Prospective tenants of furnished apartments in Berlin prefer to remain flexible with the rental period. Most of the time they are not sure if they want to extend the lease or not. While discussing this option with your tenant, just remember that they are only required to let you know if they'd like to extend, one month before they move out.
This is important to us too because we need adequate time to find the next tenant for you. A good tenant is one who has taken proper time to plan his stay in Berlin and not someone who registers today for an apartment tomorrow. With more time, the possibility of finding a tenant who wants to stay for longer is higher.
It is important that you properly discuss the option to extend the lease with the tenant, especially the dates by which the tenant needs to inform you of their decision to extend.