, student job: what’s tax-exempt (and up to how much) — Internship pay, apprentice salary, student jobs: the exact exemption caps for 2025 income in France, Luxembourg, Belgium, and Germany — and the prefilled-amount trap.
• Box 8TK: the tax credit on foreign income, explained simply — Box 8TK (form 2042 C) takes the total of your foreign-source income already taxed abroad that qualifies for a tax credit equal to the French tax: you pay no French tax on it, but it counts for the rate applied to your other income.
• Box 1AF: where to declare a foreign salary (and how not to confuse it with 1AJ, 1AC or 1AG) — Box 1AF of the 2042 takes filer 1’s foreign-source salaries that qualify for a credit equal to French tax (1BF for filer 2). It’s filled via annex 2047, and its total carries over to box 8TK.
• Form 2047: the mandatory form for foreign income — The 2047 is the 2042’s annex for any foreign-source income: cross-border salaries, foreign pensions, dividends or interest from foreign accounts. You detail each income there, then carry the totals to the matching boxes of the 2042.
• Form 3916: declaring a foreign account (N26, Revolut, cross-border account…) — One form 3916 per account held, opened, used or closed abroad during the year — bank account, life insurance or securities account, even inactive. Forgetting costs a €1,500 fine per account. Crypto has its variant: the 3916-bis per foreign platform.
• Box 2OP: tick it or not? Flat tax vs scale, the real math — By default, your dividends and interest face the flat tax (12.8% income tax + 17.2% social levies). Ticking box 2OP switches them to the progressive scale: a win if your bracket is 0% (you save 12.8% of the amount) and often at 11%, a loss at 30% and above.
• Form 2042: the complete guide (annexes, dates, pitfalls) — The 2042 is THE French income tax return: salaries, family, tax reductions. Prefilled data covers the basics, but the money-saving boxes (actual expenses, donations, PER, 2OP) and the annexes (2042 C, 2047, 3916) are up to you.
• Luxembourg form 100: who must file it, and how to fill it box by box — Form 100 is the Luxembourg tax return, for residents and cross-border workers alike. Generous deadline: December 31 of the following year. Even when not mandatory, filing often recovers withheld tax through deductions (insurance, pension savings, interest…).
• French reference tax income (RFR): where to find it and why it matters so much — The RFR appears on the first page of your French tax assessment. It isn’t your taxable income: it adds back certain exempt income (overtime, foreign income under tax credit…) and acts as the gateway to many benefits, exemptions and reduced rates.
• ASDIR: the instant French tax proof (no need to wait for the summer assessment) — The ASDIR is issued immediately after you submit your online French return. It shows your income and reference tax income, and works as proof for landlords, banks and administrations while you wait for the final assessment.
• Tax-on-web: filing your Belgian IPP online without picking the wrong code — Tax-on-web (via MyMinfin) is Belgium’s online personal income tax filing service. In 2026: paper by June 30, online by July 15. Every amount goes behind a four-digit code — and several benefits depend on your region.