Income tax return for the self-employed in Luxembourg

In short. A self-employed person in Luxembourg reports their profit on the personal income tax return, form 100 (modèle 100), to be filed no later than 31 December of the year following the income year (2025 income is therefore due by 31 December 2026). The profit is added to your other income and taxed on the progressive scale. The return is completed online on MyGuichet.lu. Well prepared, it takes an evening; badly prepared, it costs surcharges and VAT reclaimed too late.

The tax return is the appointment self-employed people put off the most, and the one that costs the most when it goes wrong. Unlike an employee, whose tax is withheld at source every month, a self-employed person reports their own profit once a year and settles up afterwards. Here is how that return actually works in Luxembourg, which form to file, by when, what is deductible, and the specific case of the cross-border worker.

Who has to file a tax return as a self-employed person?

As soon as you carry on a self-employed activity that produces a profit, you fall under assessment-based taxation: you are required to file a return, whether your activity is commercial, craft or professional, and whether you are a resident or a non-resident. This is a fundamental difference from an employee, who is often exempt from filing while staying under certain thresholds. The self-employed person, by contrast, files as a matter of principle, because their income has never been subject to a monthly withholding.

The scope of your accounting and social obligations, ahead of the return, is set out in our guide to an accountant for the self-employed and freelancers in Luxembourg. This article focuses on the tax step: the return itself.

Form 100, MyGuichet and the 31 December deadline

The personal income tax return has a code name: form 100 (modèle 100). The same form serves resident and non-resident taxpayers; its 100 F and 100 D versions are simply the French and German editions, not two different regimes. Since tax year 2021, it is completed and signed online on MyGuichet.lu with LuxTrust authentication, which has largely replaced the paper filing.

The deadline has changed, and many still do not know it. The return must be filed no later than 31 December of the year following the income year, according to the fiscal calendar of the Direct Tax Administration (Administration des contributions directes). For your 2025 income, the deadline is therefore 31 December 2026. The old 31 March date no longer applies. This longer window is a comfort, not an invitation to wait: the earlier you file, the sooner your tax assessment is issued and your position settled.

How your profit reaches the return

The heart of a self-employed person's return is reporting their profit. Depending on your activity, that profit falls into two distinct income categories. A trader, craftsperson or manufacturer reports a commercial profit (bénéfice commercial). A member of a liberal profession (a consultant, a legal or medical professional, an independent intellectual occupation) reports a profit from a self-employed profession. The distinction is not cosmetic: it drives certain rules for working out the result and your accounting obligations.

This profit is not taxed in isolation. It is added to your household's other income (a spouse's salary, rental income, pensions) to form the overall taxable income, taxed on the progressive scale. In 2026, that scale rises to a top marginal rate of 42%, plus the employment-fund surcharge of 7% (9% above a certain income). In other words, each additional euro of profit is not taxed at the same rate as the first: that is the logic of progressivity, and it is what makes anticipation worthwhile. Working out the profit correctly requires books kept under the PCN 2020 chart of accounts, the foundation we set out in our guide to accounting firms in Luxembourg.

What you can deduct, and often forget

A profit is reported net of the costs that produced it. Beyond the day-to-day business expenses already booked, the return opens three levers that self-employed people underuse.

• Your social contributions. The contributions paid to the Joint Social Security Centre are deductible. As they weigh in at around 24% of income, the stake is far from marginal; we detail the mechanism in our article on self-employed social contributions in 2026.
• Special expenses. Loan interest, insurance premiums, pension savings, donations: these items are reported outside the profit, in a dedicated section, and reduce the overall taxable income.
• Deductible costs and allowances. Depending on your situation, several allowances (for extraordinary charges, for example) further reduce the taxable base.

Each of these levers has its conditions and ceilings, revised regularly. We inform here that they exist; their exact application is worked out on your own file, not on a general rule.

Resident, non-resident, cross-border: which return?

Your place of residence does not change the form, but it changes the scope of what Luxembourg taxes. A resident self-employed person reports all their income, including foreign income, in Luxembourg. A non-resident self-employed person, working in the Grand Duchy while living in France, Belgium or Germany, in principle reports only their Luxembourg-source income there, subject to the tax treaties between the countries.

The cross-border self-employed worker deserves particular care: their tax straddles two states, and the same rule can read differently depending on the applicable treaty. They can also, under conditions, ask to be treated as a resident to benefit from certain deductions. This is exactly the kind of situation where a general answer misleads: we set out the Luxembourg framework here and point you towards a dedicated review for your personal case.

