The corporate tax cycle in Luxembourg: returns, advances and assessments

A Luxembourg company does not file three tax returns. It files a single return (modèle 500) covering corporate income tax, municipal business tax and net wealth tax, and the deadline is 31 December of the year following the tax year. Filing is mandatory via MyGuichet.lu since tax year 2017 for resident capital companies, including the s.à r.l. and the s.à r.l.-S.

Payment runs on its own clock, ahead of the return: quarterly advances during the year, then a balance due one month after receipt of the tax assessment. File late and the tax office can add a supplement of up to 10% of the tax assessed; pay late and interest runs at 0.6% a month.

The filing, payment and recourse deadlines on this page were read in August 2026 on the Administration des contributions directes pages that publish them. The rates and thresholds — the combined rate, the reduced band, the municipal allowance and the minimum net wealth tax — were last checked against the ACD, guichet.public.lu and legilux in July 2026, for tax year 2025 onwards.

The ACD splits the filing calendar, the payment rules and the recourse deadlines across three separate pages, which is part of why founders assemble the cycle wrongly.

The cycle in three moves

Advances. The ACD fixes quarterly advances from your last known results. A new company usually starts at zero or close to it, because there is nothing to extrapolate from. Advances are adjustable in both directions on a reasoned request to the competent tax office — a collapse in trading justifies a reduction, a boom justifies asking for an increase rather than accumulating an unfunded balance.

The return. After year-end, one electronic return carries corporate income tax, municipal business tax and net wealth tax, built on the annual accounts the shareholders approved.

The assessment. The ACD processes the return and issues assessments (bulletins d'impôt) that reconcile the tax due against the advances paid. The result is a refund or a balance. Assessments frequently arrive long after the year they concern, and that lag is where the planning problem lives.

The three taxes below travel on one filing. They appear as separate rows because their advance dates differ, not because there are three returns to send.

Advance dates come from the ACD's calendrier fiscal. Net wealth tax reached that December deadline last of the three, which is why older guides still show it on a date of its own.

One return, three taxes — and the certificate that blocks it

The modèle 500 is a single file carrying three computations: the corporate income tax base, the municipal business tax base and the net wealth tax declaration, all built on the same approved annual accounts. There is no separate net wealth tax form to remember, and nothing is filed with your commune. What the electronic channel adds instead is a signing requirement — a LuxTrust product (private or pro) is required both to use MyGuichet and to sign the return.

That last requirement is the one that actually stalls files, because it is the only step in the cycle that depends on a person rather than a document. A return can be complete, reviewed and agreed, and still sit unfiled because the manager who has to sign it is abroad, has no LuxTrust product, or has one registered to a personal identity that no longer matches the mandate.

Order the certificate in the first weeks of the company's life, not in the week of the deadline — the identification step takes days, not minutes, and nobody can complete it on your behalf. The ACD's electronic filing page sets out the mechanics.

The second-year ambush

The sequence is arithmetic rather than bad luck: year one is profitable, but advances were minimal because the company had no history to extrapolate from. Year two then stacks three things — the balance for year one, the four year-two advances now recalculated upward on year-one results, and in some cases a retroactive catch-up on advances already passed. A company that spent its first year's profit meets that stack with nothing behind it.

The defence is unheroic: reserve as profits arise, not as bills arrive. A company seated in Luxembourg City faces a combined 23.87% on trading profits at the standard rate, so moving that share of each month's profit to a separate account converts the ambush into a transfer.

That over-provisions a company still inside the reduced band up to €175,000, and also one inside the transition band between €175,000 and €200,000, where corporate income tax is computed as €24,500 + 30% of the income above €175,000 rather than at the standard rate. The €17,500 municipal business tax allowance pulls the same way. That is the direction you want the error to run.

Note also that the cycle never falls to zero. Minimum net wealth tax applies in a loss year, set by the balance sheet: €535 up to €350,000, €1,605 up to €2,000,000, and €4,815 above that.

