Personal income tax return in Luxembourg: who has to file

In short. In Luxembourg, a resident has to file an income tax return, form 100, notably when taxable income exceeds 100,000 €, when several salaries or pensions subject to withholding are drawn at the same time, or when more than 600 € a year of income not withheld at source is received. Outside those cases, an employee is usually not required to file, but often has an interest in requesting an annual adjustment (form 163) to recover tax overpaid. The deadline is 31 December of the year following the tax year.

The question comes round every autumn: do I have to file a tax return in Luxembourg, or not? For an employee whose tax is already withheld on the payslip, the answer is not obvious, and many file a return without being required to, or let a refund they were owed slip away. Here, without jargon, is who must file a personal return, who can skip it, which form to use and by when.

Who has to file a tax return in Luxembourg?

A Luxembourg resident is required to file an income tax return, known as assessment (imposition par voie d'assiette), in three main cases: when taxable income exceeds 100,000 €, when several salaries or pensions subject to withholding are drawn at the same time, or when more than 600 € a year of income not withheld at source is received. Outside those situations, filing is usually not mandatory.

The starting principle is simple: in Luxembourg, salary and pension are taxed at source, month after month, through the tax card. For someone whose only income is that, the tax is in theory already settled, and the administration asks for no return. The filing obligation appears when that monthly withholding no longer captures the full tax actually due: high income, several sources, or income that escapes withholding.

The three thresholds, in plain terms

The Direct Tax Administration sets precise thresholds. Here they are, for a resident, in the most common cases.

The third case catches the most people. As soon as you take in more than 600 € of income not withheld at source, filing becomes mandatory, with no further floor. This covers, among others, commercial or professional profit, rents, annuities, miscellaneous net income or foreign-source income. A Luxembourg employee who rents out a flat, earns side fees or receives income abroad therefore moves into the obligation, even if their salary stays modest.

The second case concerns households with several tax cards, for example a couple where both partners work, or a person who combines a job and a pension. Withholding applied separately to each source does not account for their sum, and the progressive scale catches up the difference at filing time. That is why the threshold there is lower.

A company director is almost always concerned

If you run your own company, the question rarely arises: you file. A manager who pays themselves a salary and dividends by definition combines several kinds of income, and the dividend, even after its 15 % withholding, has to be reported in the return for final taxation on half of its amount. We set out this trade-off between salary and dividends in our article on paying yourself as a SARL manager.

Take care not to confuse two separate returns. The return this article is about is the one for the individual, the director or the employee. It has nothing to do with the return for the company itself, form 500, which covers corporate income tax, municipal business tax and net wealth tax. These are two separate obligations, and we cover the company's one in our guide on the corporate tax return in Luxembourg.

Form 100 or annual adjustment: two paths not to confuse

When your situation requires you to file, you complete form 100, the personal income tax return. The administration then recalculates the tax on all your income, compares it with what has already been withheld or paid in advance, and issues a tax assessment: you settle the balance, or you are refunded. Form 100 is filed online on MyGuichet.lu with LuxTrust authentication.

When filing is not mandatory, a second path exists, often overlooked: the annual adjustment, form 163. It is a lighter regularisation, reserved for employees and pensioners whose income has already been withheld at source. It allows you to recover an overpayment, for instance when your work-related expenses, special expenses or a change of salary during the year led to more tax being withheld than necessary. The annual adjustment can never make you pay extra: at worst it changes nothing; at best it hands money back.

The practical rule fits in one line: if you are required to file, it is form 100; if you are not but think you have overpaid, it is the annual adjustment. Choosing the wrong one, or filing neither out of misplaced caution, often means leaving a refund on the table.

The deadline: 31 December, no longer 31 March

This is the change many have not taken in. The return and the annual adjustment must be filed by 31 December of the year following the tax year. For your 2025 income, the deadline therefore falls on 31 December 2026. The old 31 March cut-off no longer applies, from tax year 2022 onwards, according to the Direct Tax Administration's tax calendar.

This longer deadline is a convenience, not a reason to wait. The earlier you file, the sooner your assessment is issued, and the sooner any refund reaches your account. Aiming for the last week of December, by contrast, risks a missing document or an expired LuxTrust certificate at the worst moment.

