Invoice Series and Number: Numbering Rules (Without Mistakes)

Invoice numbering seems like a detail, but it’s one of the first things checked during an inspection. The basic rule: series with consecutive numbers, no gaps and no duplicates.

What the series is and what the number is

• The series — a prefix (e.g. FF, PF) that groups documents.
• The number — the consecutive value within the series (e.g. FF-0001, FF-0002).

Each document type usually has its own series: invoice, proforma, receipt, delivery note.

Numbering rules

• Consecutive — the numbers increase without skipping any.
• No gaps — you don’t leave “free” numbers.
• No duplicates — the same number doesn’t appear twice within the same series.
• Configured in advance — you set the series and the starting number before you start issuing.

Why it matters

Numbering with gaps or duplicates raises questions during a fiscal inspection and complicates reconciliation. That’s why automatic assignment of the next number (rather than manual) is the safest approach.

Correcting an invoice within a series

If an issued invoice is wrong, you don’t delete it and you don’t skip the number — you correct it through storno (an invoice with negative values). See the guide on the storno invoice.

How it works in facturifirma

In facturifirma you configure the series for each document type, with the starting number and the number of digits. When issuing, the app automatically assigns the next number in the series — so the numbering stays consecutive, without gaps or duplicates, with no manual effort.