Until December 31, 2021, the Belgian authorities do not take into account the days worked from home due to Coronavirus for the determination of the applicable social security legislation.

As a general rule, an employee must pay social security in the country of employment on the basis of European rules. However, when an employee works at least 25% in his or her country of residence, s/he has to pay social security there, and no longer in the country where s/he works. If an employee has to work more at home, this may lead to a change in the applicable social security regime.

In order to avoid this, the Belgian authorities decided at the beginning of the coronavirus crisis not to take into account temporary working from home. As the coronavirus crisis persists, they have now decided to extend this tolerance until 31 December 2021.

Source

SDWORX