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

A qualified rent index has been prepared according to recognized scientific principles and recognized by the municipality or by landlord and tenant stakeholders.

The qualified rent index is to be adjusted to market developments at intervals of two years. This may be based on a sample or on the development of the price index for the standard of living of all private households in Germany as determined by the Federal Statistical Office. After four years, the qualified representative list of rents is to be newly drawn up.