All citizens living and working in Belgium are required to pay a minimum of taxes and most of them also pay social security contributions, the latter being the sums that partly finance the social security system. In general, the fiscal situation of each individual is evaluated in terms of the conventions for avoiding double taxation agreed with Belgium. It is therefore not possible to choose the place where you pay your taxes! Unless proved otherwise, the law assumes that individuals who are registered with a municipality (in the national register) have established their fiscal domicile in Belgium and must therefore declare all their income in Belgium, including both national and international income.
If you are a civil servant in an international institution, if you have a diplomatic status or are paid on a foreign payroll you will evidently not pay taxes or social security contributions to Belgium or you will pay them in your home country.
If you’re an employee on a Belgian payroll, your personal income tax, whether or not in the form of advances, will be directly deducted from your wages and you will receive only a net amount on your bank account. All other type of taxes are to be paid directly to the State, region or local administration.
Trying to avoid paying taxes or contributions will result in fines and interests that can pile up quite considerably if not followed up upon and can unexpectedly arrive after a few years. In any case always make sure to take the right action when receiving your annual tax form.
The main taxes for foreign residents in Brussels to be taken into account are Personal Income Tax and a Tax on a Second Residence.