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Ask a chatbot whether Lyon is in a zone tendue, or what notice period applies to your tenant, and you will get a confident answer — which may be quietly wrong. French administrative rules change by decree, by quarter and by commune, faster than any AI model's training data. In 2026 there is a better way: the Model Context Protocol (MCP) lets your assistant call real, maintained legal calculators instead of guessing. Here is what that means in practice, what you can already do free of charge, and where the limits are.

Every France–Switzerland frontalier who works from home now lives with two numbers: 40% and 49.9%. They look interchangeable. They are not. The 40% ceiling comes from the Franco-Swiss tax avenant signed on 27 June 2023 and decides which country taxes your salary from 1 January 2026. The 49.9% ceiling comes from the EU/EFTA social-security framework agreement in force since 1 July 2023 and decides which country's social system you contribute to. Two legal instruments, two reference bases, two sets of consequences — and one shared practical problem: you can only show you are under either line if you actually count your days. This guide is the counting how-to: what goes into each count, how mission days are treated, and a simple monthly method that holds up if anyone asks. It is general information drawn from official French, Swiss and EU sources — not personalised tax or legal advice — and for anything specific to your canton or contract it points you to the competent bodies.

If you own a French property and rent it out — or planned to start this summer — three sets of rules moved under your feet, and July 2026 is when they all become visible at once. The loi Le Meur tax split showed up for the first time in this spring's income declaration (it applies to 2025 income). The national registration teleservice for short-term lets came into force on 20 May 2026. And the DPE letting-ban calendar keeps tightening, now reaching tourist rentals too. This guide walks a non-resident or expat owner through what actually changed, what it costs to ignore, and what to check before the next tenant or guest arrives. It is general information, not legal or tax advice.

You've found a new flat, accepted a job in another city, or you're leaving France altogether — and now you need to give notice on your French rental. How long is the préavis? The honest answer is "it depends, precisely": three months by default for an unfurnished lease, one month for a furnished one, and one month for an unfurnished lease if your commune or your personal situation qualifies — under conditions most blog posts get subtly wrong. Get the reduced notice wrong and you owe up to two extra months of rent; get the delivery wrong and the clock never starts at all. This guide walks through the 2026 rules under art. 15 of loi n°89-462 as an expat tenant actually experiences them: which notice applies, the zone tendue list subtlety that trips up even French sites, when the countdown really begins, the exact end-date arithmetic, and how to claim the one-month notice without accidentally forfeiting it. This is general information, not personalised legal advice — verify your own case against the official sources linked throughout.

If you live in France and work for a Swiss employer, the days you spend working from your kitchen table are no longer a legal grey zone. Since 1 January 2026 a permanent framework governs how much you can telework from France before your tax situation moves. The headline number is 40%: up to 40% of your annual working time can be performed as telework from your home in France without changing the country that taxes your salary or costing you your frontalier status. This guide explains the 40% tax rule from the avenant signed on 27 June 2023 (published in France by [décret n° 2025-838](https://www.legifrance.gouv.fr/jorf/id/JORFTEXT000052129841)), the separate 49.9% social-security threshold that people constantly confuse with it, what happens if you cross either line, the new employer reporting duties, and how to plan a realistic telework week. Figures and dates are drawn from official French and Swiss sources — this is information, not personalised tax advice, so verify your own case before acting.

If you live in France and work in Switzerland, your children's family allowances are governed not by one country but by a European coordination rule that decides who pays first and who tops up. The result surprises many frontaliers: Swiss allowances are usually higher than French ones, so the money often flows the opposite way to what people expect. This guide explains the priority rule under [Article 68 of Regulation (EC) No 883/2004](https://www.cleiss.fr/docs/textes/883-04/t3-8.html), the Swiss allowance amounts canton by canton, when the French complément différentiel is actually paid by the CAF, what happens when both parents work in different countries, and the exact paperwork — your Swiss employer's caisse plus the CAF and the E411 form. Figures are 2026 values; treat them as information, not personalised advice, and confirm the current amounts with your canton's caisse and your CAF before you rely on them.