UBL Invoices Explained for Belgian Construction SMEs

What is a UBL invoice?

UBL (Universal Business Language) is a standard format for electronic business documents such as invoices, credit notes and purchase orders. In Belgium a UBL invoice is an XML file that contains all invoice data in a structured way that computer systems can read directly.

How does XML work?

An XML file is a plain‑text document where each piece of data is wrapped in a tag that describes what it is.

• In a PDF the amount “€10 176” appears somewhere on the page, but a computer cannot tell whether it is the total, the VAT amount or the invoice number.
• In a UBL invoice the same amount is stored as <PayableAmount currencyID="EUR">10176.00</PayableAmount>. The tag tells the system that this is the amount to be paid, in euros.

Main elements of a UBL invoice

A UBL invoice contains the same information as a paper invoice, but each item is placed in a defined section:

• Header – invoice number, issue date, due date, currency, document type (invoice or credit note)
• Supplier – company name, address, VAT number and bank details
• Customer – name, address and VAT number of the buyer
• Invoice lines – description, quantity, unit price, VAT rate and line total for each product or service
• VAT summary – totals per VAT rate (e.g., 6 %, 12 %, 21 %)
• Totals – subtotal (excl. VAT), total VAT, grand total (incl. VAT)
• Payment details – IBAN, structured communication, payment terms

Creating a UBL invoice

You should not create the XML file manually. A suitable invoicing solution should generate and validate the structured invoice from reviewed invoice data:

1. Create the invoice in the usual way (enter customer, line items, amounts, VAT).
2. The software produces a UBL XML file in the background.
3. The solution validates the document against the required profile before transmission.
4. For an in-scope Belgian B2B transaction, it sends the structured invoice through the configured route; emailing a PDF or XML attachment is not a substitute for that legal invoice.

The file is intended for machine processing; you never need to open or edit it yourself.

Which standard is used in Belgium?

Belgium uses Peppol BIS Billing as the reference profile for the B2B obligation, based on the European semantic standard EN 16931 and expressed using a structured syntax such as UBL. A file being XML or UBL-shaped does not by itself make it valid: the profile, business rules and receiver details must also pass validation.

UBL versus PDF

• PDF – designed for human readers. It looks good on screen and prints well, but extracting data requires OCR or manual entry, which can introduce errors.
• UBL – designed for computers. It is not human‑readable (unless you view the XML), but it can be processed automatically by accounting or ERP systems.

A readable view may accompany the structured invoice, but the recipient must retain and process the legally required structured document. The official Belgian FAQ explains that a PDF is not mandatory and does not replace the structured invoice.

Checklist for implementation

• Verify software support – Confirm that your invoicing solution can generate PEPPOL‑compatible UBL files.
• Test a sample invoice – Create a test invoice, export the UBL file and validate it with a PEPPOL validator (available from the Peppol Authority).
• Configure transmission – If you use the Peppol network, ensure your access point is correctly set up; otherwise prepare to attach the UBL file to e‑mail.
• Keep the structured original – Retain the structured invoice for the full period and preserve a legible view. FPS Finance states a ten-year retention period for invoices and VAT accounting documents.
• Review VAT details – Check that VAT numbers and rates are entered correctly; consult the Belgian tax administration for specific rules.

For more information on Belgium’s e‑invoicing obligations, visit the official portal Belgian e‑invoicing portal.
To verify how VAT rules apply to your specific situation, consult the Belgian tax administration VAT information for enterprises.