Students in Germany are allowed to work along their studies, but in order to keep your student insurance there are a few rules to follow.
As a general rule: As long as studies are your main occupation, and paid employment remains secondary to your studies, you can keep your student insurance and will remain exempt from paying full social contributions. In these situations you remain in charge of your health insurance contributions - the employer does not pay for it.
This applies to the following types of employment:
Mini-job: You may earn up to €538 - no matter how many hours you work.
Short-term employment: The job is limited from the beginning to a maximum of 3 months (70 working days).
Working student contract: It doesn't matter how much you earn as long as you work a maximum of 20 hours per week. In addition, you are allowed to exceed 20 hrs per week during semester breaks for a maximum of 26 weeks per year in total.
Paid internships: are also mainly free of social contributions as long as they are happening during studies. You can read more about this topic in our internship article.
If however, none of the above-mentioned scenarios address your situation, and you are working over 20 hrs on a regular employment contract, you have to be insured through the employer, and not as a student.
If you are an international student on a residence permit, keep in mind that these rules generally correspond with Visa work restrictions - students on a residence permit are allowed to work part-time (20 hours per week) during the semester and full-time (40 hours per week) during breaks. This means that during a year, you can work a maximum of 120 full days or 240 half days without requesting approval from the German Employment Agency.
If you are from EU/EEA or any country Germany has a social agreement with, which allowed you to stay on your home insurance during your studies, you will have to pass to German insurance as soon as you take any of the mentioned types of employment. If you are under 30 years of age, you can sign up for student public insurance, and if you are over 30 you can sign up for Expat insurance.
Exemption: Denmark, Luxembourg, and Austria signed additional agreements with Germany, so if you are insured in one of these 3 countries you can stay on your home insurance even if you take any of the above-mentioned types of employment.