Rent Increases in Practice: The 15% Cap & Bonn's Qualified Rent Index

When managing an existing tenancy, regular rent adjustments safeguard your real return against inflation. In German law, rent adjustments to comparable market rent (§558 BGB) are formal consent requests (Zustimmungsverlangen).

The Bonn Rules & Kappungsgrenze:

1. 15-Month Rule: The rent must remain unchanged for at least 15 months before an increase can take effect. You may submit the formal request after 12 months.
2. Kappungsgrenze: In designated tight housing markets under the NRW Mieterschutzverordnung, including Bonn, rent increases for existing tenancies are capped at 15% within a three-year period (down from the federal 20% default).
3. Qualifizierter Mietspiegel: Bonn publishes an official qualified rent index (qualifizierter Mietspiegel). It classifies flats by construction year, location, size, and fixtures (heating, flooring, modern bathroom). You must reference this official index in your request.

The Consent Procedure: The tenant has until the end of the second full calendar month following receipt of your request to review and provide written consent. If granted, the higher rent takes effect on the first day of the following month. If the tenant remains silent or refuses, you must file a court action for consent (Zustimmungsklage §558b BGB) within three months.