When you cannot pay the balance

The balance is due one month after receipt of the tax assessment. If the money is not there, the request for an instalment plan runs on its own clock — it has to reach the office before the end of the month following receipt of the tax assessment.

That is a different date from the payment deadline itself, and it is the one that decides which column of the table below you land in: an arrangement asked for in time, or a debt in recovery. The price difference is not a rounding error.

Those bands are published on the ACD's délais de paiement page rather than settled case by case: the length of the plan sets the rate, and the rate does not move because the conversation went well.

What is open to discussion is the schedule inside a band — how many instalments, on which dates. An arranged plan carries a small fraction of the monthly interest charged on tax simply left unpaid, which is the whole argument for making the call early rather than hoping the balance goes unnoticed.

If the assessment looks wrong

Assessments are not self-verifying: they are your return plus whatever the office adjusted, and adjustments are not always explained in a way a founder recognises. Check each one against the return that generated it, line by line, in the week it arrives.

The clock is unforgiving on one point in particular: notification is presumed to take place on the 3rd working day after the assessment is handed to the post, not the day you opened the envelope or logged into MyGuichet. Time spent waiting for your accountant to come back from holiday is time spent inside the deadline.

If the director does not answer the réclamation within 6 months, the taxpayer may go straight to the Tribunal administratif rather than wait indefinitely. The deadlines are set out by the ACD under voies de recours and in plainer language on guichet.public.lu.

Losses, and why filing on time protects them

Startup losses are not wasted: losses offset future profits for the 17 most recent closed financial years, oldest first; no carryback. In practice that value only exists if the losses were declared in returns that were actually filed, on the accounts that were actually approved. A year skipped because "there was no profit anyway" is the most expensive kind of silence in the whole cycle — it removes a deduction from a profitable year that has not happened yet.

Common questions

The cycle turns on a small number of dates: when the return is due, whether that date can move, how advances are reset, and the two clocks that start the moment an assessment lands. The short answers are below; the mechanics behind each of them are in the sections above.

When is the corporate tax return due in Luxembourg?

31 December of the year following the tax year, on a single return covering corporate income tax, municipal business tax and net wealth tax.

Can I get an extension?

An extension is available only on a reasoned request addressed to the competent tax office, preferably by fax or post. The ACD publishes no fixed extension period, so treat any extra time as discretionary rather than routine — and remember the late-filing supplement can reach 10% of the tax assessed.

How do I get my advances changed?

By a reasoned written request to the tax office holding the file, with the figures behind it — interim accounts, an order book that emptied, a contract that ended. Advances follow the last assessment until someone shows the office why they should not.

How long do I have to contest an assessment?

3 months from the day the tax assessment (bulletin d'impôt) is notified, addressed to the director of the Administration des contributions directes. The clock runs from presumed notification, not from receipt.

What does a late payment cost?

0.6% a month on tax unpaid at its due date, against no interest at all on an agreed plan of up to 4 months, 0.1% a month on a plan of 5 to 12 months, and 0.2% on one of 13 months to 3 years.

What to do in year one

Each of these is a calendar entry or a single order, and every one of them is cheaper to do now than in the week of a deadline.

1. Order the LuxTrust product for whoever will sign the return, in that person's own name, in the first month.
2. Diarise the advance dates in the table above, even if your advances are currently set at zero.
3. Reserve monthly at the combined standard-rate figure rather than provisioning once a year.
4. Read every assessment against the return within days of arrival, because the objection window runs from presumed notification.
5. If cash is short, request the plan so it reaches the office before the end of the month following receipt of the tax assessment, not after the reminder.
6. Line the tax cycle up with the accounts cycle. That leg runs on company law and the register rather than the tax calendar: the shareholders approve the accounts within 6 months of year-end, the filing follows within 1 month of that approval — 7 months from year-end at the outside — and the return is built from those approved accounts. One compliance calendar keeps all of it in view.

The cycle rewards nothing clever. It rewards a certificate ordered early, a reserve nobody touches, and an assessment read the week it lands.