As a student you receive each calendar year a set of 475 hours during which you can work by paying only a solidarity premium of the social security contribution.
You can check the number of hours left in your quota on the website of the Social Security Office Student at work and print an attestation with the number of hours that remains in your quota.
In order to log in you will probably have to apply for a federal token or in some cases you can log in with your Belgian residence permit or ID card.
For the calculation of the 475 hours only the effectively worked hours are counted and deducted from your quota (e.g. the hours of a paid bank holiday are not deducted from your quota, but you receive the wage with deduction of the solidarity premium).
In case you work more than 475 hours per calendar year as a student, the normal social security contribution (in general 13.07%) will be due as of the 476th hour. You can still keep your student status and you must be employed with a student employment contract.
Under certain conditions you can work additionally as a student in different industries on top of the 475 hours, e.g. as an occasional worker in the hotel and catering industry (in Dutch: ‘horeca’). Those days are also lower in cost for the employer.
You do not need to use the 475 hours of your quota first before you can work as an occasional worker or as an employee paying the regular social security contribution.
Conclusion: you can work more than 475 hours per calendar year with no or limited impact.
In some cases the employer can withhold an advance on the income tax from your wages called ‘bedrijfsvoorheffing’, however, most students are entitled to a refund of this tax.