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Not required to file a tax return? Here's why you should
Not required to file a tax return in Luxembourg? Filing could still put money back in your pocket. Find out why and simulate your refund for free on taxx.lu.
Good news: this year, you don't have to file a tax return.
Even better news: "don't have to" doesn't mean "nothing to gain".
Because while you were busy working, the taxman may have held back a little too much from your pay. If so, that money is yours. You just have to ask for it.
Here's when filing pays off, even when nobody's making you.
First up: why might you have overpaid?
In Luxembourg, your employer deducts tax at source every month. Handy. But that deduction rests on one simple assumption: that your situation stays exactly the same all year.
Real life is rarely that tidy.
Maybe you:
- started or left a job partway through the year
- had months with variable income, or none at all
- changed tax class (marriage, separation, a new baby)
- only worked in Luxembourg for part of the year
In each of these cases, your monthly deduction was worked out as if you'd earn that amount for twelve months. The result: you've often paid too much. An adjustment gets you the difference back.
An example
You land your first job in Luxembourg in September. Every month, tax is deducted at the rate that would apply if you earned that salary for a full year. But you only worked four months. So the rate was too high for what you actually earned. An adjustment recalculates on the months you really worked, and hands back the overpayment.
Two ways to get your money back
It all depends on your situation. There are two routes.
The annual adjustment (form 163)
The simple version. You ask the ACD, Luxembourg's tax administration, to recalculate your deductions over the year and refund the excess.
Its big selling point: in principle, an annual adjustment can't leave you with extra tax to pay. Either you get money back, or nothing changes. That's what it's built for.
On the flip side, it only lets you claim a limited number of deductions. If your gain comes mainly from too much tax withheld, it's the right tool for the job.
The voluntary tax return (form 100)
The full version. You file a proper tax return and claim all your deductions.
It takes a bit more work, but it opens the door to far more deductible items. Mortgage interest, for instance, can only be deducted this way. That's often where the real refund is hiding.
One or the other, per year
For any given tax year, you don't file both an annual adjustment and a tax return. The good news: you don't have to choose on your own. taxx.lu works out the right route for your situation.
What can tip the balance
These are the items that most often pay off, when they apply to you:
- mortgage interest
- insurance premiums and personal loan interest
- private pension savings (Article 111bis)
- home savings plans
- childcare costs
- extraordinary charges (illness, care, special circumstances)
- actual professional expenses, where they exceed the flat-rate allowance you already get
Some of these can only be deducted through a full tax return, not an annual adjustment. One more reason to check what applies to you before choosing your route.
See the result before you decide
On taxx.lu, you fill in your situation and your estimated refund updates in real time as you go. You'll know whether filing pays off before you finalise anything. Creating an account and running a simulation is free.
On average, our users get back €2,352. That's an observed average, not a promise: the ACD always sets the final amount. But it gives you a sense of what can be sitting unclaimed on the tax side.
How long do you have?
You've got time, but not forever.
For any given year's income, you can submit your request until 31 December of the following year. So for your 2025 income, you have until 31 December 2026.
Miss that deadline and the overpayment stays with the Treasury. Which would be a shame.
What if you're not sure you're really exempt?
Good question. "Not required" isn't the same as "never required". The obligation is assessed every year, and the ACD can also ask you to file.
We've covered every scenario here: Do you have to file a tax return every year in Luxembourg?
In short
- Not having to file doesn't mean having nothing to claim back.
- Too much tax withheld? An annual adjustment (form 163) sorts it, with, in principle, no risk of extra tax.
- Deductions to claim? A voluntary tax return (form 100) opens far more doors.
- You have until 31 December of the following year.
- The easiest move: run a free simulation and let the numbers decide for you.
