That depends on how much you earn. If your income remains under a certain amount, then you do not have to pay tax. This maximum amount changes each year. The amount for 2018 is 11.042,86 euros. This is a gross amount, after deduction of social-security contributions.
Note, this amount only applies if you:
- have no other taxable income than the wages from your student contract;
- state no actual professional costs on your tax return (the tax authorities then calculate a fixed amount)
Are you in a different situation? Or do you still have a question? Then contact FPS (Federal Public Service) Finance.