Invoice numbering rules in the EU: sequences, series and gaps

Article 226(2) of the VAT Directive asks for one thing from an invoice number: that it be sequential, based on one or more series, and uniquely identify the invoice. Everything else — prefixes, yearly resets, how many series you run — is a choice, as long as the result is a sequence a tax inspector can follow without gaps they cannot explain.

Sequential, unique, in a series

A series is any run of numbers with its own counter: 2026-0001, 2026-0002 or INV-000123, INV-000124. You may run several series in parallel — one per company, per branch, per document type, per year — but within a series the numbers must follow one another. Reusing a number, or numbering out of chronological order within a series, is the error inspectors look for first.

When you need more than one series

• Credit notes and corrective invoices: keep them out of the invoice sequence, in their own series. Spain requires a specific series for rectifying invoices.
• Several establishments or invoicing systems issuing in parallel, so that two systems never race for the same number.
• Self-billed invoices issued on your behalf by a customer, which must be distinguishable from your own.
• A new year, if you prefer counters that restart: 2027-0001 after 2026-0412 is a new series, not a gap.

Gaps

A gap is not illegal in itself but it has to be explainable: a voided draft that never became an invoice is not a gap, because a number is only consumed when the invoice is actually issued. The safe design is to allocate the number at the moment of issue, atomically, so drafts never hold numbers and two invoices can never receive the same one.

Changing software or importing history

When you move to a new tool mid-year, continue the series you were using: if the last invoice was C010, the next must be C011. Importing the historical invoices with their original numbers, and letting the new system adopt the pattern and continue the count, keeps one unbroken sequence in your records.

How EUFactura does it

Numbers are allocated inside the issue transaction — never for drafts — from a series you configure per company: prefix, separator, padding, and whether the counter resets each year. Imported invoices keep their own numbers and the series continues from the highest one; credit notes get their own series.