The German rent index: how it is made and how to read it

What a rent index is for

The rent index is the main tool for working out a flat's local reference rent. That figure decides three things. First, rent increases: under Section 558 of the Civil Code a landlord may only ask you to agree to an increase up to the reference rent, and may justify the demand with the index (Section 558a BGB). Second, new leases: in areas with the rent brake the starting rent may be at most ten per cent above it. Third, benefits: job centres and social welfare offices use it to set reasonable housing costs.

Table indexes and regression indexes

In a table index a few features form the axes of a table, typically year built, floor area and location. Each flat falls into exactly one field, which gives a mean and a range. Berlin has 189 such lines across three tables for basic, average and good locations; Hamburg has one table with 90 fields for normal and good locations. Further features such as a balcony, a fitted kitchen or a modernised bathroom decide the position within the range.

In a regression index a statistical model has estimated from the surveyed rents how much each feature contributes. The result is a base rent, usually by floor area, and a list of premiums and deductions in euros or per cent. Munich, Frankfurt, Stuttgart, Leipzig, Nuremberg and Essen work this way; Dortmund combines a base table by year built with premiums in euros. Regression indexes are more precise but tedious without a calculator: you must know every feature and add or multiply correctly.

Simple or qualified

Of the 14 cities in our overview, 12 have a qualified index. Köln and Düsseldorf have simple indexes drawn up by associations. The difference matters legally: a qualified index is produced according to recognised scientific principles and recognised by the municipality or by both sides (Section 558d BGB). It carries the presumption that its figures reflect the reference rent, provided it was updated in time; whoever claims otherwise must prove it. A landlord must also quote a qualified index in his increase letter even if he justifies the increase differently. More on the qualified rent index page.

How to read your rent index

1. Check its scope. Does the index cover your flat? Detached and semi-detached houses, subsidised flats, furnished flats and very new buildings are usually excluded. Berlin's 2026 index, for example, covers flats completed by the end of 2024.
2. Look up the location. In the street directory, the location map or the city's online lookup.
3. Assign year and size. What counts is the year the flat was completed, not a later refurbishment, and the floor area under the Living Space Ordinance.
4. Rate the fittings. By the features the index lists; only what the landlord provided counts.
5. Compare the net cold rent. Indexes give net cold rents. If you pay an all-inclusive rent, take the service charges out.

For Berlin, Hamburg and Dortmund the rent check does these steps for you; for the other cities it takes you to the official tool and combines its result with your municipality's rules. The small tool above shows how the Berlin index picks a field: the 1965 flat of 62 m² in an average location lies in line 89.

How old may a rent index be?

A rent index should be adjusted to the market every two years (Section 558c(3) BGB). For a qualified index that is mandatory, and after four years it must be drawn up anew; the data reference date counts. If no current index exists, Section 558a(4) lets a landlord rely on an outdated one or that of a comparable municipality. Only a qualified index updated in time carries the legal presumption, though.