How to number invoices correctly
Invoice numbering isn't just a formality: it must be sequential and without gaps so tax authorities can verify that no issued invoice is missing. Here are the basic rules.
The main rule: sequencing
Each invoice must carry a higher number than the previous one, with no gaps or repeats. For example: 0001, 0002, 0003... If you cancel an invoice, keep the number (don't reuse it) and note that it was cancelled.
Can numbering restart each year
Yes, it's common and generally accepted practice to restart each calendar year, as long as it's clear which year each series belongs to (for example, by adding the year to the number: 2026-0001).
Using series or prefixes
You can use prefixes to distinguish invoice types or different business lines (for example, "INV-" or "A-"), as long as numbering is sequential within each series.
Common numbering mistakes
Skipping numbers when cancelling an invoice instead of recording the cancellation.
Mixing numbering from different years without distinguishing them.
Using duplicate numbers by mistake when invoicing manually.
Automatic, editable numbering
PreFactur automatically suggests the next invoice or quote number, but you can edit it freely if you need to match your own numbering.
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