Electricity refund

Hi, I was just about to start entering my energy costs (advance invoices) and the same thought occurred to me. I think it's best not to enter monthly advance invoices, but just enter your final bill. Of course, this means that my final bill doesn't always start from a new year. So that's also a problem.
I would like to hear the solution to this question above :-).

Rule of thumb for that professional percentage: 20% unless you can prove that it is higher because your professional space is more than 20% from the total living area or because of the nature of your activity (e.g. a car washer uses more water...).