Return and advances: two different things

One last point causes confusion. The return establishes your actual tax once the year is over. Advances, on the other hand, are quarterly instalments the administration asks for during the year from those with income not withheld at source, set from their last known tax. The two meet at the assessment: advances already paid are credited against the final tax. We explain this mechanism, and how to have an advance that has become too high or too low adjusted, in our article on income tax advances. To understand where the monthly withholding on your salary comes from, our guide on your Luxembourg payslip breaks down the move from gross to net.

The self-employed and the non-resident

Two situations follow their own logic. The self-employed file as a matter of principle, because their profit has never been withheld at source: they fall under assessment from the first euro of profit, and we devote a dedicated guide to them on the self-employed income tax return. The non-resident completes the 100 F version of the same form and in principle declares only Luxembourg-source income here, subject to the applicable tax treaty. They may, under conditions, ask to be treated as a resident in order to access certain deductions. These cross-border situations are read case by case, treaty in hand, and are not settled on a general rule.

The Advena difference: a return that is not prepared the night before

Most botched returns are botched because they are tackled too late, on figures that first have to be reconstructed. We take the problem the other way round. Because we keep our clients' books in the Odoo we configure for Luxembourg, a director's taxable income can be read continuously, not at the moment of filling in the form. When the deadline nears, the return is no longer a project: it is the tidying-up of figures that are already right, and you know what you will pay, or recover, early enough to plan for it. This coupling between the bookkeeping and the management system is at the heart of our approach, set out in our guide to accounting firms in Luxembourg, with its cost in our article on what an accounting firm costs.

Who our support brings nothing to

Let us be straight. If you are a resident employee with a single employer, no rental income and no foreign source, you probably have no mandatory return to file, and an annual adjustment fills itself out on MyGuichet.lu in an evening: paying for support for that makes no sense, and we will say so. At the other end, a complex wealth situation, with structures abroad or sharp optimisation stakes, calls for specialist tax advice that goes beyond fixed-fee bookkeeping. Our ground is the director and the Luxembourg SME of 1 to 50 employees who want tax that is kept, correct and anticipated.

Frequently asked questions

Do I have to file a tax return in Luxembourg?

A resident has to file a return (form 100) notably if taxable income exceeds 100,000 €, if several salaries or pensions subject to withholding are combined, or if more than 600 € a year of income not withheld at source is received, such as rents or foreign income. Outside those cases, an employee is usually not required to file.

What is the tax return deadline in Luxembourg?

The return and the annual adjustment must be filed by 31 December of the year following the tax year. Income for 2025 is therefore due by 31 December 2026. The old 31 March deadline no longer applies, from tax year 2022 onwards.

What is the difference between form 100 and the annual adjustment?

Form 100 is the full tax return, which can end in a balance to pay or a refund. The annual adjustment (form 163) is a lighter regularisation, reserved for employees and pensioners not required to file: it can never result in an extra charge, only return an overpayment.

Is it worth filing if I am not required to?

Often yes. By filing an annual adjustment, an employee can recover tax overpaid through work-related expenses, special expenses or a change of salary during the year. Because the adjustment can never lead to an extra charge, the step carries no financial risk.

Where do you file a tax return in Luxembourg?

Form 100 is filed online on MyGuichet.lu with LuxTrust authentication, which has largely replaced paper filing. The annual adjustment can also be done on MyGuichet.lu or on a form sent to the competent tax office.

Read next

• The self-employed income tax return in Luxembourg
• Paying yourself as a SARL manager: salary, dividends or both
• Income tax advances in Luxembourg: who pays them and how to adjust them
• The corporate tax return in Luxembourg: form 500, MyGuichet and deadlines
• Accounting firm in Luxembourg: the complete guide for an SME

Why Advena?

We keep the books of Luxembourg directors and SMEs inside the management system we deploy ourselves, on a fixed fee from 325 € per month, all in, with the tax return included. In practice, your taxable income can be read continuously, your return is prepared on figures that are already right, and you know your balance or refund before the deadline rather than after. The thresholds, forms and dates quoted here come from the Direct Tax Administration and Guichet.lu, consulted in October 2026; because amounts and scales are subject to revision, your tax assessment remains the reference for your situation. We inform and we point the way, without claiming a regulated title we do not hold.

Information current as at October 2026, based on the assessment conditions published by the Direct Tax Administration and the return and annual adjustment guidance from Guichet.lu. As thresholds and deadlines are subject to revision, check the official source before any decision. This article is for information and does not constitute tailored tax advice.