Personal taxation · Luxembourg
Luxembourg tax return deadline for 2025 income
For 2025 income, the general deadline for submitting the tax return is 31 December 2026. The request for the 2025 annual tax adjustment (Form 163) is also due by 31 December 2026. Any specific deadlines set out in a letter from the Luxembourg Inland Revenue (ACD) must also be met.
Financial Services Luxembourg · Licensed accountant · Head of the firm: Mickaël LOC. Editorial update: .
Income year and filing year
The tax year refers to the income concerned; the filing campaign comes afterwards. Simply writing “2026 tax return” is ambiguous: it can mean a return sent in 2026 or the income of 2026.
For the campaign covering 2025 income, the ACD announced that the forms would be available from 7 April 2026. The general deadline does not cancel a specific deadline requested by a department of the administration.
| Procedure | Income concerned | General deadline |
|---|---|---|
| Form 100 | 2025 | 31 December 2026 |
| Annual tax adjustment on request | 2025 | 31 December 2026 |
| Reply to an ACD letter | As stated in the letter | Date set by the department |
| Challenging a tax assessment notice | Depends on the decision | Check the notification and the means of appeal; this is not the Form 100 deadline |
What to check before the last week
- Form for the correct year and up-to-date residence details.
- Supporting documents and schedules available, household income complete.
- Signatures and a mandate if a third party submits the return.
- Submission actually completed, not just saved as a draft.
- Acknowledgement of receipt or proof of dispatch kept.
Missing document, error or delay
Contact the competent tax office and document the point that is holding you up. Do not assume that a missing document, contact with a service provider or an electronic draft suspends the deadline.
Late filing can lead to administrative consequences. If a tax assessment notice or an estimated assessment already exists, the next step must be examined on the basis of that document. The general 31 December deadline is not a universal rule for corrections or objections.
Preparing an engagement in time
The administrative deadline is not the processing time promised by a firm. Feasibility depends on availability, on how complete the documents are and on the complexity of the file. A quote accepted late does not automatically mean a commitment to file.
The firm’s other tax engagements
Depending on your situation, the firm also handles tax, VAT and payroll, the regularisation of late tax filings and assistance during a tax audit. Fees are listed in the firm’s fee grid.
Official sources and scope
- Guichet.lu: electronic filing and deadlines
- ACD: 2025 income tax return campaign
- ACD: annual tax adjustment
The rules apply to the year and profile concerned. Examples flagged as fictitious explain a method; they are not an individual validation. The documents and options of your file are covered by a separate engagement.