Heating failure in January, mould in the bedroom, a permanent construction site outside the window: for significant defects, German rent reduces by operation of law – you don't "apply" for it.

"If the leased property has a defect at the time of handover that removes its suitability for contractual use, or if such a defect arises during the tenancy, the tenant is released from paying rent for the period in which suitability is removed. For the period during which suitability is reduced, the tenant need only pay an appropriately reduced rent."

— § 536 (1) BGB (translated)

The correct procedure

  1. Report the defect immediately (§ 536c BGB) – no notice, no reduction, and possibly liability.
  2. Preserve evidence: photos, temperature logs, witnesses.
  3. Set the percentage – calculated on the gross rent including service charges (Federal Court, XII ZR 225/03).
  4. Pay under reservation if the rate is uncertain – this avoids termination risk for arrears.

Benchmarks from case law

  • Total heating failure in winter: up to 100%
  • Mould in one living room: 10–20%
  • No hot water: around 10%
  • Severe construction noise: 10–25%
  • Elevator failure on upper floors: 5–10%

Caution: tenants who caused the defect themselves (poor ventilation) or knew of it at signing cannot reduce. Overshooting the rate can boomerang as payment default – seek advice in borderline cases.