Posted on
Pre-filled tax return in Luxembourg: don’t rely on it blindly
Your pre-filled tax return doesn't reflect your real situation. Missing deductions, outdated data: file your Luxembourg tax return with taxx.lu.
On 7 April 2026, the tax season officially opens for all Luxembourg taxpayers. The deadline to file your return in any form runs until 31 December 2026.
However, from 30 March 2026, certain eligible taxpayers will receive by post a pre-filled tax return from the Luxembourg Tax Administration (ACD).
On paper, the Administration's message is clear: speed things up, streamline the process. A ready-completed return to sign and send back in minutes. Less paperwork, less effort. The idea is appealing and that is precisely the problem. What many taxpayers fail to notice or underestimate is the mention included in the Tax Administration's own letter: This document has been generated
based on the data currently available to the Tax Administration (ACD). A technical detail with very real consequences.
Yet a tax situation is never set in stone. From one year to the next, your insurance premiums may have increased or decreased. You may have renegotiated your mortgage, amended your home savings contract, made a donation, or incurred significant medical expenses. Automatically rolling over last year's figures, or declaring no deductions at all, can therefore cost you far more than you might expect.
What the pre-filled return actually contains
The pre-filled return includes only your salary and/or pension income, as communicated to the Tax Administration by your employer or pension fund.
For everything else, two situations are possible depending on your profile:
- Either no deductions are entered at all: the return is blank of any deductible expenses,
- or the deductions mirror exactly those declared the previous year, with no updates whatsoever.
In both cases, the result is the same: your actual situation for the relevant tax year is not reflected. The Tax Administration does not hold your supporting documents, does not know how your contracts have evolved, and cannot adapt your return to what has changed in your life. If you sign and return this document without adding your own information, you risk paying significantly more tax than you should.
What the pre-filled return may not include:
Here are the main deduction categories that may be absent from the pre-filled return, but to which many Luxembourg taxpayers are entitled:
Deductible insurance premiums
Premiums paid for life insurance, supplementary health insurance, liability insurance, or mortgage protection insurance may, under certain conditions, be deducted from your taxable income.
Home savings
Contributions made to institutions such as BHW, Schwäbisch Hall, or Wüstenrot entitle you to a tax deduction in Luxembourg.
Old-age pension 111bis
Contributions made under an approved old-age provision contract.
Mortgage interest on your home loan
If you have taken out a loan to finance your primary residence, in Luxembourg or abroad, the interest you repay each month is deductible within the applicable legal limits. Loan set-up costs (notary fees, bank arrangement fees) may also be deducted in the year they are paid. These amounts can represent several hundred, or even thousands, of euros in deductions. **Without any action on your part, they are simply overlooked.
Charitable donations
Donations made to organisations approved in Luxembourg or abroad entitle you to a tax deduction above a certain annual threshold. Here too, the pre-filled return will not prompt you in any way.
Extraordinary expenses
Unreimbursed medical costs, childcare expenses (nursery, after-school care, domestic help), funeral costs, legal costs… These expenditures may qualify as deductible extraordinary expenses. Whether they are taken into account depends entirely on your own initiative.
The hidden risk: you face your tax assessment alone
Beyond missed deductions, the pre-filled return exposes you to another problem: without professional guidance, it is difficult to verify the accuracy of the data already entered by the Tax Administration, to assess whether the tax amount calculated is correct, and above all to spot an error once you receive your tax assessment.
If your assessment seems too high or the expected refund falls short of what you anticipated, you first need to notice it and know how to respond. Without personalised support, most taxpayers simply do not have the tools to do so.
Why the Tax Administration does not step in
The Tax Administration's role is not to optimise your tax position. Its function is to collect tax based on the information at its disposal. It does not have access to your insurance contracts, bank statements, or expense receipts. And it will not send you any reminder to invite you to claim deductions you are entitled to.
A complete return requires guidance
To avoid this, it may be worth turning to a dedicated solution. taxx.lu supports Luxembourg taxpayers at every step of their return, structuring the process so that no deduction falls through the cracks – including those that have changed compared to the previous year.
In practice:
- Each section is clearly explained, with eligibility conditions and the amounts to enter.
- At the end of the process, a personalised analysis identifies possible tax optimisations for the following year: insurance, savings products, old-age provision…
- The team is available by chat and email (help@taxx.lu) to answer any questions along the way.
- If you have doubts about your tax assessment, the Plus, Premium, and Platinum packages include a verification service and, where necessary, the drafting of a formal appeal letter to the relevant tax office.
Taking the time to complete your return correctly – or having someone guide you through it – remains the best way to pay only what you genuinely owe.
