# EN 16931 explained: the e-invoice standard behind Peppol

> EN 16931 is the European standard defining what an e-invoice contains. What it is, how BT codes and BR rules work, how Peppol builds on it, and the UK angle.

- Canonical URL: https://einvoices.uk/news/en-16931-explained
- Published: 20 October 2026 (2026-10-20)
- Last updated: 20 October 2026 (2026-10-20) (not updated since publication)
- Author: Floris Lindenaar, Editor, e-invoicing expert (https://einvoices.uk/authors/floris-lindenaar)
- Publisher: einvoices.uk (https://einvoices.uk)
- Type: Explainer
- Topics: Technical, Peppol, 2029 mandate, Compliance
- Language: en-GB (UK English); covers the United Kingdom

## Sources

- [Navigating the eInvoicing standard documentation – European Commission](https://ec.europa.eu/digital-building-blocks/sites/display/DIGITAL/Navigating%2Bthe%2BeInvoicing%2Bstandard%2Bdocumentation)
- [ConnectingEurope/eInvoicing-EN16931 validation artefacts](https://github.com/ConnectingEurope/eInvoicing-EN16931)
- [Peppol BIS Billing 3.0 (May 2026 release, version 3.0.21)](https://docs.peppol.eu/poacc/billing/3.0/bis/)
- [EN16931 model bound to UBL – Peppol BIS Billing 3.0 rules](https://docs.peppol.eu/poacc/billing/3.0/rules/ubl-tc434/)
- [Promoting electronic invoicing across UK businesses and the public sector: consultation response](https://www.gov.uk/government/consultations/promoting-electronic-invoicing-across-uk-businesses-and-the-public-sector/outcome/promoting-electronic-invoicing-across-uk-businesses-and-the-public-sector-consultation-response)
- [Tax update 2026: simplification, modernisation and fairness summary – GOV.UK](https://www.gov.uk/government/publications/summary-of-tax-update-2026-simplification-modernisation-and-fairness/tax-update-2026-simplification-modernisation-and-fairness-summary)

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**EN 16931** is the European standard for electronic invoicing. Its core part, EN 16931-1, defines a **semantic data model**: a numbered list of the information an e-invoice can carry (business terms such as BT-1 Invoice number), plus business rules (such as BR-CO-15) that say what is mandatory and how the numbers must add up. It is not a file format. The data is written in an XML syntax, usually UBL 2.1 or UN/CEFACT CII. Peppol BIS Billing 3.0, the format used on the network the UK has chosen, is built directly on it.

## Why it exists

EN 16931 was written by the European standards body CEN under the EU e-invoicing directive for public procurement (Directive 2014/55/EU). The European Commission says public bodies in scope must be able to receive and process e-invoices that follow it, in either of its two listed syntaxes. The aim was one shared definition of an invoice, so a buyer could process e-invoices from any supplier without one-off mappings.

## The parts

The Commission's guide lists the documents in the EN 16931 family:

| Document | What it covers |
|---|---|
| EN 16931-1:2017 | Semantic data model of the core elements of an electronic invoice |
| CEN/TS 16931-2:2017 | List of syntaxes that comply with EN 16931-1 |
| CEN/TS 16931-3-1 | Methodology for syntax bindings |
| CEN/TS 16931-3-2 | Syntax binding for UBL 2.1 invoice and credit note |
| CEN/TS 16931-3-3 | Syntax binding for UN/CEFACT XML Industry Invoice D16B |
| CEN/TS 16931-3-4 | Syntax binding for UN/EDIFACT INVOIC D16B |
| CEN/TR 16931-4 | Interoperability at the transmission level |
| CEN/TR 16931-5 | Using sector or country extensions with EN 16931-1 |
| CEN/TR 16931-6 | Results of testing the standard |

Only Part 1 is the European Norm (EN). The others are technical specifications (TS) and reports (TR). In the UK the standard is published by BSI as BS EN 16931.

## Business terms: the BT and BG codes

The semantic model gives every piece of information an ID:

- **BT** (business term): one item of data. BT-1 Invoice number, BT-2 Issue date, BT-31 Seller VAT identifier, BT-110 Invoice total VAT amount, BT-151 Invoiced item VAT category code.
- **BG** (business group): a group of terms. BG-4 Seller, BG-23 VAT breakdown, BG-25 Invoice line.

These IDs are the common language between syntaxes. BT-110 is `cac:TaxTotal/cbc:TaxAmount` in UBL and a different path in CII, but it means the same thing. When a validator says "BT-112", map it to your syntax using the binding. Peppol publishes the UBL paths for every term.

## Business rules: the BR codes

EN 16931 also defines business rules, published as Schematron by the European Commission's [eInvoicing-EN16931 project on GitHub](https://github.com/ConnectingEurope/eInvoicing-EN16931). They follow a naming pattern:

| Prefix | Covers | Example |
|---|---|---|
| BR-01 to BR-65 | Mandatory content and basic conditions | BR-16: "An Invoice shall have at least one Invoice line (BG-25)" |
| BR-CO | Conditions and calculations | BR-CO-15: "Invoice total amount with VAT (BT-112) = Invoice total amount without VAT (BT-109) + Invoice total VAT amount (BT-110)." |
| BR-S, BR-Z, BR-E, BR-AE, BR-O, BR-G, BR-IC… | Rules per VAT category | BR-E-10: exempt breakdowns need a reason |
| BR-CL | Code lists | BR-CL-18: "Invoice tax categories MUST be coded using UNCL5305 code list" |
| BR-DEC | Decimal places | BR-DEC-23: line net amount max 2 decimals |

The same rule IDs apply whatever the syntax. Each syntax also has its own structural rules: for UBL, `UBL-SR`, `UBL-CR` and `UBL-DT`.

