The sponsor is self-employed

The sponsor is self-employed person en a natural person

The sponsor, who is self-employed and a natural person, must submit the following documents:

a copy of his most recent personal income tax assessment notice, or, if he has not yet received one, the copy of the last statement sent to the FPS Finance and the detailed simulation of this statement; and
proof that he is still engaged in a self-employed activity.

Since a long period of time may elapse between the sending of the most recent assessment notice by the FPS Finance and the submission of the application for family reunification, the sponsor is advised to also submit all the documents that may be relevant in the calculation of the tax, as well as all documents that make it possible to assess his current means of subsistence, for example:

Supporting accounting-related documents (balance sheets, bank accounts, invoice books, etc.);
proof of rental income earned;
A document showing the amount of social contributions paid, or proof that the sponsor is exempt from them.

This list of supporting documents is not exhaustive. If, in the opinion of the sponsor, the documents listed above do not enable the Immigration Office to properly assess his/her financial situation or needs, he/she should add any information or documents that would enable this assessment to be made.

It is also recommended that the sponsor provide any information or documents relating to his or her professional history as a self-employed or salaried worker, particularly if he or she is starting out as a self-employed worker, as well as any information or documents relating to a (significant) drop in income over a given period.

The amount taken into account in assessing means of subsistence is net income. Net income means the amount available to the individual after payment of taxes and social security contributions. If the amount of net income is less than the required legal amount (120% of the living wage), the sponsor must forward the documents described above and any documents that allow the Immigration Office to assess his own needs and those of his family.

The sponsor is business manager

A sponsor who is a business manager must submit the following documents:

a copy of his most recent personal income tax assessment notice, or, if he has not yet received one, the copy of the last statement sent to the FPS Finance and the detailed simulation of this statement;
A document showing the amount of social security contributions paid; and
a copy of his tax sheet 281.20, with proof that the document submitted to the Immigration Office is identical to the document sent to the FPS Finance (e.g., FPS Finance stamp, summary statement 325.20, with proof of mailing).

_{Please note: the sheet will not be considered if no withholding tax is mentioned, without legal justification, or if the withholding tax mentioned is not in accordance with the FPS Finance scales.

https://financien.belgium.be/nl/ondernemingen/personeel_en_loon/bedrijfsvoorheffing/berekening}

tax balances (which will only be taken into account if accompanied by supporting documents)
pay slips in the capacity of business manager;
personal bank account statements;
proof of rental income earned;