Rent increase - when is it (in)effective?

Before examining any formalities or the content of the request for a rent increase, it should be checked whether a rent increase is excluded per se due to a certain circumstance. Such a circumstance may be, for example

• It is a fixed-term tenancy agreement in accordance with Section 575 BGB. In this case, the rent can only be increased if this was provided for in the contract from the outset (graduated rent or index-linked rent).
• A rent increase was contractually excluded.
• The increase in rent is excluded due to a public subsidy for construction measures.

Then some formalities in the letter must be correct. These include in particular

1. The correct details of the landlord. If there are several landlords, they must all be named.
2. The correct details of the tenant(s) of the apartment.
3. Signature, facsimile or typed signature. A rent increase letter does not have to be signed by hand. However, some kind of (digital) signature or similar must prove the originality of the letter (text form in accordance with Section 126b BGB). The letterhead alone is not sufficient.
4. The total final amount of the new rent must be shown. The tenant must be able to understand how the new rent is calculated and how high the total amount of the new rent is that they are to agree to.
5. The initial rent (i.e. the current rent still to be paid) must be stated correctly.

In addition, it must be clear to the tenant that he is being asked to agree to the increase, i.e. that he has room for maneuver. Conversely, the impression must not be created that the tenant is being presented with a “fait accompli”.

Various deadlines apply for requesting a rent increase. According to the law, a rent increase may

1. can be claimed at the earliest one year after the last rent increase (so-called “blocking period”). “After the last rent increase” refers to the date on which the current rent first became due. It does not refer to the date of the claim (previous rent increase requests) or the date on which the rental agreement was concluded (if the rent was agreed in the rental agreement).
2. can only be increased if it has remained unchanged for 15 or more months at the time of the increased new rent (so-called “waiting period”).

It is important to note that the increase in the advance payment of operating costs (regulated in Section 560 (1) BGB) and also the increase due to modernization measures (regulated in Sections 559 et seq. BGB) are not to be taken into account when calculating the blocking and waiting period.

In addition, the law stipulates that the new rent must be paid from the start of the third calendar month after receipt of the rent increase request (provided that the tenant has agreed to the rent increase).
An example: If the tenant receives the request for an increase on June 13, they would have to pay the higher rent from September 1.

A core idea of the legal regulations on the subject of rent increases is that they must be limited. The law requires compliance with two different limits:

1. the so-called “local comparative rent” and
2. the so-called “cap limit”.

local comparative rent

The rent may only be increased up to the local comparative rent. This is calculated from the new and existing rents of comparable apartments over the last six years. As rents develop (generally upwards), the local comparative rent also develops. The comparative rent is determined according to five residential value characteristics: Type, size, fittings, condition and location (researchable for Berlin for a specific apartment via the so-called "Straßenverzeichnis Wohnlage") including the energy equipment and condition.

The so-called rent index ("Mietspiegel") (regulated in Sections 558c, 558d BGB and in the Mietspiegelverordnung) is a suitable means of determining the local comparative rent for an apartment. By law, a rent index is an overview of local comparative rents. Municipalities with more than 50,000 inhabitants are obliged to draw up a rent index. A rent index can either be drawn up by an authority responsible under state law or jointly by landlords' and tenants' interest groups. It is also possible for an interest group to draw up a rent index, which is then recognized by an interest group on the other side (e.g. an interest group of landlords) or the competent authority. Once created and recognized, the rent index and its amendments must then be published. However, the rent index is already valid before publication, namely from the respective survey date.

A rent index contains so-called rent index fields (or rent index lines). These fields/lines each contain so-called range values - a lower range value, an average value and an upper range value - which are based on the respective values of the above-mentioned housing value characteristics (type, size, fittings, condition and location).
Furthermore, the so-called “orientation guide for the range classification” is used for the exact calculation of the local comparative rent for a specific apartment: This contains numerous concrete so-called residential value-reducing features (e.g. “inadequate electrical installation”, “poor cut”) and so-called residential value-increasing features (e.g. “barrier-free apartment design” or “special and high-quality fittings” in the bathroom. The presence or absence of the residential value features ultimately influences where exactly the respective apartment is to be classified within the range of the respective rent index field (or rent index line). Many of the sometimes vague characteristics have therefore already passed through the courts.

