Form 500 corporate tax return in Luxembourg
The form 500 corporate tax return in Luxembourg brings three taxes together on a single form, filed by 31 December of the following year. Who files, calendar, MyGuichet filing, annexes and what a late return costs.
What is the form 500 corporate tax return in Luxembourg?
The form 500 corporate tax return in Luxembourg is the annual return through which a collective entity declares, on a single form, corporate income tax, municipal business tax and net wealth tax, and it is filed with the Administration des contributions directes no later than 31 December of the year following the tax year.
One form, three taxes: that is what sets form 500 apart, and it has an immediate consequence. The taxable result determined in the return feeds two separate assessments, corporate income tax and municipal business tax, while the wealth section establishes a base of its own, fixed at 1 January. A single mis-stated line therefore travels into several tax bills.
The return is prepared from the annual accounts: the form itself refers to the balance sheet and profit and loss account attached to it, and the tax adjustments — non-deductible expenses, depreciation, loss carry-forwards — are read against that starting point. The full route, from picking up the accounts to checking the assessment, is set out on our corporate tax return page.
This article deals with the form itself: who files it, by when, through which channel, what it contains and what happens if it is late. Rates are not repeated here: they are covered in our article on the corporate income tax rate, which also sets out the aggregate burden, municipal business tax included.
Which entities file form 500 in Luxembourg?
Form 500 is filed in Luxembourg by collective entities, starting with resident capital companies, to which are added the other bodies subject to corporate income tax. Tax-transparent entities fall under a different return altogether.
The first circle is that of the capital companies referred to in article 159, paragraph 1, A.-1 of the amended law of 4 December 1967 on income tax: public limited company, simplified joint-stock company, partnership limited by shares, private limited liability company, simplified private limited liability company and European company. For them, electronic filing is not a convenience but an obligation, since tax year 2017.
The other collective entities form the second circle. From tax year 2019, and again from tax year 2024, the tax administration extended the MyGuichet procedure to those entities, which may use it or file the model in PDF format. Those outside article 159, paragraph 1, A.-1 may use MyGuichet on a voluntary basis, or send the forms by post.
Two cases are worth separating out. Tax-transparent collective undertakings — civil companies, special limited partnerships not subject to municipal business tax, co-ownerships — do not file a form 500 but a return for the joint establishment of income, form 200 or 205. And a company in liquidation remains required to declare its income and its wealth every year, whatever the length of the liquidation operations.
| Entity | Return | Filing channel |
|---|---|---|
| Capital companies under article 159, paragraph 1, A.-1 LIR | Form 500 | MyGuichet mandatory since tax year 2017, with a LuxTrust product |
| Other entities subject to corporate income tax | Form 500 | MyGuichet on a voluntary basis, PDF model or post |
| Tax-transparent collective undertakings and co-ownerships | Form 200 or 205 | Return for the joint establishment of income |
| Company in liquidation | Form 500 | Annual duty to declare income and wealth maintained throughout the liquidation |
When to file form 500: from 7 April to 31 December
The form 500 return for a given tax year is filed in Luxembourg by 31 December of the following year: for tax year 2025, the forms have been online since Tuesday 7 April 2026 and the filing window runs until 31 December 2026.
The opening date changed recently, and the change passed many directors by. The tax administration announced on 17 January 2025 that forms would from then on be made available on the first Monday of April rather than the first Monday of February; the shift serves its pre-filling project, since employer data is only collected during the first months of the year. Tax year 2025 therefore opened on 7 April 2026.
The tax calendar calls for care on one point: the return filed during a given year carries the corporate income tax and municipal business tax of the preceding tax year, and the net wealth tax fixed at 1 January of the current year. Two periods coexist in the same form, which is why a balance sheet movement occurring at the end of a financial year shows up in two successive returns.
The deadline can be adjusted: any reasoned request to extend the filing deadline goes to the competent tax office, preferably by post or fax. Cash, however, does not follow the return but the quarterly advances, due on 10 February, 10 May, 10 August and 10 November for municipal business tax and net wealth tax, and on the March, June, September and December instalments for corporate income tax.
| Deadline | Purpose |
|---|---|
| First Monday of April | Forms for the preceding tax year made available, since 2025 |
| 7 April 2026 | Opening of the filing window for tax year 2025 |
| 31 December 2026 | Last day to file the tax year 2025 return |
| 10 February, 10 May, 10 August, 10 November | Quarterly advances of municipal business tax and net wealth tax |
| March, June, September, December | Quarterly advances of corporate income tax |
| On reasoned request | Extension of the filing deadline, addressed to the competent tax office |
How to file form 500: MyGuichet, LuxTrust and the professional space
Filing form 500 through MyGuichet.lu has been mandatory in Luxembourg since tax year 2017 for the capital companies referred to in article 159, paragraph 1, A.-1 LIR. A LuxTrust product, private or professional, is required both to access the procedure and to sign the return.
The procedure covering income tax, municipal business tax and net wealth tax of collective entities has featured in the catalogue of the MyGuichet.lu professional space since tax year 2015. Holding a professional space is the condition of entry; where the taxpayer is represented by a professional — a fiduciary, a licensed accountant, a lawyer — the tax administration recommends that filing go through that space rather than a private one.
The annexes and documents accompanying the return are transmitted in PDF format, attached to the procedure. That is a point of method that matters more than it looks: the quality of those documents governs how smoothly the file is processed, and a tax office that cannot find the detail behind a line item will ask for it, with the delay that implies.
