Raising the Rent on a Sitting Tenant (§558 BGB)

The standard route is the Mieterhöhung bis zur ortsüblichen Vergleichsmiete under §558 BGB. It is not a unilateral increase – it is a Zustimmungsverlangen, a request for consent.

Two waiting periods. The rent must have been unchanged for 15 months at the moment the increase takes effect, and you may not send a request until 12 months after the last one. Previous §559 (modernisation) and §560 (operating cost) adjustments do not reset this clock.

Two ceilings, and the lower one wins.

1. The ortsübliche Vergleichsmiete – rents agreed or changed for comparable flats in the last six years (§558(2)).
2. The Kappungsgrenze (§558(3)) – 20% over three years by default, reduced to 15% in designated areas. Bonn is a 15% municipality under the Mieterschutzverordnung NRW, currently until 28 February 2030.

Evidence. §558a requires you to justify the request with a Mietspiegel, a Mietdatenbank, a surveyor's opinion, or three comparable flats. Bonn has a qualifizierter Mietspiegel (§558d) – the 2026 edition, an index-based Fortschreibung using a factor of 1.044, took effect on 1 July 2026. A qualified Mietspiegel carries a statutory presumption of correctness, and where one exists you must cite its figures even if you argue from another source. Practically: use it, and expect to defend your Wohnwertmerkmale (size, fittings, location, energy quality) classification.

Procedure. Send it in Textform (email is fine), addressed to and signed on behalf of all landlords, naming all tenants. The tenant then has until the end of the second calendar month after receipt to agree; the higher rent runs from the month after that. No answer means no increase – you must sue for consent within a further three months (§558b(2)).

Silent tolerance is common but risky: repeated informal increases without this procedure are simply not owed.