Filling in a tax return as a resident (taxation by assessment)

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Resident taxpayers liable for taxation (taxation by assessment) are required to report their income by filing a tax return (form 100).

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

In order to obtain the reimbursement of any excess tax withheld at source, employees or pensioners can - upon request - regularise their tax situation according to their personal situation:

  • either through taxation by assessment (form 100);
  • or by way of an annual adjustment (form 163 R).

If you download the PDF form, it is recommended that you save the form on your hard disk, then run Acrobat Reader and open the form using the Acrobat Reader application (go to file, then open) to avoid potential issues with how the form is displayed and how automatic calculations are performed.

Who is concerned?

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


The income tax return (form 100) must be submitted to the relevant tax office by 31 December of the year following the tax year in question, and the specific submission deadlines indicated by the different departments of the Luxembourg Inland Revenue (Administration des contributions directes - ACD) must be observed.

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

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.

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

The resident taxpayer must report their worldwide income (exempt and non-exempt income).

Exempt income is not taxable as such, but may be taken into account in determining the applicable tax rate for 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)

Rental income from a property located in a country with which Luxembourg has a double taxation agreement (tax-exempt income in Luxembourg): EUR 10,000.

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

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

Joint taxation

Depending on their situation (married, in a partnership or single, with or without children), taxpayers are taxed either jointly or individually.

Taxpayers who are taxed jointly only file a single tax return listing all of their income. 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

Taxpayers are liable for tax in Luxembourg on the income that they earn, which is subdivided into 8 categories:

  • business profit;
  • 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.

Taxable income is determined by adding together the different categories of net 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 deliver or send the completed and signed declaration to the competent tax office.

Even if the taxpayers have 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 their declaration:

  • 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.

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

Online services

Tax year 2023

Tax year 2022

Tax year 2021

Downloadable forms

Who to contact

Luxembourg Inland Revenue

Related procedures and links


Conditions under which resident taxpayers become subject to tax obligations in Luxembourg Adjustment of withholding tax on salaries by annual adjustment as a resident taxpayer Change in personal circumstances


Further information

Legal references

Loi modifiée du 4 décembre 1967

concernant l'impôt sur le revenu

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