How to file your income tax return in Luxembourg

Luxembourg taxes most employment income at source through the tax card, so not everyone has to file a return. But a large group of residents and cross-border workers are required to complete the income tax return for individuals, known as the modèle 100 form. Here is how the process works in 2026.

Who must file the modèle 100

You are subject to taxation by assessment, and therefore obliged to file, in several situations. As a resident you must file if your taxable income exceeds 100,000 euros, if you receive net income not subject to withholding of more than 600 euros (for example rents or foreign income), or if you hold several salaries or pensions whose combined amount tops 36,000 euros (tax classes 1 or 2) or 30,000 euros (tax class 1a). Where the trigger is non-withheld income above 600 euros, there is no lower threshold below which you are exempt from filing.

Non-residents with Luxembourg-source salary above 100,000 euros are also required to file. Other non-residents may opt in to be taxed as residents (tax assimilation) to claim deductions, provided at least 90% of their worldwide income is taxable in Luxembourg, or their income taxable abroad stays under 13,000 euros.

If none of these conditions apply and you are simply an employee or pensioner, you usually do not need a full return. Instead you can ask for an annual adjustment (see below). For the rules on who falls into each tax class, see our explainer on [Luxembourg tax classes](/en/finance/luxembourg-tax-classes), which is distinct from the [tax card](/en/finance/luxembourg-tax-card) that drives monthly withholding.

The deadline and the forms

The forms appear at the beginning of the second quarter of the year following the income year. For the 2025 tax year, the filing window runs from 7 April 2026 to 31 December 2026. The general rule is that a return is due by 31 December of the year following the tax year.

The core document is the modèle 100 (form 100 F in French, 100 D in German), published each year by the Administration des contributions directes (ACD).

Filing electronically or on paper

You have two routes:

• Online via MyGuichet.lu — use the electronic assistant, which pre-fills the form and guides you through each section, or upload a completed and signed PDF. Both require authentication with a LuxTrust product or an electronic eID card.
• On paper — print the modèle 100, sign it and post it to your competent tax office.

Resident and non-resident taxpayers who are eligible can submit the full return online via MyGuichet.lu.

Common deductions to claim

Filing lets you reduce your taxable base. Frequently used deductions include:

• Mortgage and consumer loan interest
• Insurance premiums and supplementary pension contributions
• Commuting costs (the kilometric allowance)
• Childcare and domestic help costs
• Gifts and donations to recognised bodies

Non-residents only access most of these if they opt for resident treatment.

What happens after you file

The tax office reviews your return and issues a tax assessment (bulletin d'impôt) stating your final liability. If too much was withheld during the year, you receive a refund; if too little, you pay the balance. The assessment also tells you whether advance payments will be set for future years.

If you do not have to file but only want a refund of over-withheld tax, request an annual adjustment using form 163 R. This procedure cannot in principle increase your tax bill and is also due by 31 December of the following year. Note that if you claim deductible loan interest tied to a property, you must use the modèle 100 instead.

Last reviewed: June 2026, based on guichet.public.lu and the Administration des contributions directes.