# What is EN 16931?

> EN 16931 is the European standard for the data model of an electronic invoice. Definition, what it contains and a worked example.

Updated 2026-11-06. Source: https://atta.sh/glossary/en-16931

EN 16931 is the European standard that defines the core data of an electronic invoice: seller, buyer, lines, taxes and totals, each with a numbered business term. Formats such as UBL and CII carry that model, so different systems read the same invoice.

## Example

Invoice 2026-114 has two lines: 10 chairs at 120.00 and delivery at 50.00, VAT 21% on both. Net is 1,250.00, VAT 262.50 and payable 1,512.50.

In the standard, the invoice number is BT-1, the purchase order reference is BT-13, and the VAT total is BT-110. A UBL file and a CII file hold the same business terms in different XML. Both validate against the same rules.

## In Atta

There is one EN 16931 model in the code, with amounts as decimal strings and never floats. Formats are rows in a table, each with its own reader and writer, and a format with no row is refused. Channels, such as Peppol, are separate from formats.

When an invoice is received, Atta links it to a purchase through BT-13, then BT-10, and shows it as that request's invoice row. When it sends one, the payload is stored exactly as it left. Keeping model, format and channel apart means a new country's format is a new row, not a rewrite.

## Why it exists

Before the standard, every country and vendor invented its own fields, and each pair of systems needed a mapping. A common semantic model means one mapping per system instead of one per pair. The numbered terms (BT-1, BT-13) are how validators and support teams point at the same field.

## Questions

### Does EN 16931 cover every country's rules?

It is the common core. Countries add their own extensions, called CIUS, on top.