Declaring a Luxembourg salary as exempt in your country of residence means asking for an exception — and whoever asks for the exception proves it. If the tax authority of your country of residence questions your count, it is not for them to establish that you were at home on a given Tuesday: it is for you to establish that you were in Luxembourg.
What has to be proved
Two things, day by day: that the day was worked, and that it was worked physically in Luxembourg. The employment contract and the payslips prove employment; they prove the location of no particular day. That is the whole difficulty: useful evidence is daily, and it cannot be manufactured after the fact.
The evidence that carries weight
The Belgian and Luxembourg authorities have agreed on the logic of proving physical presence. In practice, a solid file mixes two families of records.
Those that come from the employer:
- dated badge or clocking records;
- attendance sheets and approved schedules;
- assignment orders and approved expense claims;
- an employer's certificate summarising the days worked outside Luxembourg — useful, but rarely sufficient on its own: it asserts, it does not demonstrate.
Those that come from daily life:
- fuel or charging receipts, taken on the way or on site;
- till receipts, restaurant and parking tickets in Luxembourg;
- named travel tickets and passes;
- card payment records showing a location.
No single item is magic. What convinces is the body of evidence: a badge record corroborated by a parking ticket says more than ten certificates. And a record dated the same day will always be worth more than a document put together afterwards.
The days that need no proof
Holidays, public holidays, sick leave, weekends not worked: those days do not eat into the tolerance and call for no proof of presence — but they must stay consistent with the rest of the file. A day of leave booked with the employer that appears as a working day in the count, and the whole count loses its credibility.
Keeping the register rather than suffering it
The method that works is boring: note each day its status — in Luxembourg, working from home, travelling, on leave — and attach the day's record when there is one. Ten seconds a day, against weeks of reconstruction if the question arrives three years later, when the receipts have faded and the badge data has been purged. Audit periods are counted in years: a year's file is kept at least as long as the authority can reopen that year, and thermal paper is scanned before it fades.