Last updated:
French & Swiss Tax Obligations for CERN Employees
CERN salary is exempt from national income tax, but you may still need to file a declaration. Always consult a tax professional for your specific situation.
CERN Internal Tax
CERN levies its own internal tax on staff salaries, deducted directly from your monthly pay slip and administered entirely by the organisation. It has nothing to do with French or Swiss national taxes and is separate from any obligations you may have in either country.
Under the Protocol on Privileges and Immunities of international organisations, CERN staff salaries are exempt from national income tax in both France and Switzerland. The exemption covers your CERN remuneration only. Any income earned outside CERN -- rental income, investment returns, freelance work -- remains fully taxable in your country of residence under the applicable national rules.
French Tax Obligations (Pays de Gex Residents)
If you live in France, you must file an annual tax declaration (declaration de revenus), even if you have zero taxable income from CERN. Your CERN salary is declared as exempt income, but the French tax authorities still require the filing.
Any outside income -- from rental property, investments, dividends, or freelance work -- must be declared and is taxed at standard French rates. Be aware that the taux effectif rule may apply: your exempt CERN salary can be used to calculate the effective tax rate on your other income, potentially increasing the marginal rate.
The declaration is filed online at impots.gouv.fr, typically by the May or June deadline depending on your department. If you are a new resident, you must first register at the local Service des Impots des Particuliers (SIP) in your area to obtain a tax number (numero fiscal) before you can file online.
Swiss Tax Obligations (Geneva Residents)
If you live in the Canton of Geneva or elsewhere in Switzerland, you must file a cantonal and federal tax return each year. Your CERN salary is declared on the return but marked as exempt. Any outside income -- rental property, investments, self-employment -- is subject to both cantonal and federal tax.
Geneva has among the highest cantonal tax rates in Switzerland, so outside income can be taxed at a significant rate. You can file your return online using the GeTax software or through the e-demarches platform provided by the Canton of Geneva. The filing deadline is typically 31 March, though extensions can be requested.
Double Taxation Treaties
France and Switzerland have a bilateral double taxation treaty that determines which country may tax specific types of income. Cross-border workers (frontaliers) are subject to particular rules under this agreement.
That said, CERN staff are generally not considered frontaliers under the treaty, because their income comes from an international organisation rather than a Swiss or French employer. If you earn income in both France and Switzerland outside of CERN, it is worth reviewing the treaty provisions to understand how that income is allocated and taxed. A cross-border tax advisor can help you sort out the details.
Practical Tips
It is worth keeping detailed records of all outside income -- bank statements, rental contracts, investment reports -- well before filing season arrives. If you have income in both France and Switzerland, or your personal situation is at all complex, a cross-border tax advisor (fiscaliste transfrontalier) can save you considerable trouble. You should also request an attestation from CERN HR confirming your employment status and salary exemption, since tax authorities on both sides of the border may ask for it.
Filing deadlines differ between the two countries: France typically requires declarations by May or June, while Switzerland sets its deadline on 31 March (though extensions are available). Whatever your situation, do not skip the filing -- even when your CERN salary is fully exempt, failing to submit a declaration can lead to penalties or unnecessary complications with the tax authorities.