Filling a tax return as a non-resident (taxation by assessment)

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Non-resident taxpayers who are subject to taxation in Luxembourg (taxation by assessment) are required to report their income by filing a tax return (form 100).

Under certain specific conditions of eligibility, this tax return can be completed and submitted electronically via

Regardless of their address, natural persons are in principle considered to be non-resident taxpayers in Luxembourg if they possess a centre of vital interests abroad, outside Luxembourg.

Even if they are not subject to tax liability, non-resident taxpayers can decide to file a tax return in order to regularise their withholding tax situation. In some cases, non-resident taxpayers may submit an annual adjustment form in place of the tax return.

In order to prevent the risk of computation and display problems, the Luxembourg Inland Revenue (Administration des contributions directes) recommends that taxpayers who download the PDF form should first save the form to their hard drive, then launch Acrobat Reader (version 10, 11, or Acrobat Pro) and then open the form using the Acrobat Reader menu (File > Open).

Who is concerned?

Individuals who are required to file a tax return or who wish to file a tax return to regularise their withholding tax situation must do so using form 100.


The income tax return (form 100) is to be submitted to the competent tax office (depending on the place of residence of the taxpayer).

It must be submitted by 31 December of the year following the tax year.

Example: for tax year N, the tax return is due by 31 December of year N+1.

In some cases, specific deadlines apply. These deadlines are communicated by the Luxembourg Inland Revenue (ACD) by mail.

Persons who require an extension of the deadline for submitting or filing the tax return should apply for the extension (preferably by fax or post) to the competent tax office.

Competent tax offices for non-resident taxpayers:

  • the Luxembourg Y tax office has jurisdiction over taxpayers whose tax residence is in France;
  • the Luxembourg Z tax office has jurisdiction over taxpayers whose tax residence is in Germany;
  • the Luxembourg X tax office has jurisdiction over non-resident taxpayers whose tax residence is in Belgium or another country (with the exception of Germany or France).

In the event of failure to meet the indicated deadlines, an additional tax, a late payment fee or a coercive penalty may be levied by the tax office.

Taxpayers who refuse to file their tax return will force the tax office to determine the tax liability using the estimated assessment procedure (taxation d'office par voie d'estimation).

How to proceed

General principles of taxation

Non-resident taxpayers who are taxable in Luxembourg can opt to be treated as Luxembourg residents for tax purposes, i.e. they choose to be treated as a taxpayer residing in Luxembourg.

They will then be entitled to the same tax deductions and tax credits available to resident taxpayers.

If a non-resident taxpayer chooses not to take up this option, they will be liable for tax only on their income from Luxembourg sources. In that case, only a limited number of expenses are tax deductible.

Non-resident taxpayers who opt to be treated as Luxembourg residents for tax purposes must report both their exempt and their non-exempt income (e.g., income received from the rental of a property located in Belgium, the salary of a spouse employed in France, etc.) in their tax return.

In this case, the foreign exempt income is not taxable as such, but is taken into account in determining the applicable tax rate for the non-exempt taxable income.

Simple example illustrating the case of a single (unmarried) taxpayer (tax class 1):

Taxable income in Luxembourg (salary): EUR 40.000 (indigenous income = income from Luxembourg source)

Income from paid employment originating in a third country with which Luxembourg has a tax treaty against double taxation (exempt income in Luxembourg): EUR 10,000.

The total taxable income taken into account to calculate the tax rate is 40,000 + 10,000 = EUR 50,000.

According to the 2017 income tax scale, the tax due for an income of EUR 50,000 (tax class 1) amounts to EUR 9,106. Thus, the overall tax rate is 9,106 / 50,000 = 18.21 %. To this tax rate is added the 7% contribution to the employment fund, which brings the applicable rate to 19.48%.

This rate is applied only to non-exempt income, i.e., in this case, to the EUR 40,000.

Tax due on taxable income in Luxembourg, based on the tax scale: 40,000 × 19.48 % = EUR 7,792.

Joint taxation

Taxpayers, depending on their situation (married, in a partnership or single, with or without children, treated as resident taxpayers), are taxed either jointly or individually.

Non-resident taxpayers who are taxed jointly must file a single tax return for all of their domestic income taxable in Luxembourg. The tax is determined on the basis of the taxpayers' aggregate joint net income, and is payable by them as a unit.

Determination of taxable income

Non-resident taxpayers, whether they are treated as resident taxpayers or not, are taxed in Luxembourg only on the income they earn in Luxembourg (i.e., their domestic income). That income is subdivided into 8 categories:

  • business profits;
  • agricultural and forestry profits;
  • earnings from self-employment;
  • net income from paid employment;
  • net income from pensions or annuities;
  • net investment income;
  • net rental property income;
  • and net miscellaneous income.

The taxable income is determined by the sum of the net domestic income, after deduction of:

For non-resident taxpayers who have opted to be treated as residents for tax purposes, the tax rate is determined by adding together the different categories of net domestic income, and deducting special expenses such as:

Income subject to tax (taxable income) is equal to the income deferred at the end of the tax form, minus certain deductions (e.g.: allowance for extraordinary expenses borne by the taxpayer).

This adjusted taxable income is then matched against the income brackets in a progressive income tax scale.

Submission of the tax return

In principle, each February, taxpayers should receive:

  • either an invitation to download and electronically complete the tax return forms provided on or on the website of the Luxembourg Inland Revenue (ACD);
  • or a paper form (form 100) by mail.

The declarant shall submit in person or send the completed and signed declaration to the competent tax office.

Even if the taxpayer has received a paper form, they can complete the tax return electronically and send it to the ACD via, along with the various supporting documents.

Please note that the use of the electronic assistant to complete the tax return via is subject to specific conditions of eligibility.

The declarant must attach certain supporting documents to his tax return:

  • a compensation certificate (annual salary statement) and/or annual pension statement;
  • a certificate showing the amount of interest paid on a mortgage or personal loan taken out during the tax year in question (annual financial statements);
  • a civil partnership certificate when joint taxation is requested for the first time for the tax year in question.

Declarants must also include:

  • all supporting documents which substantiate their personal situation or any other information provided in the declaration;
  • proof of income they receive in their country of residence.

The Luxembourg Inland Revenue reserves the right to request additional supporting documents as part of the process of verifying any information, statements, applications, declarations, claims or appeals submitted to its offices.

In the event of an oversight or an error in the tax return—regardless of whether the return is sent by post or electronically—taxpayers should contact the competent tax office.

Any request for correction must necessarily be communicated in writing to the competent tax office within 3 months of the taxpayer sending the declaration.

Setting the amount of tax payable

The income tax payable by the taxpayer is determined by matching the rounded-off adjusted taxable income against the income brackets in a progressive tax scale.

Owing to the progressive nature of the scale, taxpayers with higher income pay proportionally more tax than taxpayers with lower income.

Online services and forms

Who to contact

Luxembourg Inland Revenue

Related procedures and links

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