For volume, the online assistant accepts being pre-filled from an XML file of seven megabytes at most, whose structure is published in the tax administration's integrator documentation. That is the channel accounting software publishers use to feed the return from the trial balance, manual entry then being confined to the properly tax-related headings.
What form 500 contains and which annexes go with it
The Luxembourg form 500 is built around successive blocks: general information on the entity, determination of taxable income and of the municipal business tax base, then taxable wealth. Complements and annexes are added according to the company's situation.
The most frequent annex in holding structures is form 506A, which carries the detail of income and operating expenses connected with the participations referred to in article 166 LIR. The detail of income exempt under article 115, number 15a, is declared on a free-form annex. The substantive consequences of those regimes are covered in our article on the recapture of deducted expenses.
Two complements come up regularly. Form SURC lists the exceeding borrowing costs incurred within the meaning of article 168bis LIR, in addition to the body of the return. Annex 999 is used, where municipal business tax is allocated between several municipalities, to declare the final allocation key when it diverges from the one initially applied.
The observation from our engagements is a constant one: it is not the boxes on the form that make a file run long, it is the annexes. Reconstituting the detail of a participation built up through successive contributions, or documenting the exceeding borrowing costs of intra-group financing, regularly takes longer than the return itself. Our pricing gives the order of magnitude for a return according to the complexity of the balance sheet.
| Annex or complement | Purpose |
|---|---|
| Form 506A | Detail of income and operating expenses connected with participations under article 166 LIR |
| Free-form annex | Detail of income exempt under article 115, number 15a LIR |
| Form SURC | Exceeding borrowing costs incurred within the meaning of article 168bis LIR |
| Annex 999 | Final key for allocating municipal business tax between municipalities, where it diverges from the initial key |
| Documents in PDF format | Annual accounts and supporting documents attached to the MyGuichet procedure |
Filing form 500 late: surcharge, assessment by estimate and correction
Filing form 500 late exposes a company in Luxembourg to a tax surcharge of up to 10% of the tax assessed, imposed by the tax office, and failure to file altogether leads to assessment by estimate of the taxable bases.
Late payment interest is added to that, at the full rate of 0.6% per month, due where the tax debt is not paid when it falls due. The detail that is often missed: where the return was not filed within the period allowed, that interest is computed not only on the tax assessed but also on the surcharge imposed for late filing. The cost of delay is therefore not capped by the surcharge.
Assessment by estimate is not a discretionary sanction but a duty of the tax office faced with a taxpayer who does not file: the tax debt is then fixed by estimate. A remedy exists — a claim to the director of the tax administration within three months of notification of the assessment, the director having six months to decide, silence opening the way to the Administrative Court — but it is argued on documents, and documents are precisely what was missing.
An error discovered after the event does not mean waiting for the assessment: the assistant allows a corrective return to be sent, with a mandatory five-hundred-character field stating which fields or annexes were changed against the initial return. We regularly see companies wait for an audit to correct a line that a corrective return would have settled in minutes.
Sources and verification
Written for Financial Services Luxembourg and reviewed before publication by Mickaël LOC, licensed accountant (authorisation 10077274). The deadlines, amounts, forms and procedures in this article were verified on 12 September 2026 against the official sources listed below.
The pages of the Administration des contributions directes supplied most of the material. The frequently asked questions on form 500 and the page on the return for collective entities in the electronic exchanges section, for filing no later than 31 December of the year following the tax year, for mandatory MyGuichet filing since tax year 2017 by the capital companies referred to in article 159, paragraph 1, A.-1 LIR, for the extension of the procedure to other entities in 2019 and again in 2024, for the LuxTrust product required both to transmit and to sign, for the procedure featuring in the professional space catalogue since tax year 2015, for annexes transmitted in PDF format, for pre-filling from an XML file limited to seven megabytes and for the corrective return with its mandatory five-hundred-character field. The collective entities forms page and the form 500 complements, for form 506A on participations under article 166 LIR, for the free-form annex on income exempt under article 115, number 15a, for form SURC on exceeding borrowing costs under article 168bis LIR and for annex 999 on allocating municipal business tax. The tax calendar, for the return carrying the previous year's income and the wealth held at 1 January of the current year, and for the quarterly advances. The page on filing and submission, for the reasoned extension request addressed to the tax office. The page on additional levies where filing and payment deadlines are not met, for the surcharge of up to 10% of the tax assessed, for late payment interest of 0.6% per month and for its computation on the surcharge itself. The page on appeal periods, for the three-month claim to the director and the six-month period to decide. The news item of 17 January 2025, for forms being made available on the first Monday of April, and the news items of 12 and 26 March 2026, for the opening on 7 April 2026 and filing until 31 December 2026. On guichet.lu, the pages on corporate income tax and on the tax calendar, for the filing duty of capital companies, for the professional space recommended where a professional represents the taxpayer, and for assessment by estimate.
Four limits must be flagged. The provisions of the general tax law underpinning the late filing surcharge and assessment by estimate were not read in their text: legilux.public.lu and the tax administration's PDF files are unreachable from our drafting environment, and those sources were consulted through indexed extracts. The page-by-page content of the tax year 2025 form could therefore not be checked line by line, and the exact title of the complement designated "CAR" in the administration's forms was not established: it is not cited here. Whether an extension of time carries a charge was not verified. Lastly, the March, June, September and December instalments of corporate income tax advances were verified by month, not by day. Readers can confirm these points on impotsdirects.public.lu and with their tax office.
This article states the law as it stands at the date of publication. Deadlines, amounts and procedures change, and any decision binding your structure must be checked on the date you rely on it. Report an error to contact@financialservices.lu: the correction is dated in the article.
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