A rent index gives you an overview of the rents of comparable apartments in your city or municipality. It contains clues as to

• whether a rent increase is justified,
• whether the rent level is permissible at the start of the tenancy if the apartment is located in an area in which the regulations of the so-called rent cap apply,
• whether the rent is generally reasonable.

The German Civil Code (BGB) and the Rent Index Ordinance differentiate between

• simple rent indexes
• and qualified rent indexes.

The simple rent index is an overview of the local comparative rent, which is calculated from the rents that have been newly set in the last 6 years on the occasion of a new letting or a rent increase. Rents from rent-controlled apartments are not included in the comparative rent.

In order for such an overview to actually be considered a rent index, it must be drawn up or recognized by the responsible authority, which is usually the local authority, or by the interest groups representing landlords and tenants.

A qualified rent index must also be prepared in such a way that it follows recognized scientific principles. In the event of a dispute, a qualified rent index has greater probative value than a simple one.

The rent index rent is shown per square meter. It varies depending on

• where an apartment is located and
• how large,
• old,
• energetically renovated
• or luxuriously furnished it is.

The fixtures and fittings of the apartment play a role, for example:

• Double-glazed windows,
• structural radiators or
• parquet flooring.

Cities or municipalities with more than 50,000 inhabitants are legally obliged to draw up a rent index.

Since July 1, 2022, all simple and qualified rent indexes have been available online free of charge.

Simple rent indexes should generally be adjusted to market developments and published every two years. In the case of qualified rent indices, an update is required every 2 years and a new one every 4 years.