3. Tax returns in Luxembourg

Obligation to file a tax return in Luxembourg

You are required to file a Luxembourg tax return in several specific situations.

Resident taxpayers

A resident must file a tax return if:

• The taxable income exceeds 100.000€.
• Net income not subject to withholding tax exceeds 600€.
• Remunerations exempt from withholding tax are received.
• An additional tax card is held, with taxable income > 36.000€ (classes 1 or 2) or > 30.000€ (class 1a).
• Net income exceeding 1.500€ is subject to withholding on investment income.
• Net income exceeding 1.500€ is subject to withholding on directors’ fees.
• The taxpayer is married and wishes to opt for joint taxation with a non-resident spouse, if the resident earns at least 90% of the household’s professional income.
• The taxpayer is in a civil partnership (PACS) and wishes to opt for joint taxation or individual taxation with income reallocation.
• The taxpayer is married and wishes to opt for full individual taxation or individual taxation with income reallocation.
• Income from assets or certain pensions subject to long-term care insurance contributions is received.
• Only income not subject to withholding tax (investment income, directors’ fees) is received and taxable income exceeds 12.438€.

Non-resident taxpayers

A non-resident must file a tax return if:

• Taxable income exceeds 100.000€, or an additional tax card is held (above 36.000 € for classes 1 or 2, and above 30.000€ for class 1a).
• Net income exceeding 1.500€ subject to withholding on investment income is received.
• Net income exceeding 1.500€ subject to withholding on directors’ fees is received.
• The taxpayer wishes to be assimilated to a resident taxpayer.
• The taxpayer is in a civil partnership (PACS) and wishes to opt for joint taxation or individual taxation with income reallocation.
• The taxpayer is married and wishes to opt for full individual taxation or individual taxation with income reallocation.
• The tax administration requires it.

Voluntary declaration and its advantages

Even if you are not required to file a tax return, it can be beneficial in certain situations:

1. To get money back through tax deductions

If you have incurred deductible expenses, such as:

• Insurance premiums (civil liability, health, life…),
• Contributions to a home savings plan or a old-age pension plan,
• Donations to recognised non-profit organisations,
• Childcare expenses or domestic staff expenses,
• Interest on a mortgage loan for your main residence.

2. To correct excessive withholding at source

If you have paid too much tax during the year, a voluntary tax return allows you to recover the excess amount.

Does the tax return have to be submitted every year?

Taxpayers who are legally required to declare their income must do so every year. Those who are not required to do so may choose not to file a return. If they do so voluntarily, for example to obtain a tax benefit, they are included in the “regular” taxpayer base, without distinction by the tax authorities. To stop filing a non-mandatory return, simply notify the authorities.

The tax return (Déclaration d'impôt)

Form 100 is the standard tax return for individuals in Luxembourg. It allows you to declare all income received during the year, whether from salaries, pensions, investment income, directors’ fees, rental income, or investments.

The annual adjustment (Décompte annuel)

Even if you are not legally required to file a tax return, it can be advantageous to request an annual adjustment by filing Form 163. This simplified form allows you to check whether the monthly withholding taxes actually correspond to the amount of tax due, and to recover any overpayments.

When to use Form 163?

Form 163 is particularly suitable in the following situations:

• Starting a career mid-year: if you began working in Luxembourg during the year, the total withholding may not reflect your actual income.
• Periods of variable or no remuneration: unemployment or other income interruptions.
• Non-resident employees: if you worked in Luxembourg for less than 9 consecutive months.

Form 163 must be sent by post to your competent RTS office.

How to submit my tax return in Luxembourg

Your tax return must be received by your tax office no later than December 31.

You must send either form 100 or form 163, but not both.

Form 100

For form 100, there are two options. The first is to submit it online via MyGuichet.lu. Simply log in to your account and upload the form along with the annexes. This option is only valid for form 100. The second option is submission by postal mail. In this case, print the PDF, sign on the last page after checking all the information, and send it to your tax office. The address is located on the first page, at the top left.

Form 163

For form 163, the only option is submission by postal mail. Print the PDF, sign on the last page after verifying the information, and send it along with the annexes to your RTS office, whose address is on the first page, at the top left.

Deadlines for filing tax returns

The declaration must be filed no later than 31 December of the year following that in which the income was earned.

For the 2024 tax return, the filing deadline is 31 December 2025.