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.
A series per year, per month or per day?
The law (article 35a of the Dutch VAT Act, the Wet op de omzetbelasting) asks for “a sequential number, in one or more series”. So several series are allowed. A series per year (2026-0001) is the most common, and a series per month (2026-09-0001) also occurs and is just as easy to account for.
A series that starts over every day (20260925-0001, 20260925-0002, the next day 0001 again) is, to the letter, also a separate series per day. It only weakens exactly what the rule is meant for: verifiability. Within a day you can still spot a missing number, but a day whose invoices are all missing shows up nowhere. If you choose this, the rest of your records (bank, sales ledger) has to make up for it. If all you want is to stop a client reading from the number how much you invoice, you can simply start higher: 2026-1001 is just as sequential as 2026-0001.
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.