Invoice number

An invoice number is the unique number that an invoice carries - and it's ideal for identifying an invoice, both for the creditor and the debtor.

The invoice number is used in many contexts, including payment, where the debtor often adds the invoice number to the payment so that the creditor can easily register and settle the invoice.

It is a legal requirement that a creditor has an invoice number on their invoices - and that the numbering is consecutive.

Legal requirements for invoice numbers

What are the requirements for an invoice number?

There are basically not many requirements for an invoice number - just that it must always appear on the creditor's invoices, and that the number must be consecutive and thus in an unbroken series. In other words, there must be no missing numbers in the series (for example: 1, 2, 3, 5, 6, 7).

The creditor decides the format of the invoice numbers and can therefore use four digits (e.g. 0001) or just consecutive numbers (e.g. 1, 2, 3). The most important thing is to be consistent in your numbering.

The creditor can also choose where the numbering starts. Many start at 1, while others may start at 100 or 1000 - often to give the impression that more invoices have been sent than is actually the case.

An invoice number can contain letters (e.g. A1, A2, A3), but this is not very common.

Read more about invoice requirements here.

Remember the credit note

For example, when an invoice is canceled, a counter item must be created for the invoice and the debtor must be informed.

This is done with a credit note. The credit note must contain the original invoice number - and just like invoices, credit notes must also have a sequential number series. You can choose to continue in the same number series or create a separate series for credit notes.

Invoice with an accounting program

If you use a legal and registered accounting software, it will often be easy to comply with invoice numbering requirements - as the software automatically assigns the next number in line.

This article aims to give you insight into invoice numbers in general and to make you aware that you can use different formats - as long as you decide from the start which format you want to use. If you need a template for an invoice, you can find an invoice template here.