In many (but not all) cities and municipalities in Germany, you as a tenant or landlord can refer to a qualified rent index in order to assess the amount of a residential rent or the permissibility of an increase.

A qualified rent index has been drawn up in accordance with recognized scientific principles and has been approved by the local authority or by representatives of landlords' and tenants' interests.

The qualified rent index should be adjusted to market developments every two years. This can be based on a random sample or the development of the price index for the standard of living for all private households in Germany as determined by the Federal Statistical Office. The qualified rent index must be revised after four years.