Personal taxation · Luxembourg
Form 100 Luxembourg: prepare and file your tax return
Form 100 is the income tax return for individuals taxed by assessment in Luxembourg. It is used to declare the categories of income and the items needed for the annual calculation. You must choose the form for the tax year, check the schedules and keep proof of filing.
Financial Services Luxembourg · Licensed accountant · Head of the firm: Mickaël LOC. Editorial update: .
Start with the year and the reason for filing
A return filed in 2026 may relate to 2025 income. The supporting documents, rules and forms must all match that year. Whether you are required to file and whether a voluntary request is worthwhile are two different questions.
Read any letter from the Luxembourg Inland Revenue (ACD) before choosing a procedure. The conditions vary according to residence, income and the options exercised. The annual tax adjustment (Form 163) is not a substitute for Form 100 when assessment by tax return applies.
Prepare the sections in a verifiable order
- Identify the taxpayers, their residence and the family situation for the year.
- List income by person, category and country before entering it.
- Reconcile salaries, pensions and withholdings with the annual certificates.
- Prepare the schedules needed for rental income, business activities or other income.
- Review expenses, outgoings and deductions on the basis of the certificates.
- Check options, signatures and documents; reread the summary before submitting.
Fictitious example: salary and a rented flat
A resident employee owns a rented flat. The salary certificate and the rents do not go into a single section: each type of income must be dealt with in its own category. The rental statement must separate receipts, allowable expenses, interest and any depreciation.
The total of credits to the bank account is not taxable income. A transfer between personal accounts is not rent, and capital repaid to the bank is not interest.
MyGuichet, PDF or paper
The electronic assistant is one filing channel, and its access conditions must be checked for the campaign concerned. The other officially offered channels remain to be considered if the file falls outside the scope of the assistant.
A representative must hold the required mandate; Form 101 is intended for the electronic procedure under the published conditions. A return saved as a draft is not a submitted return. Keep the version sent, the schedules and the acknowledgement of receipt.
Deadline for 2025 income
The general filing date is 31 December 2026 for tax year 2025. Letters from the ACD may set specific deadlines that must be met. A missing document or a technical difficulty should be taken up with the competent tax office, rather than waiting silently for the deadline to pass.
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: forms for individuals
- Guichet.lu: electronic filing and deadlines
- ACD: assessment based on a tax return
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.