E-invoicing in Belgium: The Complete Guide to the 2026 B2B Mandate
Belgium mandates Peppol-based B2B e-invoicing from January 2026. This guide covers the legal framework, accepted formats (UBL/Peppol BIS 3.0 and Factur-X), the Mercurius platform, and what Belgian companies must do to comply.
Belgium's B2B E-invoicing Mandate: What You Need to Know
Belgium is among the first EU countries to mandate structured electronic invoicing for B2B transactions between all VAT-registered companies. The law of 6 July 2023 (loi du 6 juillet 2023) and its implementing Royal Decree set January 1, 2026 as the mandatory date for B2B e-invoicing. Unlike some other EU countries, Belgium does not phase the mandate by company size — all Belgian VAT-registered entities must be capable of sending and receiving structured e-invoices from the same date.
Belgium's approach is notably network-centric: the Peppol network is the primary exchange infrastructure. Companies must connect to the Peppol network via an accredited access point (AP) rather than through a single centralised government platform. This network-first design aligns with Belgium's existing B2G infrastructure (Mercurius/Peppol) and enables seamless cross-border exchange with other Peppol-connected EU companies.
The mandate applies to invoices between Belgian VAT-registered entities for transactions subject to Belgian VAT. Small businesses (forfaitaire taxpayers and certain micro-enterprises) may benefit from a transitional period or simplified requirements — consult the SPF Finances/FOD Financiën guidance for the latest details on exemptions.
Common Mistakes and Rejection Causes
Belgian companies implementing e-invoicing for the first time encounter predictable issues. Here are the most common causes of invoice rejection or non-compliance:
Not registered on Peppol
To send and receive invoices via the Peppol network, your company must be registered with an accredited Peppol access point. Without a Peppol ID, your trading partners cannot discover your address on the Peppol SMP and cannot deliver invoices to you.
PDF-only invoices after the mandate date
After January 2026, PDF invoices (without embedded structured XML) are no longer legally accepted for B2B transactions between Belgian VAT-registered entities. A structured invoice in UBL/Peppol BIS 3.0 or Factur-X EN 16931 is required.
Wrong EN 16931 profile (insufficient data)
The Factur-X MINIMUM or BASIC WL profiles do not carry all mandatory business terms required by Belgian tax law. The EN 16931 (COMFORT) or EXTENDED profile must be used to include VAT numbers, payment details, and full line-item data.
Accepted Formats: UBL/Peppol BIS 3.0 and Factur-X
Belgium accepts any EN 16931-compliant format. In practice, this means UBL 2.1 via Peppol BIS Billing 3.0 (the dominant format for Peppol network delivery) or Factur-X at the EN 16931 (COMFORT) or EXTENDED profile. Both formats implement the same EN 16931 semantic data model, ensuring interoperability.
For companies already using Peppol for B2G procurement, the extension to B2B is straightforward: the same Peppol access point, the same UBL format, and the same four-corner model apply. For companies not yet on Peppol, selecting an accredited Belgian Peppol access point and ensuring your accounting software or ERP generates valid Peppol BIS 3.0 invoices are the two main implementation steps.
The Mercurius platform (operated by BOSA — Belgian public digital transformation service) continues as the B2G hub for public sector invoices. It accepts Peppol BIS 3.0 and is accessible via any accredited Peppol access point. Belgian companies already using Mercurius for B2G are automatically Peppol-connected for B2B as well.
How to Prepare for the 2026 Mandate
Belgian companies should start preparation immediately. The key steps are: (1) select an accredited Belgian Peppol access point (AP) — a list is available from OpenPeppol; (2) verify that your accounting software or ERP can generate valid Peppol BIS 3.0 UBL invoices; (3) test invoice delivery with major customers and suppliers before the mandate date; and (4) update your accounts payable process to accept and process incoming structured invoices.
