Invoice Numbering: Best Practices and Common Mistakes
Sequential, unique, no gaps: it sounds simple, but invoice numbering trips up more sellers than you would think. Here is how to get it right.
Invoice numbering seems trivial until you get it wrong. The Dutch tax authority requires sequential numbering, and "sequential" has a very specific meaning.
The rules
- Each invoice number must be unique: No duplicates, ever
- Numbers must be sequential: They should follow a logical order (1, 2, 3 or 2026-001, 2026-002, etc.)
- No gaps: If INV-005 exists, INV-004 must also exist (even if voided)
Common numbering formats
There's no required format, but these work well:
- YEAR-NUMBER: e.g., 2026-0001 (resets each year)
- PREFIX-NUMBER: e.g., MI-0001 (company prefix + sequential)
- Simple counter: e.g., 1, 2, 3 (works but less informative)
Mistakes to avoid
Using order numbers as invoice numbers. Order numbers come from your store. They can start anywhere, carry a prefix and skip numbers when a draft order is deleted. Generate your own invoice numbers and print the order number next to them.
Resetting mid-year. If you switch invoicing tools in June, don't restart at 001. Continue the sequence from where the previous tool left off.
One sequence for several stores. Sharing a single series between two stores leaves gaps in both of them. Give every store its own series, and keep credit notes in a series of their own.
How automatic invoicing handles this
With automatic invoicing, numbering is handled for you. Each invoice gets the next number in the sequence, with your preferred prefix and format. No gaps, no duplicates, no manual tracking.
