The income tax return for natural persons (taxation by assessment)
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Taxpayers subject to taxation by assessment must report their income by filing an income tax return for natural persons (form 100).
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:
- by assessment (form 100); or
- or by way of annual adjustment (form 163 R).
Subject to certain specific eligibility conditions, you can settle the tax by means of an assessment via the electronic assistant on the secure MyGuichet.lu platform. You can fill in your income tax return using the online assistant. If you cannot use the online assistant, you can file your income tax return by sending in 'form 100' (to be downloaded under 'Online services and forms' below or from the ACD website):
- electronically via the MyGuichet.lu procedure for PDF submissions; or
- by post to the relevant tax office.
If you decide to use the PDF form, please follow the instructions carefully to avoid calculation and display problems. You can find more information on this subject in our help article.
Who is concerned
You will find detailed information on persons subject to taxation by assessment on the website of the Luxembourg Inland Revenue (ACD).
Deadlines
Regardless of how you file your tax return (electronically or by post), you must submit it by 31 December of the year following the tax year in question at the latest.
Example: for tax year N, the tax return is due by 31 December of year N+1 at the latest.
For the 2024 tax year, the tax return submission period therefore runs from 7 April 2025 to 31 December 2025.
You must always respect the specific deadlines for correspondence sent by the various ACD departments. In the event of failure to comply with the stated deadlines, the tax office may apply:
- supplementary taxes;
- late payment interest; or
- a penalty payment.
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
- Residents
- Non-residents
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.
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%. This tax rate is increased by the 7% contribution to the employment fund, bringing 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
Depending on their situation (married taxpayers, partners or single taxpayers, with or without children), taxpayers are taxed either jointly or individually.
- Residents
- Non-residents
Taxpayers who are taxed jointly only file a single tax return listing all of their income.
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
- Residents
- Non-residents
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:
- allowances paid to a divorced spouse or other permanent allowances;
- interest payments on consumer loans used to finance the purchase of a car, movable assets, etc. (note that interest in connection with existing buildings or those under construction are not considered as special expenses, and must be reported on sheet L, form 100);
- insurance contributions and premiums;
- contributions to supplementary pension schemes (LRCP);
- gifts or donations.
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:
- the minimum flat-rate;
- the mandatory social contributions;
- supplementary pension insurance premiums (LRCP).
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:
- allowances paid to a divorced spouse or other permanent allowances;
- interest payments on consumer loans used to finance the purchase of a car, movable assets, etc. (note that interests paid in connection with existing buildings or those under construction are not considered as special expenses, and must be reported on sheet L, form 100);
- voluntary and private insurance premiums and payments;
- gifts and donations, etc.
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, you will receive the following at the beginning of the second quarter of the current year:
- an invitation to download and complete the tax declaration forms available on this page under 'Online services and forms' or on the ACD website;
- or a paper form (form 100) by post; or
- a simple pre-filled tax return.
In 2025, only taxpayers who just have to declare income from 'salaries and pensions' in the absence of any deductions other than the minimum flat-rate deduction received a letter at the beginning of March offering them the option of opting for the simple tax return. If they agree, they will receive a pre-filled proposal for the simple tax return at the beginning of May, which they will need to check and validate.
You must submit your completed and signed tax return:
- electronically via the MyGuichet.lu procedure for PDF submissions; or
- by post to the relevant tax office.
Even if you have received a paper form, you can fill it in on your computer and send it, together with the attachments, to the ACD via the MyGuichet.lu procedure for PDF submissions.
If you wish to complete your tax return using the electronic assistant, please consult our explanatory information page on this subject to find out if you belong to the target audience.
Attachments
- Residents
- Non-residents
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.
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.
In our tutorial, we use screenshots to explain, step-by-step, the different ways of adding attachments to a procedure with authentication.
The Luxembourg Inland Revenue (ACD) 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.
Omission or error
In the event of an oversight or an error in the tax return—regardless of whether the return is sent by post or electronically—you should contact the competent tax office.
You must send any request for correction in writing to the competent tax office no later than 3 months after submitting your tax return.
Setting the amount of tax payable
The income tax payable 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
-
Contact Centre - Luxembourg Inland Revenue (ACD)
- Address:
- 33, rue de Gasperich L-5826 Hesperange Luxembourg
Related procedures and links
Procedures
Links
Further information
-
Imposition par voie d'assiette (impôt sur le revenu)
sur le site de l'Administration des contributions directes
-
Calcul d'une rémunération mensuelle nette
sur le site de l’Administration des contributions directes (ACD)
-
Mémento fiscal - Résumé des impôts directs perçus
sur le site de l’Administration des contributions directes (ACD)
-
Barèmes
sur le site de l’Administration des contributions directes (ACD)
-
Calculatrice fiscale
sur le site du ministère des Finances
-
Délais
sur le site de l'Administration des contributions directes (ACD)
Legal references
concernant l'impôt sur le revenu
