Working in Luxembourg, living in France

The basic principle

The FR-LU bilateral tax convention (signed in 1958, most recently amended by the 2018 protocol and the 2023 avenant) follows the standard OECD model on employment income: tax is paid where the work is physically performed. For a French resident working in Luxembourg, that means the salary is taxed in Luxembourg, with the employer withholding the income tax via the standard retenue à la source. France, as the country of residence, retains the right to tax worldwide income — including the LU salary — but the convention grants a tax credit equal to the French tax that would have been due on the same income, which in practice neutralises the French liability.

The convention's 2023 avenant introduced (or, more precisely, formalised and updated) a tolerance: a French resident can perform up to a defined number of days of work physically in France without breaching the principle. Below the threshold, the entire salary remains taxable only in Luxembourg. Above it, the share of salary corresponding to the days worked outside Luxembourg becomes taxable in France instead. The current figure is 34 days per calendar year [verify], a substantial increase from the 19 and then 29 days under earlier versions.

The principle is straightforward; the counting is where it gets practical. The threshold is in days, not percentages, which makes it easier to track but harder to maximise — a teleworker doing one day a week from home approaches 50 days a year, well above the convention threshold even though their telework percentage stays comfortably under the EU 883/2004 social-security ceiling.

The 34-day threshold

"What counts as a day" is the question that determines whether your French tax bill is zero or non-zero. The administrative interpretation, broadly:

• A full day of work physically in France counts as one day outside Luxembourg.
• A partial day (e.g. you log in from France in the morning then drive to Luxembourg for the afternoon) is counted as a day — fractions do not exist in the convention text.
• Public holidays, annual leave, sickness do not count as working days for either side. They neither consume nor protect the threshold.
• Business trips to a third country (for instance, you fly to Germany for a client meeting) are not days in France.
• Working from a French airport or train on a stopover counts — the test is physical location during work, not the journey.

The threshold is annual and cumulative across all employers — if you change job mid-year, you do not get a fresh 34 days. The employer is not formally responsible for tracking your days, but most large Luxembourg employers now require a teleworking declaration as part of the remote-work agreement, and your own log is what the ACD and the French tax authority will request in case of audit.

Social security (883/2004 + framework agreement)

Social security and tax are governed by different rules and have different thresholds. Under EU regulation 883/2004, you are affiliated to the social-security system of the country where the work is physically performed (Luxembourg, via the CCSS), as long as you perform less than 25% of your activity in your country of residence. Above 25%, affiliation shifts to France, which means your employer would have to register with the URSSAF and pay French employer contributions on your salary — a material cost difference.

The multilateral framework agreement on telework, which took effect in 2023, raises this ceiling to up to 49.99% for participating countries on an opt-in basis. France is a signatory at the time of writing [verify current status]. Importantly, the framework agreement applies only to telework — work performed remotely using digital tools — and not to physical attendance at a French office or client site. It is also opt-in: you (or your employer, on your behalf) must request it via the CCSS or the URSSAF.

Because the tax convention sets a day-count and the social-security framework sets a percentage, the two can run in opposite directions. A French cross-border worker could be safely under the 34-day convention threshold yet over the 49.99% social-security ceiling if their pattern is heavily weighted to remote days early in the year, or vice versa. The two figures should be tracked separately.

Train lines and travel times

Most French cross-border workers commute by train, by car-then-train at a P+R, or directly by car. The main lines into Luxembourg-Gare:

• Thionville–Luxembourg — the workhorse of the French commute. TER and CFL services run at peak frequency every 10–15 minutes, with travel time around 20 minutes city-to-city. Thionville itself is a 5-minute drive from the A31, which feeds the LU-bound CR152 and A3.
• Metz–Luxembourg — direct TER and CFL service, around 45 minutes, hourly off-peak and every 30 minutes at peak. Metz is the most populous catchment in the corridor and the train option for those further from the border.
• Nancy–Luxembourg — around 90 minutes, less frequent. Some commuters drive to Thionville and pick up the train; others use the direct service for the occasional office day.
• Longwy–Luxembourg — the western corridor, via Athus and the Belgian network. Useful for residents of the Meurthe-et-Moselle north.

Tickets across the FR-LU border require a combined SNCF/CFL tariff; pure-Luxembourg travel is free at point of use since March 2020, but the cross-border leg is not. The Flexpass and monthly subscription products from SNCF cover the French side; the CFL part is covered as part of the cross-border ticket if bought on a combined basis. Some employers reimburse a portion of the commute under the mobilité durable employer scheme.

Filing in France (formulaire 2042 + 2047)

French residents file an annual income-tax return regardless of whether they owe French tax. The forms relevant to a Luxembourg cross-border worker:

• Formulaire 2042 — the main household declaration. The Luxembourg salary is not entered as a French salary; instead, it is reported via the annexe.
• Formulaire 2047 — the annexe for foreign income. The Luxembourg gross salary is declared here, with the country code "LU" and the type of income (salaires). The form generates a tax credit equal to the French tax that would have been due on that income, eliminating the French tax bill on the LU-source portion.
• Cases to watch: if you exceed the 34-day threshold, the portion of salary corresponding to days worked in France is reported as a normal French salary (taxable in France) — the convention's credit no longer applies to that share.

