Can I be self-employed and work for someone else at the same time?

I am working as a self-employed, and I have been offered the possibility of working part-time as an employee in a real estate agency. My business is doing well, but an extra income would be great. Nevertheless, I do not want to have any problems, and with the current labour regulations it is not entirely clear to me if I can carry both jobs out, or if I must resign one of them.

Can I work as self-employed and as an employee in a company at the same time?

Yes, you can, there is no objection to this. On the one hand, you will have to continue paying the Social Security as a self-employed as you have been doing until now, and on the other hand, the real estate agency will have to make another payment to the Social Security for your employment.