The return is not the advance: don't confuse the two

Many self-employed people mix up two things that have nothing to do with each other. There is the annual return, which establishes your real tax once the year is over. And there are the quarterly tax advances, which the Direct Tax Administration sets in advance, based on your latest known profit, and which you pay during the year. The two meet at the tax assessment: if your advances came to less than the tax actually due, you pay the difference; otherwise you are refunded.

The trap is identical to the one with social contributions: a fast-growing activity pays advances pegged to a lower past income, and discovers a hefty tax balance on the assessment. The remedy is the same: estimate your profit as accurately as possible and, if needed, ask for the advances to be adjusted. That means knowing your expected profit during the year, which real-time accounting allows and books closed the following spring rule out.

Do you need an accountant for your return, and what does it cost?

Nothing requires a self-employed person to use a professional for their return. A simple file, in a liberal profession, with few expenses, can be completed alone on MyGuichet.lu. Delegating pays off when the return stops being a formality: commercial profit with stock or fixed assets, a cross-border situation, several income sources, or simply a year where a mistake would cost more than support.

The market most often bills by the hour, between 70 € and 300 € excluding VAT, without publishing a price, which we break down in our article on what an accounting firm costs in Luxembourg. At Advena, the tax return is not a separate line: it is included in the support fee from 325 € per month, all in, like the VAT returns and the annual accounts. You do not get a surprise bill in December because your form 100 had to be filed.

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

Most botched returns are botched because they are prepared too late, from books that are themselves behind. We take the problem from the other end. Because we keep your books inside the Odoo we configure for Luxembourg, your profit is readable continuously, not at the moment of filling in the form. When the deadline comes, the return is not a project: it is the fair copy of figures that are already accurate. And because we see your expected profit during the year, we adjust your advances and your contributions before they turn into a back-payment. It is the coupling between bookkeeping and the management tool, described in our guide to accounting firms, applied to tax.

Who this support brings nothing to

Let's be plain. If you are in a liberal profession, with a handful of invoices a year, no stock and no cross-border situation, your return fits on MyGuichet.lu in an evening and paying a monthly fee for that makes no sense: we will say so. Conversely, a complex, multi-company or heavily international structure belongs with specialist tax advice that goes beyond fixed-fee bookkeeping. Our ground is the self-employed person and the Luxembourg SME of 1 to 50 employees who wants a return that is accurate, on time, and backed by up-to-date figures.

Frequently asked questions

What is the tax return deadline for a self-employed person in Luxembourg?

The personal income tax return, form 100, must be filed no later than 31 December of the year following the income year, according to the Direct Tax Administration's calendar. Income for 2025 is therefore due by 31 December 2026. The old 31 March deadline no longer applies.

Which form does a self-employed person use?

Form 100, the personal income tax return, valid for both residents and non-residents. The 100 F and 100 D versions are simply the French and German editions. Since tax year 2021, it is filed online on MyGuichet.lu with LuxTrust.

How is a self-employed person's profit taxed?

The profit, commercial or from a liberal profession, is added to the household's other income and taxed on the progressive income tax scale, whose top marginal rate reaches 42% in 2026, plus the employment-fund surcharge of 7% (9% for high incomes).

Does a cross-border self-employed worker have to file a Luxembourg return?

Yes, as soon as they earn a Luxembourg-source profit. They in principle report only their Luxembourg income, subject to the applicable tax treaty, and can under conditions ask to be treated as a resident. Their personal cross-border situation is looked at case by case.

Are social contributions deductible from tax?

Yes. The contributions paid to the Joint Social Security Centre are deductible from taxable income. As they represent around 24% of professional income, accounting for them correctly weighs noticeably on the final tax.

Read more

• An accountant for the self-employed and freelancers in Luxembourg
• Self-employed social contributions in Luxembourg in 2026
• What an accounting firm costs in Luxembourg: fixed fee, hourly rates and hidden extras
• Corporate tax in Luxembourg: CIT, MBT and net wealth tax
• Accounting firm in Luxembourg: the complete guide for an SME

Why Advena?

We keep the books of self-employed people and SMEs in Luxembourg inside the management tool we deploy ourselves, on a fixed fee from 325 € per month, all in, tax return included. In practice, your profit is readable continuously, your return is prepared on figures that are already accurate, and your advances and contributions are adjusted before the back-payment. The deadlines and the workings of form 100 quoted here come from the Direct Tax Administration and Guichet.lu, consulted in August 2026; as scales and ceilings are revisable, your tax assessment remains the reference for your file. This article is for information and does not constitute individual tax advice.