Resident in Belgium, employer in Luxembourg

1The legal basis

The rule is based on the Belgium–Luxembourg double tax treaty of 17 September 1970 (article 15 and point 8 of the final protocol).

The amending protocol was approved in Luxembourg by the law of 22 June 2022 and published in Belgium in the Moniteur belge (official gazette) of 20 March 2023, with retroactive effect for 2022.

2What counts

According to Belgian circular AGFisc no. 22/2015, counting is strict:

• every working day outside Luxembourg, in Belgium or a third country, counts: telework, business trips, training;
• part of a day is enough to count as a full day, per 24-hour period, whether it is 15 minutes or 10 hours;
• checking your messages at home before leaving for the office does not count as a day in Belgium.

The following do not count: weekends, public holidays, holidays and force majeure. Sick days are not expressly covered.

3Part-time work and incomplete years

To be on the safe side, homeoffice.lu applies the reduction (34 × your working time, rounded down). If you work part time, ask the FPS Finance (SPF Finances) for confirmation before relying on the full threshold.

4If you exceed the threshold

As long as you stay below the threshold, your whole salary remains taxable in Luxembourg, including the days worked elsewhere. Beyond it, Belgium taxes every day worked outside Luxembourg, from the first one.

Belgium exempts the Luxembourg share subject to the progression proviso. On the municipal tax, the sources contradict each other: check your situation with the FPS Finance.

Tax withheld at source in Luxembourg on the Belgian share can be recovered through the Luxembourg tax return or the annual adjustment.

5Your tax return in Belgium

• Return filed on MyMinfin (Tax-on-web).
• Luxembourg salaries go in part IV, codes 1250 / 2250, and are declared as exempt foreign-source income.
• With foreign income, the online deadline is the longest (for 2025 income: 16 October 2026).

6Negotiations

According to the Luxembourg Minister of Finance (January 2026), no negotiations are under way with Belgium. The threshold remains 34 days. In March 2025 the Benelux Parliament recommended studying a 40 % threshold, with no binding effect.