The third quarterly advance payment for Luxembourg corporate income tax is due on 10 September, after which unpaid balances accumulate late-payment interest at 0.6% per month from the tax office. The schedule is fixed.
This is a recurring calendar deadline, not a new rule. Under the official schedule published by the Administration des contributions directes, the third quarterly advance for corporate income tax falls due on 10 September for the current tax year. The advance is an instalment towards the company's final corporate tax assessment rather than a separate tax. Missing the date leaves the balance open to statutory interest from the ACD.
Who pays, and who stays outside
The obligation applies strictly at corporate level. It binds incorporated commercial entities seated in Luxembourg or operating through a domestic establishment:
| Entity type | Subject to CIT advance on 10 September | Notes |
|---|---|---|
| Public limited company (SA) | Yes | Standard quarterly corporate tax schedule |
| Private limited liability company (SARL) | Yes | Standard quarterly corporate tax schedule |
| Simplified limited liability company (SARL-S) | Yes | Standard quarterly corporate tax schedule |
| Sole proprietorship | No | Taxed under personal income tax rules |
| Non-CIT legal entities | No | Excluded from corporate income tax advances |
Sole proprietors and unincorporated businesses do not fall under this schedule. Their income passes directly to personal income tax returns, which follow their own assessment tracks. For any incorporated structure subject to corporate income tax, the quarterly advance remains mandatory unless the ACD has formally revised or suspended the instalments for that tax year.
Four dates across the tax calendar
Luxembourg direct taxes do not run on a single combined timetable. The administration divides corporate income tax, municipal business tax, and net wealth tax across distinct quarterly cycles.
| Tax type | Advance payment dates | Setting body |
|---|---|---|
| Corporate income tax (CIT) | 10 March, 10 June, 10 September and 10 December | ACD assessment / fiscal calendar |
| Municipal business tax (MBT) | 10 February, 10 May, 10 August and 10 November | ACD assessment / fiscal calendar |
| Net wealth tax (NWT) | 10 February, 10 May, 10 August and 10 November | ACD assessment / fiscal calendar |
Corporate income tax instalments recur in March, June, September, and December. Municipal business tax and net wealth tax instalments share an alternate quarterly rhythm in February, May, August, and November.
The payment due on 10 September concerns only the corporate income tax tranche. A business that paid municipal business tax in August must still meet the September corporate tax instalment on time.
Where companies miss the timing
The most common breakdown around quarterly advances is simple oversight between accounting records and cash execution. Companies often track final tax assessments while treating quarterly advance notices as background administration.
The ACD fixes these advances automatically based on the latest tax assessment issued or the initial estimate established at incorporation. No fresh bill arrives. The tax administration does not reissue an advance notice before every single due date. Once the quarterly schedule is set in an assessment bulletin, the company must execute payments on those dates without waiting for a fresh demand.
When cash flow changes significantly, a company can submit a formal request to the competent tax office to adjust or reduce its advances. Until the tax office formally issues an amended calculation bulletin, the previously notified quarterly instalment remains legally payable. Simply underpaying the advance because trade dropped earlier in the quarter does not suspend interest.
If an official assessment bulletin arrives with an adjustment, the general rule is that direct tax liabilities must be settled within one month after receipt of the tax assessment. Where a business cannot meet a formal assessment bill, any application for a deferral must reach the tax inspector before the end of the month following receipt of the tax assessment. For routine quarterly advances, however, the scheduled date is fixed and the payment has to be initiated early enough to clear.
The sequence to follow before 10 September
Managing an advance means checking the current assessment bulletin and the bank's execution timing well ahead of the due date.
| Step | Action | Responsible party |
|---|---|---|
| Check current assessment | Confirm the exact CIT quarterly advance amount fixed by the ACD | Company management / accountant |
| Verify cash position | Allocate available funds to cover the third-quarter corporate tranche | Treasury / management |
| Execute transfer | Transmit bank instruction with correct tax identification references | Company bank signatory |
| Diarise next cycle | Record the fourth CIT advance for 10 December | Management |
10 September is the third milestone in the corporate income tax year, and the fourth and final CIT advance follows on 10 December. A company that has handed its accounting and tax filings to a retained accountant has both dates diarised by the person who also files the return.
The tax administration tracks statutory due dates, not internal company reminders. It allows no delay. Missing the September date produces interest, not flexibility.
Figures verified against impotsdirects.public.lu, guichet.public.lu, impotsdirects.public.lu, impotsdirects.public.lu on 2026-08-31.