The basis is always the gross warm rent
The Federal Court of Justice (Bundesgerichtshof) settled this in 2005: the basis for a reduction is the gross warm rent, not the net cold rent. For residential tenancies the ruling of 20 July 2005 applies (case VIII ZR 347/04); for commercial tenancies the court had already decided the same on 6 April 2005 (case XII ZR 225/03).
That means the net cold rent plus all advance payments or flat rates for operating costs. The reasoning: you pay for the flat as one package, so a defect diminishes the value of the whole package.
| Item | Example amount |
|---|---|
| Net cold rent (Nettokaltmiete) | 800,00 € |
| Operating costs advance (Betriebskosten) | 150,00 € |
| Heating costs advance (Heizkosten) | 50,00 € |
| Gross warm rent (basis of calculation) | 1.000,00 € |
In the example the difference between cold and warm rent comes to 40 € a month at a 20 % reduction. Over a year that is 480 €.
The formula
With a gross warm rent of 1,000 € and a reduction rate of 30 %, the reduction amounts to 300 €. You then owe 700 €.
Reduction amount = gross warm rent × reduction rate ÷ 100
Rent payable = gross warm rent − reduction amountCalculating by the day for shorter periods
If the defect does not last the whole month, the amount is prorated. The convention is to treat a month as 30 days.
Reduction amount = (gross warm rent ÷ 30) × days with the defect × rate ÷ 100
Example: 1,000 € warm rent, 12 days without heating, rate 80 %
= (1,000 ÷ 30) × 12 × 0.80
= 33.33 € × 12 × 0.80
= 320.00 €Note the start and end of the defect to the day. Those two dates are exactly what the size of your claim is built from later.
Several defects at once
A stubborn misconception lives here: that you may simply add up the rates of several defects. Courts do not. They ask, under § 536 Abs. 1 BGB, how badly the flat as a whole is impaired in its fitness for use, and they assess it as a whole. The rate awarded is therefore almost always below the sum of the individual values.
The sum of the table values is only a rough ceiling, not a result. That shows most clearly with defects that describe the same impairment at heart: a broken radiator and the flat being too cold because of it are counted once, not twice.
| Defect | Individual rate |
|---|---|
| Mould in one room | 10 % |
| Draughty windows in the same room | 8 % |
| Broken lift (4th floor) | 10 % |
| Sum of the individual values (guidance only) | 28 % |
| Realistic overall rate | below 28 % |
Our calculator reflects this: the highest single value counts in full, every further one only by half. That is still an estimate, but it no longer produces the 100 % results that plain addition reaches at four or five defects.
Effect on the annual operating cost statement
A rent reduction also affects the annual operating cost statement (Betriebskostenabrechnung). Because the advance payments are part of the reduced gross warm rent, any balance demanded for the period of the reduction must be cut accordingly.
So check your statement for whether the landlord took the reduction into account. If not, object in writing within the twelve-month objection period under § 556 Abs. 3 BGB.
How to find the right rate
- Use published rent reduction tables, which summarise court decisions in comparable cases
- Take duration, intensity and extent of the impairment into account — table values are ranges, not fixed figures
- When in doubt, estimate conservatively: too small a reduction costs money, too large a one can cost you the flat
- For larger amounts, have the rate checked by a tenants' association (Mieterverein) or a specialist lawyer
Every percentage in such tables comes from a decision on an individual case and is guidance only. No court is bound by them; what is assessed is always the case at hand.
Frequently asked questions
Is the reduction calculated from the cold or the warm rent?
From the gross warm rent, that is the net cold rent plus all advance payments for operating and heating costs. For residential tenancies the Federal Court of Justice decided this in its ruling of 20 July 2005 (case VIII ZR 347/04).
How do I calculate if the defect lasted only two weeks?
By the day: divide the gross warm rent by 30, multiply by the number of days with the defect and then by the reduction rate. At 1,000 € warm rent, 14 days and 20 %, that comes to 93.33 €.
May I add up the rates of several defects?
No, at least not as a result. Courts do not add; they assess as a whole how badly the flat is impaired overall. The sum of the individual values is only a rough ceiling; the rate awarded is regularly lower and can never exceed 100 %.
Does the reduction have to be reflected in the operating cost statement?
Yes. Because the advance payments are part of the reduced gross warm rent, any balance demanded for the period of the reduction must be reduced proportionally. Check the statement and object within twelve months of receiving it.
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Start now for freeMore guides
- Writing a defect notice (Mängelanzeige): template, required details and deadlines
- Paying rent under protest: the safe route to a rent reduction
- Retroactive rent reduction: when you can get money back
- When a rent reduction is excluded: 7 grounds
- The 10 most common mistakes in reducing rent
- Serving a defect notice: email, letter or registered post?
- The landlord is not responding to the defect notice: what you can do now
This article provides general information and does not constitute legal advice (Rechtsberatung). Despite careful research, no guarantee can be given for accuracy, completeness or timeliness. For specific legal questions, contact a tenants' association (Mieterverein) or a lawyer specialising in rental law.