Personal taxation · Luxembourg
Annual tax adjustment Luxembourg: Form 163 or Form 100?
The annual tax adjustment (Form 163) regularises the tax withheld on salaries and pensions for taxpayers who are not admitted to an assessment based on a tax return. Form 100 is used for that assessment. The choice depends on your tax situation and the claims you make, not only on how simple the form is.
Financial Services Luxembourg · Licensed accountant · Head of the firm: Mickaël LOC. Editorial update: .
Two procedures with a different scope
Start by checking whether you are required or admitted to file Form 100. The annual tax adjustment must not be used to get around a required tax return. Conversely, an employee with no filing obligation should not be steered automatically towards a full tax return without checking which procedure fits.
| Question | Form 100 | Form 163 |
|---|---|---|
| Purpose | Annual assessment based on a tax return | Regularisation of tax withheld on salaries and pensions |
| Residence | Rules for residents or non-residents to apply | Versions 163 R and 163 NR |
| Assimilation of non-residents | Request examined through the tax return | Does not replace the request for assimilation to resident taxpayers |
| Documents | Depending on the income categories and annexes | Certificates, periods and allowable expenses, depending on the case |
Residents and non-residents: do not transpose the sections
Form 163 R and Form 163 NR do not have the same scope. For a resident, special expenses and other charges may be examined in the adjustment, subject to the conditions. Interest on an owner-occupied home leads you to consider Form 100 rather than simply adding it to Form 163.
For a non-resident, the periods worked in Luxembourg, foreign remuneration and the rate rules may come into play. A file that starts during the year therefore requires more than the certificate from the Luxembourg employer alone.
Can joint taxation apply in the annual adjustment?
Yes, in particular for resident spouses taxed jointly, where the conditions are met. Stating that only a Form 100 tax return allows any form of joint taxation would be inaccurate. You need to distinguish the joint annual adjustment from certain options that are exercised through a tax return.
The right question is which regime the household is admitted to and which expenses or options it wishes to claim.
Refund and documents
A refund requires the tax withheld to exceed the tax resulting from the adjustment. The procedure on request does not, in principle, lead to the collection of additional tax, subject to the specific cases provided for. This does not relieve you of checking that the annual adjustment is the right procedure.
- Annual Luxembourg and foreign certificates, depending on the file.
- Periods of employment, pension and inactivity.
- Certificates for the expenses you are asking to have taken into account.
- Contact details and supporting documents required by the form for the year.
When to file?
The annual tax adjustment requested for year N must be submitted no later than 31 December of year N+1. For 2025 income, this means 31 December 2026. The competent RTS office and the tax office handling Form 100 must not be confused.
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
- ACD: annual tax adjustment
- Guichet.lu: annual tax adjustment for residents
- Guichet.lu: annual tax adjustment for non-residents
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.