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Allocation keys in Germany: living area or number of occupants?
Without an agreement, living area applies. When an occupancy key is valid, how a change works and how to redo the arithmetic.
The allocation key (Umlageschlüssel) decides which part of the building's total costs you carry. Two households in the same building with identical total costs can pay very different amounts depending on whether the split is by square metres, by occupants or by units. This guide explains which key applies when, how a change works, and how to check your share yourself. It covers residential tenancies in Germany and is not individual legal advice.
The statutory default
Under section 556a(1) BGB, operating costs are allocated by the proportion of living area unless the parties have agreed otherwise. Operating costs that depend on recorded consumption or recorded causation must be allocated by a standard that reflects the different consumption or causation.
Living area is therefore the statutory fallback. Where meters exist, consumption-based allocation takes precedence. For heating and hot water the Heating Costs Ordinance applies with its own rules.
Which living area counts
The Federal Court of Justice held that the actual living area is decisive for billing, not a different figure in the lease, and that the former ten-percent tolerance no longer applies (BGH, judgment of 30 May 2018 – VIII ZR 220/17).
In practice: if your lease says 68 m² but the flat measures 74 m², the actual area governs the allocation — to your disadvantage. The same works in your favour. So check which area appears in the statement and whether it fits your flat.
How much area is area
How much counts depends on the method of calculation. Under the Wohnflächenverordnung, balconies, loggias and terraces are normally counted at one quarter, in special cases up to one half. Cellars, laundry rooms and lofts do not count towards living area at all, and sloping ceilings reduce the countable area.
For your check a rough comparison usually suffices: does the stated area roughly match your flat? If you suspect a discrepancy of several square metres, a careful measurement is worthwhile — it affects every area-based item, not just one line.
The occupancy key
Allocation by number of occupants is possible where agreed. It is closer to cause for water, sewage and waste, because the volume depends on how many people live there. Disputes usually turn on two points: how many people were attributed to you, and how mid-year changes were handled.
A comprehensible statement gives the building's total occupancy and the number attributed to you, expressed as person-months where there were changes. If those figures are missing, your share cannot be verified — that is a legitimate objection.
Other possible keys
Also common are: the number of residential units, where every flat pays the same; the co-ownership share (Miteigentumsanteil), which comes from condominium law; recorded consumption for water and heat; the number of parking spaces for garage costs; and heated volume for certain heating elements.
The co-ownership share is delicate in a tenancy. It does not reflect living area and can produce considerable deviations. If your statement is derived from a condominium statement, check that the standard matches your lease.
Changing the key
Under section 556a(2) BGB the landlord may declare in text form that operating costs recorded by consumption will in future be allocated by consumption. The declaration is only permissible before the start of a billing period.
A change therefore does not operate retroactively. If a statement uses a new key mid-year without a valid declaration, that is a concrete objection. Ask for the date and wording of the declaration.
When the key changes every year
Some statements use different standards for the same item in successive years — area one year, occupants the next. That shifts the shares noticeably and is hard to follow without an explanation. Put two years' statements side by side and compare the key named for each line.
If something changed, ask for the basis: was a declaration under section 556a(2) BGB made, and when? Was the lease amended? Often it turns out that only the software or the manager changed — which is not a permissible reason for a different standard.
How to redo the arithmetic
You need four figures: the total costs of the item, the total units, your units, and the share shown. The calculation is: total costs ÷ total units × your units. If the result deviates, information is missing — usually a prior deduction or a pro-rata calculation.
Do this for each item separately. Often it works for most lines and fails for one; that line is your starting point.
The prior deduction for commercial units
In mixed-use buildings a prior deduction (Vorwegabzug) may be required where the commercial use causes significantly higher costs. The deduction is made before the allocation to the flats. A comprehensible statement gives the commercial area, the amount deducted and the remaining reference figure.
If no deduction is made although there is a restaurant or a laundry in the building, ask why. Not every commercial use requires one — a quiet office causes hardly any additional cost.
Vacancy
The share attributable to vacant flats is borne by the landlord (BGH, judgment of 31 May 2006 – VIII ZR 159/05). So make sure the total area includes the empty flats. A shrinking total area with no structural reason is a warning sign.
The billing unit
Before any key applies, it must be clear which building or group of buildings is being billed. If a whole estate is treated as one unit, the costs of one lift are spread across buildings without lifts. The billing unit follows from the lease or from a long-standing practice that was recognisable to you.
Compare the stated total area with the size of your building. If it does not fit, ask about the boundaries of the unit.
Read on and check your own bill
For the vacancy question, see vacancy costs. For consumption-based allocation of heat, see heating costs 70/30, and for writing an objection, objecting to a statement.
The free check redoes the arithmetic for every item, comparing total costs, key and your share, and flags the deviations.