4. Identification and personal information

A tax return in Luxembourg always begins with a precise and complete identification of the taxpayer. This personal information is essential for the Tax Authorities (Administration des Contributions directes) to correctly process your tax file. Incorrect or missing information can cause delays or even errors in the calculation of your tax liability.

Luxembourg tax file number

The tax file number (numéro de dossier) is an individual 11-digit identifier, in the format xxxx 01xx xxx, assigned by the Administration des Contributions Directes (ACD) to every taxable person in Luxembourg, whether resident or non-resident. It appears on the tax card, and all official correspondence from the administration.

Taxpayers subject to joint taxation (married couples or registered partners) also receive a common 11-digit file number, in the format xxxx 00xx xxx. This number is used for the same types of taxes as those associated with individual numbers.

Tax identification number (TIN) for neighboring countries

For cross-border workers, the NIF from their country of residence is also required in the Luxembourg tax return.

France

In France, the 13-digit tax number (format: 99 99 999 999 999) is assigned by the tax administration. It can be found on:

• Your tax notice (income tax, housing tax, property tax)
• Your pre-filled income tax return
• Your personal account on the tax authority’s website

Belgium

In Belgium, the tax identification number is the national register number (NISS) for residents or the BIS number for non-residents. It can be found on:

• Your Belgian identity card
• Your electronic identity card (eID)
• Your SIS card (for social security)
• Your tax notice or payslip

Germany

In Germany, the tax identification number (Steuer-ID or IdNr.) is automatically assigned after registration at the Bürgeramt (citizens’ office). It can be found on:

• Your German identity card
• Your tax notice
• Your payslip

Tax identification number for other countries

For all other countries, the NIF is generally indicated on official tax documents, such as income tax returns, tax notices, or tax cards issued by the local tax authority.

Contact details and additional personal information

It is essential that you provide up-to-date and accurate information on your tax return.

This includes, for example:

• Full postal address: to receive all official correspondence and notifications from the ACD.
• Email address and telephone number: to facilitate rapid contact in the event of questions or errors in your return.
• Marital status: single, married, registered partner, widowed, etc. Your marital status affects the calculation of your tax and your eligibility for certain allowances.
• Occupation and main activity: indicate your current occupation and the type of activity you carry out.
• Bank details (IBAN/RIB): required for the payment of any tax refund directly into your account.