The French tax administration learns of Luxembourg income via the automatic information exchange between EU member states; the declaration is the formal step that produces the credit and resolves the file. The same return also handles your spouse's French income, French rental income, capital gains and any other household items; the LU salary feeds into the revenu fiscal de référence used for means-tested benefits, taxe d'habitation legacy items and certain commune-level decisions.

CFE, CAF and family allowances

Family allowances follow their own EU coordination rules. Under regulation 883/2004, when one parent works in Luxembourg, Luxembourg is the country of primary competence for family benefits regardless of residence. The Caisse pour l'avenir des enfants (CAE) pays the LU family allowance. The French CAF (Caisse d'allocations familiales) plays a secondary role: it pays the differential if the French allocation would have been higher than the Luxembourg one. For most household configurations the LU benefit is higher and the differential is zero — but the file still has to be opened with the CAF, which is where the paperwork frustration lives.

For taxe d'habitation (now mostly abolished on principal residences but still applicable in some cases) and other commune-level French taxes, the LU salary feeds the revenu fiscal de référence and can therefore affect the amount due. The same applies to commune-level CFE (Cotisation foncière des entreprises) if you have any self-employed activity on the French side.

Edge cases

Several common configurations sit outside the standard "employed in Luxembourg, resident in France" picture:

• One spouse in Luxembourg, one in France: each spouse is taxed in the country of employment; the household declaration in France includes both salaries (LU one on 2047, FR one as normal). Joint filing in Luxembourg under tax class 2 requires the assimilation conditions to be met (broadly, at least 90% of household worldwide income taxed in Luxembourg) — often not the case when one spouse earns in France.
• Freelancers and indépendants: different framework entirely. A French resident operating as an indépendant for a Luxembourg client is generally taxed in France (where the activity is performed) unless they have a permanent establishment in Luxembourg. Social security follows the same logic — affiliation in France via URSSAF unless a specific A1 certificate routes them through CCSS.
• Seasonal or short-term work: the day-count is annual; a six-month assignment that ends mid-year still uses the 34-day allowance pro-rated against the period worked, although the convention text does not pro-rate explicitly. Practitioners apply common sense; the ACD does not penalise good-faith pro-rating.
• Mid-year move into Luxembourg: you become a Luxembourg tax resident from the date of commune registration. The French declaration covers the pre-move part of the year; the Luxembourg declaration covers the post-move part. The day-count threshold applies only to the cross-border period.

How to register as a cross-border worker from France

The practical sequence:

1. Sign the Luxembourg contract. CDI or CDD, with the remote-work clause (if any) explicitly written. The number of days teleworked from France drives both the convention day-count and the social-security percentage.
2. Affiliation to the CCSS via the employer. The employer declares the hire to the Centre commun de la sécurité sociale, which issues your matricule. You receive the CCSS welcome pack with the affiliation reference.
3. Request the S1 form from the CNS. This is the EU form (formerly E106) that coordinates your LU CNS cover with your French CPAM. Submit it to your CPAM de rattachement; from that point you stay registered with a French GP and use the carte Vitale for in-France care, with reimbursement coordinated between the two systems.
4. Open a French file with the CAF (if you have children) — even if the differential turns out to be zero, the file is required and the LU allowance is paid via the CAE in Luxembourg as the primary-competence body.
5. Declare in France annually: formulaire 2042 + annexe 2047. The first year is the most painful; subsequent years are autoremplis (pre-filled) and faster.

A worked example, in qualitative terms

Consider a hire on a Luxembourg CDI at salary level N, resident in Thionville, working 2 days a week from home from January. By June, days worked in France approach 50, well above the 34-day convention threshold but still under the 49.99% social-security ceiling. The tax consequence: the share of salary corresponding to days worked in France (around one-fifth of working days, after factoring in leave and public holidays) becomes taxable in France instead of Luxembourg. The LU payroll continues to withhold tax at source on the LU-day share; France taxes the FR-day share. The household 2042 reports both: the LU portion still produces a tax credit, the FR portion is taxed at French progressive rates. The social-security side is unaffected — still CCSS, still CNS — because the percentage stayed under the framework agreement's ceiling. The practical effect on net pay: the French tax bill on one-fifth of salary at French marginal rates, less than it sounds, but enough to make many cross-border workers either negotiate fewer remote days or accept the trade-off explicitly.

If you live in France and work in Luxembourg

Topic	Where it lands
Income tax on LU salary	Luxembourg, withheld at source by the employer
Social security	Luxembourg (CCSS) if France-based work < 25% / < 49.99% under telework framework
Family benefits (one parent in LU)	Luxembourg CAE primary; French CAF differential (often zero)
Remote-work threshold for full LU taxation	34 days per calendar year [verify against 2023 avenant]
French filing obligation	Mandatory: formulaire 2042 + annexe 2047, even if no FR tax due
Healthcare	CNS-insured, S1 form to French CPAM, French GP + carte Vitale for in-France care

What this means in practice

Three concrete steps for a French resident starting a Luxembourg job:

1. Negotiate the remote-work clause carefully. Two days a week from home already exceeds the convention threshold. If the role is genuinely remote-heavy, work the tax cost into the salary expectation and document the agreement in writing.
2. Set up a day-tracking habit from week one. A simple spreadsheet with one row per working day and the country code is enough. Both tax authorities can audit; the burden of proof is on you.
3. Open the CAF file even if you expect zero differential. The file has to exist; CAF processing times are long; opening it on arrival removes a friction point if your situation later changes (additional child, French spouse joining the LU workforce, etc.).

Frequently asked questions