Requirements for invoice numbers

Invoice numbers need to be unique, chronological and sequential. This requirement is set by Belgian legislation. You can decide on the starting number, but the order must remain consistent and no numbers should be skipped. Spaces are not allowed, but punctuation marks like dashes are fine.

Assigning your first invoice number in Teamleader One

When creating your first invoice in Teamleader One, you can choose the format of the invoice number at the time of invoice creation. You have a few options: in the prefix field, you might use Invoice or INV, followed by a dash (-) or a slash (/). The starting number will automatically increase with each new invoice.

Have you already sent invoices this year? Then use the next number as your starting point. Is this your first invoice of the year? Feel free to choose a starting number, such as 1, 001 or 125.

Example

If you choose Invoice as the prefix and 1 as the starting number, your invoice number will look like this:

Adjusting invoice numbers

Once you have finalised your first invoice, you cannot easily change the invoice numbers, as they need to remain unique, chronological and sequential. At the beginning of a new fiscal year, you can adjust your numbering, but afterwards, the series must again be unique and sequential.

Soon, you will be able to set fiscal years in Teamleader One. Until then, you can start using 2025 as a prefix.

If you do wish to change the number of a finalised invoice, you can do so by reopening the invoice. You can read more about this here.