See these in action in [common Peppol validation errors](https://einvoices.uk/news/common-peppol-validation-errors) and [BR-CO-15 explained](https://einvoices.uk/news/peppol-validation-error-br-co-15).

## Code lists

EN 16931 does not invent its own codes. It points to existing lists: ISO 4217 for currencies, ISO 3166 for countries, UN/CEFACT 5305 for VAT categories (S, Z, E, AE, O and others), UN/CEFACT 1001 for document types (380 invoice, 381 credit note), UN/ECE Recommendation 20 for units (HUR hours, C62 "one"), and the VATEX list for exemption reasons. Our [UK VAT category codes guide](https://einvoices.uk/news/uk-vat-category-codes-peppol) shows how UK VAT treatments map to these.

## CIUS: how Peppol builds on EN 16931

EN 16931 is deliberately broad. A **[CIUS](https://einvoices.uk/glossary#cius)** (core invoice usage specification) narrows it for a community. It can make optional fields mandatory, restrict code lists or add rules, but it cannot add new fields. A conforming CIUS invoice is always a valid EN 16931 invoice. Adding new fields needs an **extension**, the subject of CEN/TR 16931-5.

[Peppol BIS Billing 3.0](https://einvoices.uk/news/peppol-bis-billing-3-uk-guide) is a CIUS. Its specification identifier says so:

```text
urn:cen.eu:en16931:2017#compliant#urn:fdc:peppol.eu:2017:poacc:billing:3.0
```

On top of EN 16931, Peppol adds rules such as **PEPPOL-EN16931-R003** ("A buyer reference or purchase order reference MUST be provided."), **R010** (buyer electronic address required) and country-specific rules for several countries, but none for the UK. A Peppol invoice is validated against both the EN 16931 rules and the Peppol rules.

## EN 16931 in the UK today

**Confirmed:**

- For public procurement, "all bodies covered by the Public Procurement Act 2023 are required to accept e-invoices which comply with BS EN16931", according to the government's consultation response, which also notes that NHS Supply Chain requires its suppliers to e-invoice through Peppol. See [public sector e-invoicing regulations](https://einvoices.uk/news/public-sector-e-invoicing-regulations-2019).
- Mandatory e-invoicing for B2B and B2G VAT invoices starts on 1 April 2029.
- "The government has announced that the electronic procurement system Peppol will be the core interoperability network for e-invoicing in the UK" (Tax update 2026, 23 June 2026).

**Not yet confirmed:** the data standard for the 2029 mandate. The consultation response says the government "will work closely with stakeholders to review the risks and benefits of adopting an existing standard or designing a UK-specific standard", and its technical work "will encapsulate designing potential extensions to the standardised invoice to accommodate sector specific needs". Respondents strongly favoured existing standards "like EN16931". A UK CIUS of EN 16931 (or of Peppol BIS) would be a natural outcome, but that is **our reading, not a decision**. The roadmap is due at Budget 2026 on 28 October 2026.

## What it means for you

- **Finance teams:** you don't need to read the standard. You do need software that produces EN 16931-compliant invoices, and clean data to feed it. See the [readiness checklist](https://einvoices.uk/news/uk-e-invoicing-readiness-checklist).
- **Developers:** map your invoice model to EN 16931 business terms, not directly to one XML format. Then UBL, CII or a future UK specification is a binding change, not a rebuild. Start with [UBL vs CII](https://einvoices.uk/news/ubl-vs-cii-uk) and our [UK XML example](https://einvoices.uk/news/e-invoice-xml-example-uk).
- **Everyone:** watch the [timeline](https://einvoices.uk/timeline) for the UK specification.

## Frequently asked questions

### What is EN 16931?

EN 16931 is the European standard for electronic invoicing. Part 1 defines a semantic data model: the core information an e-invoice can contain, such as the invoice number, parties, lines, VAT breakdown and totals, plus the business rules that tie them together.

### Is EN 16931 a file format?

No. It defines the content, not the file. The content is expressed in an XML syntax, either UBL 2.1 or UN/CEFACT CII D16B.

### Does EN 16931 apply in the UK?

It is published in the UK as BS EN 16931. Public bodies covered by the Public Procurement Act 2023 must accept e-invoices that comply with it. Whether the 2029 B2B mandate will use it has not been confirmed.

### What is the relationship between EN 16931 and Peppol?

Peppol BIS Billing 3.0 is a specification built on EN 16931. Every Peppol invoice must meet the EN 16931 rules plus Peppol's own extra rules.

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How to cite: "EN 16931 explained: the e-invoice standard behind Peppol", einvoices.uk, 20 October 2026, https://einvoices.uk/news/en-16931-explained

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