The invoice number: rules and examples
Every invoice number must be unique and sequential. It looks like a detail, but the Dutch tax office does check it, and tidy numbering keeps your bookkeeping clear.
The rules
- Unique: no number ever appears twice.
- Sequential: the numbers run upwards without unexplained gaps.
- Traceable: you must be able to account for the series in your records.
You are free to design the series yourself, as long as it stays unique and sequential.
Examples of a good series
- Per year:
2026-001,2026-002,2026-003. - Continuous:
0001,0002,0003. - With a client or project code, as long as the sequence numbers keep rising.
Common mistakes
- Skipping numbers, or restarting a series halfway through.
- Accidentally using the same number twice.
- No logic at all, so later you cannot explain which invoice is where.
Numbered automatically
In factuurmaken a logical next number is suggested, which you can adjust. With an account the numbering runs up automatically and reliably, even when you invoice a lot. What else belongs on the invoice is covered in What must a Dutch invoice contain.