Luxembourg income tax return: who files, when and how

Direct answer

An individual files an income tax return (form 100) when they fall within one of the assessment cases set by article 116 of the amended law of 4 December 1967 on income tax (LIR) and its implementing grand-ducal regulation. The deadline is 31 December of the year following the tax year, a rule applicable since tax year 2022. Filing is done on MyGuichet.lu or on paper with the competent tax office.

Anyone outside those cases is not required to file. They may still request an annual adjustment (form 163) or file a voluntary return to claim expenses, insurance premiums or loan interest that the monthly withholding on salary did not take into account.

Who has to file

The most frequent cases of obligation for a resident, as published by the Luxembourg Inland Revenue (ACD) on guichet.lu, fit in a short list. Each line is a threshold, not a judgement call.

Annual taxable income exceeds the threshold of EUR 100,000. The taxpayer combines several remunerations subject to withholding (salaries, pensions, including those of a jointly taxed spouse) and their total exceeds the threshold of EUR 36,000 in class 1 or 2, or EUR 30,000 in class 1a. They receive income not subject to withholding at source (rent, commercial or agricultural profit, self-employed income, foreign income) above EUR 600 a year. They receive Luxembourg capital income subject to withholding above EUR 1,500. They opted for joint taxation with a non-resident spouse, or the ACD sent them a form.

A single employee with no other income, below the EUR 100,000 threshold, is therefore not required to file. That is the most common situation, and also the one where the annual adjustment pays off most.

The calendar

The calendar is the same for all residents and for non-residents filing in Luxembourg. The only date that matters is the filing date; advance payments, where they exist, are set by the ACD on the basis of the last known assessment.

MyGuichet or paper

Electronic filing through MyGuichet.lu (guided assistant, LuxTrust, GouvID or eIDAS authentication) is the route recommended by the ACD: built-in consistency checks, time-stamped acknowledgement, PDF attachments. The paper form remains accepted; it is filed with or sent to the tax office of the taxpayer's residence, and the date of receipt is what counts.

Documents to keep, without attaching them systematically: salary and pension certificates (issued by the employer or the pension fund), interest certificates, insurance and pension-scheme certificates, evidence of deductible expenses, rental statements. The ACD may request them during the review period.

Tax classes and joint taxation

The tax class (article 119 LIR) determines the rate schedule. Class 2: spouses or partners taxed jointly, and some transitional situations after widowhood or divorce. Class 1a: single persons with a dependent child, widowed persons, taxpayers aged 64 on 1 January. Class 1: all other single persons.

Resident spouses are taxed jointly by default (article 3 LIR), with the option of individual taxation. Married non-resident cross-border workers only obtain class 2 by requesting assimilation to residents under article 157ter LIR: at least 90 % of the taxpayer's worldwide income taxable in Luxembourg, or non-Luxembourg income below EUR 13,000, or, for a Belgian resident, more than 50 % of the household's professional income from Luxembourg sources. Assimilation is obtained through the return, not through the withholding card.

Remote work changes the taxable base of cross-border workers beyond the treaty thresholds: the count is detailed in our article on the two cross-border remote work thresholds.

Late filing, no filing, corrections

A return filed after 31 December exposes the taxpayer to a late-filing supplement capped at 10 % of the tax assessed (§ 168 AO) and to a penalty payment for as long as the return is missing (§ 202 AO). No return at all leads to an estimated assessment (§ 217 AO): the office sets the tax on the elements it holds, and the taxpayer has to challenge it within the deadlines of the assessment notice.

An error found after filing is corrected by an amended return as long as the assessment has not been issued, then by a written claim to the director of the ACD within three months of notification (§ 228 AO). The tax balance is due one month after notification; beyond that, late-payment interest runs at 0.6 % per month (§ 155 AO).

Self-employed and directors: what changes

A self-employed person, a manager paid through director's fees or a shareholder receiving dividends is almost always under a filing obligation: their income is not, or not fully, subject to withholding. Their return relies on the accounting result of the activity, which must be closed before filing; the calendar of self-employed accounting and that of the return therefore have to be run together.

On the company side, the counterpart of this return is form 500, described in the form 500 corporate tax return; the two never substitute for each other. For the preparation and filing of the personal return, see our page on personal income tax returns.