The federal states decide whether the housing market in the respective city is considered tight or not. You can find an up-to-date overview of the cities in which the rental price brake applies here. The rental price brake is intended to prevent the rent from being raised sharply in the event of re-letting.
The landlord may therefore increase the rent by a maximum of ten percent above the local comparative rent. However, there are exceptions to this. This rule does not apply if the previous rent with the previous tenant was above this limit or if the apartment was modernized.
The rental price brake does not apply to new buildings either. This applies to apartments that were used or rented for the first time after October 1, 2014. The landlord must provide the tenants with information about all these circumstances.