If you don't record anything, you'll have no proof when it matters. If you charge based on consumption, the meter reading at arrival and the meter reading at departure are the only things that objectively show how much electricity a guest used. Without that record, you're left with only an estimate — and an estimate is exactly what disputes are made of.
The consequence is usually not dramatic, but it is inconvenient: a guest who disputes the amount on the final bill, accounting that doesn't add up, or a tax authority that asks during an audit how an amount was calculated without you being able to substantiate it. These aren't penalties that automatically follow, but practical problems you could have avoided with one simple habit: recording the readings, or having them recorded automatically.
What a meter reading precisely is, and why it matters so much
A meter reading is the number that the electricity meter displays at a given moment — comparable to the mileage on a car. The difference between the reading at arrival and the reading at departure is exactly the number of kilowatt-hours (kWh, the unit in which electricity consumption is measured) that was used during that period. Without those two snapshots, you can apply an average, but you cannot demonstrate what was actually consumed.
Suppose: a guest stays a week in your holiday home and uses the air conditioning extensively. At departure you record nothing and send, as is customary, a fixed amount. The guest thinks it's too high and asks for substantiation. Without readings, you have nothing to show. Had you recorded them, the conversation would be over in thirty seconds.
The practical consequences in brief
The first consequence is a dispute with the guest that you cannot settle with figures. Reviews on Airbnb or Booking regularly concern exactly this kind of ambiguity, and an unfairly felt electricity charge is a common reason for a poor review.
The second consequence is in the bookkeeping. A rental property with changing guests and no recorded meter readings has at the end of the year a series of amounts that cannot be traced back anywhere. For VAT and your own administration, that is inconvenient: you cannot show how an amount was built up, whereas that may be asked of you during an inspection.
The third consequence is more subtle: without readings, you yourself do not know either whether your current rate covers the actual costs. You only notice that you are making a loss on electricity when the annual statement from your energy supplier arrives, and by then it is too late to adjust per guest.
What is and is not established
Whether and how you may pass on energy costs to a guest differs per situation and per country, and that is something a lawyer or the competent supervisory authority can advise you on. What consistently comes up in practice: the more concrete your substantiation, the less room for discussion afterwards. A recorded meter reading, a photo of the meter, or a system that automatically keeps track of consumption, are each ways to have that substantiation without you having to search for it yourself. In the knowledge base you will find per situation what is at stake, without you needing an account for that.
How you keep the risk practically small
The simplest solution is to make the problem disappear instead of managing it: if consumption per guest is automatically measured and billed per kWh, there is no separate meter reading left to forget. The guest buys electricity, sees their own consumption live, and at a balance of zero the ordinary outlets switch off — the refrigerator group always stays on. There is simply nothing left that you have to manually record or remember.
If you prefer to work with a fixed amount or a manual meter reading, then make sure at least to set a fixed moment upon arrival and departure when you record the reading, for example with a photo that you keep. If you're unsure whether your current settlement method provides sufficient documentation, the FAQ answers the most common variants of it. And if you want to know where the information on this site comes from and how up-to-date it is, that is explained on the page how the information is created.
Recording a meter reading takes a minute, twice per stay. Not doing it costs you, in the worst case, an angry guest, accounting that doesn't add up, or a year in which you unknowingly operated at a loss. If you want to see in a few questions which approach suits your situation, take the free choice guide with a direct indication — which requires no account and no payment.