A distinction must then be made between a so-called simple rent index (regulated in Section 558c BGB) and a so-called qualified rent index (regulated in Section 558d BGB). The latter must have been prepared in accordance with recognized scientific principles. The qualified rent index must be adjusted after two years (known as an update) and newly prepared after four years. While the simple rent index can only serve as an indication of the amount of the local comparative rent in a court case, the qualified rent index has a presumptive effect. This means that the other party (e.g. the landlord) must prove that the rent index does not reflect the local comparative rent. This means that if the rent index shows a certain rent range as customary in the area, tenants can rely on this range in court. The presumption of conformity refers to the respective range of the rent index - not to the mean value that may be stated. The Berlin rent index 2024 currently in force (as of 09.07.2025) is such a qualified rent index.

Cap limit

In some cases, landlords have not increased the rent for many years. This means that the local comparative rent may now be far higher than the rent currently payable. In such cases, the rent cap prevents particularly high jumps from the old rent to the new rent. According to the law, the rent may not increase by more than 20 % within three years. The key date for the calculation is the date from which the new rent is to be paid. The basis for the calculation is the so-called initial rent, i.e. the basic rent owed to date or - if contractually agreed - the inclusive rent owed to date.

The state governments are authorized to reduce this cap for certain areas to 15% for five years by statutory order (basis: Section 558 (3) sentence 2 BGB) if “the adequate supply of rental housing at reasonable conditions for the population in a municipality or part of a municipality is particularly at risk”. For example, a cap of 15 % applies to the following large cities (as at: 08.06.2025) Munich, Augsburg, Ingolstadt, Bamberg, Regensburg, Nuremberg, Stuttgart, Karlsruhe, Heidelberg, Freiburg, Potsdam, Bremen (excluding Bremerhaven), Frankfurt a.M., Wiesbaden, Darmstadt, Rostock, Greifswald, Berlin, Hamburg, Hanover, Braunschweig, Wolfsburg, Düsseldorf, Cologne, Bonn, Münster, Dresden, Leipzig, Kiel, Erfurt, Jena, Mainz, Landau, Ludwigshafen, Speyer, Potsdam (a complete overview of all areas is available at here).

The Berlin “Alliance for New Residential Construction and Affordable Housing” has also agreed on a cap of 11% (as of June 8, 2025). In addition to state-owned housing companies, this alliance also includes private rental companies such as Vonovia SE.

An important element of the legal logic of rent increases is that the tenant must be able to understand whether and, if so, why a rent increase is justified. The landlord therefore has a duty to explain and justify. The landlord can choose between four different means of justification to make it clear that the new rent does not exceed the local comparative rent:

1. Rent index ("Mietspiegel")
   If the landlord justifies the legality of the rent increase on the basis of the relevant rent index, he must refer to this specifically and also name the rent index field (or the rent index line) in which he has classified the apartment.


2. Rental database
   This means of justification is not relevant in practice, as rental databases are no longer compiled (only temporarily: City of Hanover).


3. A reasoned expert opinion from a publicly appointed and sworn expert
   An expert opinion costs the landlord money and is therefore rarely used. The expert must be publicly appointed and sworn, the expert opinion must be sent to the tenant with the request for a rent increase and it must be sufficiently understandable and justified for the tenant.


4. Charges for comparable apartments
   Finally, the landlord can also justify the rent increase by referring to at least three comparable apartments. The landlord must describe these alleged comparative apartments in such a way that the comparability is comprehensible. As a rule, at least the following information must be provided on the comparative apartments: Address, floor, QM price. The rental price of the cheapest of the comparative apartments stated is decisive.

Irrespective of a legally compliant justification, the tenant should have it checked whether the local comparative rent is the one stated by the landlord. If there is a qualified rent index (e.g. in Berlin, as of 09.07.2025), its values should be used in case of doubt. Regardless of the chosen justification method, the landlord is also obliged to provide the corresponding rent index field (or rent index line) of this rent index if a qualified rent index is available (Section 558a (3) BGB).