The simple rent index represents an overview of the local comparative rent, insofar as the overview has been drawn up or recognised jointly by the municipality or by representatives of the interests of landlords and tenants. Mietspiegels can be drawn up for the area of a municipality or several municipalities or for parts of municipalities. Mietspiegels are to be adjusted to market developments at intervals of two years. Municipalities should draw up representative lists of rents if there is a need for them and if they can be drawn up at a reasonable cost. The representative lists of rents and their amendments are to be published. The Federal Government was empowered by law to issue regulations on the detailed content and procedure for drawing up and adjusting rent rolls by statutory order with the consent of the Bundesrat. On 16 December 2020, the Federal Cabinet adopted a draft law on the form of the rent index law. The aim of the reform is to improve the informative value of rent indices and to encourage more municipalities to draw up qualified rent indices. The rent index reform is on the agenda for first reading in the Bundestag on 16 April 2021.
A qualified rent index is a rent index that has been prepared according to recognised scientific principles and has been recognised by the municipality or by landlord and tenant stakeholders. It must be adjusted to market developments every two years. This may be based on a random 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 must be newly drawn up. If these regulations are complied with, it is presumed that the charges stated in the qualified representative list of rents reflect the comparable rent customary in the locality (§ 558d BGB).