Working in Luxembourg, living in Belgium: how your salary is taxed
Luxembourg taxes your salary through the wage tax your employer deducts. Non-residents are in tax class 1 by default, even when married; class 1a applies to single parents, widowed people and people aged 64 or over. A married couple can ask for assimilation when at least 90 % of the worker’s income is taxable in Luxembourg or, for Belgian residents, when more than half of the household’s professional income is taxable there; the calculator uses the collective rate (class 2) only if it is cheaper. Luxembourg social security applies to the whole salary; health cover is through the CNS.
Up to 34 days a year worked in Belgium or in a third country are tolerated; for Belgium the threshold is not reduced for part-time work. Above 34 days, Belgium taxes the pay for all those days from the first day and Luxembourg taxes only the rest.
Belgium exempts the Luxembourg salary with progression: it taxes only the pay for days above the threshold, at the rate that applies to your total income. The calculator approximates this Belgian tax with the Belgian withholding formula, including an average municipal surcharge of 7 %. Not included: the effect of your Luxembourg salary on your spouse’s Belgian tax.