The most common challenge is ERP readiness. Many Belgian SMEs use accounting software (Exact, Winbooks, BOB, Sage) that may require a software update or a module activation to generate EN 16931-compliant invoices. Contact your software vendor well before the mandate date to confirm compatibility.
ValidateFin can help you verify that your UBL/Peppol BIS 3.0 invoices are correctly structured before sending them to trading partners. Drop your XML invoice into the UBL validator and check EN 16931 compliance, Belgian VAT number format, and Peppol BIS 3.0 business rules — entirely in your browser, no file uploaded.
Validate Your Belgian E-invoices with ValidateFin
ValidateFin validates UBL/Peppol BIS 3.0 and Factur-X invoices against EN 16931 rules in your browser. Check Belgian VAT number format (BE0xxxxxxxxx), required fields, and Peppol BIS 3.0 business rules before sending to your Belgian trading partners.
Validate your invoice nowFrequently Asked Questions
When is Belgium's B2B e-invoicing mandatory?
January 1, 2026. The mandate applies to all invoices between Belgian VAT-registered companies. Both the obligation to send and to receive structured e-invoices (in EN 16931-compliant format via Peppol) apply from that date.
What format is required for Belgian B2B e-invoicing?
Any EN 16931-compliant format is accepted. In practice, this means UBL 2.1 via Peppol BIS Billing 3.0 (delivered through the Peppol network) or Factur-X at EN 16931 profile. Pure PDF invoices are no longer accepted after the mandate date.
Do all Belgian companies need to join Peppol?
To receive invoices via the Peppol network, yes — both sender and receiver must be registered on Peppol via an accredited access point. However, Factur-X invoices can also be exchanged directly via email or other channels. Contact your main suppliers and customers to agree on the delivery method.
What is the Mercurius platform?
Mercurius is Belgium's central B2G e-invoicing hub for public sector procurement. It is accessible via the Peppol network and accepts Peppol BIS Billing 3.0 invoices. Companies already connected to Mercurius for B2G are automatically Peppol-ready for B2B invoicing.
Is Factur-X accepted in Belgium?
Yes. Factur-X at EN 16931 (COMFORT) or EXTENDED profile is accepted. The MINIMUM and BASIC WL profiles are insufficient for Belgian compliance. The key requirement is that the invoice implements the EN 16931 semantic data model with all mandatory fields.
What Belgian VAT number format is required in e-invoices?
Belgian VAT numbers (BTW/TVA) follow the format BE + 10 digits (e.g. BE0123456789). The BE prefix is mandatory in EN 16931 invoices. The 10-digit format after BE includes the leading zero that Belgian tax authorities include in the national BTW number.
What happens if I send a PDF invoice after January 2026?
After the mandate date, PDF-only invoices are not legally compliant for B2B transactions between Belgian VAT-registered entities. Your trading partner is entitled to request a compliant structured invoice. The SPF Finances/FOD Financiën may impose penalties for non-compliance during enforcement phases.
How do I find an accredited Belgian Peppol access point?
OpenPeppol maintains a list of certified Peppol access points. Belgian-specific providers include Unifiedpost, Basware, Mercurius (for B2G), and international providers like Pagero, TrueCommerce, and Avalara. Your accounting software vendor may offer integrated access point services.
Does the mandate apply to invoices to foreign companies?
The mandate applies to invoices between Belgian VAT-registered entities for Belgian VAT-subject transactions. Invoices to foreign companies (outside Belgium) are not directly covered by the mandate, but cross-border Peppol invoicing is highly recommended for EU trading partners also implementing e-invoicing mandates.
Can ValidateFin validate Belgian e-invoices?
Yes. ValidateFin validates UBL/Peppol BIS 3.0 invoices against EN 16931 rules and checks Belgian VAT number format (BE0xxxxxxxxx) and Peppol BIS 3.0 business rules entirely in your browser. For Factur-X invoices, the Factur-X Viewer extracts and validates the embedded XML. No files are uploaded to any server.