The deadlines for different types of invoices are determined by the provisions to the Bookkeeping Act.
The act itself states that the invoice must be sent as soon as possible, and not later than one month after the delivery. The exceptions are:
TYPE OF GOODS/SERVICES
Fifteen working days into the next month.
Running services, e.g. auditor services, legal services, etc.
One month after the ordinary VAT deadline. E.g. auditor services rendered in January and February must be invoiced by 31 March.
Electricity, telephone bills and other types of invoices based on real consumption
Not later than one year and before 31 December
Invoiced in accordance with the contract, unless the progress deviates significantly from the plans.
VAT eligible businesses must invoice the same year as the delivery takes place.
Pre-invoicing including VAT is normally not allowed. However, there are exceptions for licences, rent and similar services. Such services may be pre-invoiced (and pre-paid) within the actual year.