SI-UBL vs Peppol BIS: E-Invoice Formats Explained for the Netherlands

Why Do E-Invoice Formats Matter?

When you send a paper invoice, the format is simple: a document with your company details, line items, and amounts. But electronic invoicing requires structured data that computers can read and process automatically. This is where standards and formats come in.

In the Netherlands, you will encounter several terms: SI-UBL, NLCIUS, Peppol BIS, UBL 2.1, and EN 16931. While these may seem confusing at first, they all work together to ensure that e-invoices can be exchanged seamlessly between businesses and government organisations.

This article breaks down each standard, explains how they relate to one another, and helps you understand which format to use in different situations.

EN 16931: The European Foundation

Everything starts with EN 16931, the European standard for electronic invoicing. This standard was developed by the European Committee for Standardisation (CEN) in response to EU Directive 2014/55/EU, which required all EU member states to accept e-invoices in public procurement.

EN 16931 defines a semantic data model for the core elements of an electronic invoice. It specifies what information an invoice must contain (such as seller details, buyer details, line items, VAT breakdown, and payment terms) but does not prescribe a specific technical format.

Instead, EN 16931 allows for multiple syntaxes (technical implementations). The two officially recognised syntaxes are:

• UBL 2.1 (Universal Business Language, maintained by OASIS)
• CII (Cross-Industry Invoice, maintained by UN/CEFACT)

Locally and across the Peppol network, UBL 2.1 is the dominant syntax.

UBL 2.1: The Technical Syntax

UBL 2.1 is an XML-based format that provides the technical structure for electronic documents, including invoices, credit notes, orders, and despatch advices. It defines the XML elements and attributes used to represent invoice data.

A UBL invoice is essentially an XML file with clearly defined tags such as:

• AccountingSupplierParty for the seller
• AccountingCustomerParty for the buyer
• InvoiceLine for each line item
• TaxTotal for VAT amounts
• PaymentMeans for payment details

UBL 2.1 is the raw technical format. On its own, it is very flexible but lacks the specific rules needed for a particular country or network. That is where profiles and localisations come in.

Peppol BIS Billing 3.0: The International Profile

Peppol BIS Billing 3.0 (Business Interoperability Specification) is a profile built on top of UBL 2.1 and fully compliant with EN 16931. It is the standard used across the international Peppol network for exchanging invoices and credit notes.

Peppol BIS adds specific business rules and validation requirements to ensure that invoices are complete, consistent, and processable. For example:

• Mandatory fields for cross-border transactions
• Rules for VAT calculation and reporting
• Requirements for document references and payment information
• Validation rules that invoices must pass before transmission

When you send an invoice via the Peppol network to a partner in another country (say Belgium, Germany, or Norway), Peppol BIS Billing 3.0 is the format you use. It ensures that the recipient can process your invoice regardless of their local system.

SI-UBL 2.0 (NLCIUS): The National Localisation

SI-UBL 2.0 is the national implementation of EN 16931, commonly known as NLCIUS (Netherlands Core Invoice Usage Specification). It is maintained by the local standardisation body and specifically tailored for the domestic market.

SI-UBL 2.0 builds on Peppol BIS Billing 3.0 and UBL 2.1 but adds country-specific requirements:

• KvK number: The Chamber of Commerce registration number is a mandatory identifier for businesses here
• BTW-id (VAT number): Specific formatting rules for local VAT identification numbers
• OIN (Overheids Identificatie Nummer): Used for government entities
• Local payment references: Support for domestic payment conventions
• Additional validation rules: Specific to national tax and business regulations

SI-UBL is the recommended format when invoicing public sector organisations and is widely used in domestic B2B transactions as well.

Which Format Should You Use?

The answer depends on who you are invoicing:

• Government (B2G): Use SI-UBL 2.0 (NLCIUS). This is the required format for public sector invoicing.
• Domestic businesses (B2B): SI-UBL 2.0 is recommended, but Peppol BIS 3.0 is also accepted since SI-UBL is a compatible extension.
• International partners (cross-border): Use Peppol BIS Billing 3.0, which is the internationally recognised format on the Peppol network.

The good news is that SI-UBL 2.0 and Peppol BIS 3.0 are highly compatible. An SI-UBL invoice will be understood by any Peppol participant worldwide, and a Peppol BIS invoice will be accepted by most domestic recipients.

How Peppol Box Handles Formats

With Peppol Box, you do not need to worry about manually choosing or converting between formats. Our platform:

• Automatically generates invoices in the correct format based on the recipient
• Validates all invoices against SI-UBL and Peppol BIS rules before sending
• Supports both domestic (SI-UBL) and international (Peppol BIS) invoicing
• Handles format conversion when receiving invoices from foreign partners
• Provides clear error messages if any validation rule is not met

Whatever accounting software you currently use, Peppol Box integrates smoothly through its API, CSV/XML export, or custom integrations -- ensuring your invoices are always in the right format without extra effort on your part. Your accountant can also use Flexina Sync to automatically retrieve your invoices from Peppol Box, free of charge.