Sam Edwards/Caia Image - stock.aIf the lease agreement stipulates that certain utility costs are to be allocated according to the number of occupants, the person-month model is frequently used in practice. This method ensures a fair distribution – especially when the number of occupants changes during the billing period, for example, due to someone moving in or out, or when there are different residents.
What are person-months and why are they used?
The term "person-month" refers to a calculated metric where the number of people is weighted by the number of days of use. This allows even partial months to be accurately accounted for – an advantage over simply counting people on a specific date.
The figure 30,42 is derived from the average number of days in a year (365 ÷ 12). Even in leap years or with atypical billing periods, this value remains the basis for calculation – because the per-person billing is based on a flat rate and not on precise consumption.
Example: If a tenant with two people moves in on June 10th and stays until December 31st, this equates to approximately 6,8 person-months per person. The sum of all individual values gives the total number of person-months in the building.
examples
The calculation of person-months can best be understood using these examples.
When is it permissible to bill per person?
The allocation of rooms based on the number of people is only permitted if it has been explicitly agreed upon in the rental agreement . This is common, for example, in the following cases:
- garbage fees
- General electricity
- House cleaning or other household-related services
The distribution of the following types of costs among persons is not permitted :
- Hot water costs: Billing may only be based on measured consumption (Heating Costs Ordinance § 5 para. 1)
- Heizkosten: also to be billed exclusively based on consumption
- Cold water: In most federal states, it must also be distributed according to consumption.
Only in exceptional cases – for example, if consumption-based metering is technically impossible or economically unreasonable – is a flat-rate charge permitted. Even then, however, the Heating Costs Ordinance stipulates distribution according to living space (§ 9a para. 2) , not according to the number of occupants.
Typical problems with billing per person
Whether it's additional visitors, unreported roommates, or conflicting information in the occupancy count: billing based on the number of people is often prone to errors and disputes in practice. For this reason, Brunata Minol generally recommends a consumption-based and accurately measured cost allocation – wherever it is legally required or technically feasible.
Conclusion: Person-months are useful, but legally limited.
Using person-months in utility billing is a practical method for fairly distributing costs when tenants change. However, it is only permissible if the rental agreement explicitly stipulates distribution based on the number of occupants – and it may not be used for heating or hot water costs . Consumption remains the only permissible criterion for these costs.
Author
Quelle: Handbuch der Wärmekostenabrechnung | Frank Peters Minol Messtechnik W. Lehmann GmbH & Co. KG, 2019
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