On this page
- 01Software that reads your invoice without guessing
- 02An open OASIS standard with European rules
- 03What happens when you press send
- 04Every required detail has its field
- 05Invoicing Belgian customers from abroad
- 06Why a receiver rejects your invoice
- 07An accounting firm that stopped retyping
- 08Free in your package, work in your own software
Software that reads your invoice without guessing
With a UBL invoice nobody retypes what is on your invoice. The invoice number sits in an invoice number field, the VAT amount in a VAT field, the bank account in a payment field. Accounting software knows exactly what is what, where with a scanned PDF it has to guess.
Across Europe, UBL is the most common format for invoices that travel over the Peppol network. In Belgium, VAT-registered businesses have had to invoice each other this way since 1 January 2026; a PDF by email is no longer enough between them.
An open OASIS standard with European rules
UBL was developed by OASIS, an international consortium that builds open standards. Version 2.1 became an OASIS Standard on 4 November 2013 and was also published as ISO/IEC 19845:2015. EU Directive 2014/55 led to the European standard EN 16931, which sets the data an electronic invoice must be able to carry; Peppol turned that standard into a UBL format with its own rules, Peppol BIS Billing 3.0. That format is what most European invoicing software sends and receives.
What happens when you press send
You invoice as always in your software. On sending, the software creates a UBL file, checks every required field and sends it through your access point to your customer, whose Peppol address you can look up with the Peppol check. Their software validates the file again and gets it ready to book. A PDF version may travel inside the same file as an attachment for human readers, but the data in the fields is the invoice.
An invoice taken apart in five parts
A UBL invoice from a Belgian small business, shortened (sample data)
<Invoice xmlns="urn:oasis:names:specification:ubl:schema:xsd:Invoice-2">
<cbc:CustomizationID>urn:cen.eu:en16931:2017#compliant#urn:fdc:peppol.eu:2017:poacc:billing:3.0</cbc:CustomizationID>
<cbc:ID>2026-0412</cbc:ID>
<cbc:IssueDate>2026-10-22</cbc:IssueDate>
<cbc:DueDate>2026-11-21</cbc:DueDate>
<cac:AccountingSupplierParty> ...
<cbc:EndpointID schemeID="0208">0123456789</cbc:EndpointID>
<cac:PaymentMeans>
<cbc:PaymentID>+++202/6041/20066+++</cbc:PaymentID>
<cac:TaxTotal><cbc:TaxAmount currencyID="EUR">210.00</cbc:TaxAmount>
<cac:LegalMonetaryTotal><cbc:PayableAmount currencyID="EUR">1210.00</cbc:PayableAmount>
</Invoice>
- Which rulesStates that the invoice follows the European standard EN 16931 and the Peppol rules. Your customer's software checks against them.
- Number and datesInvoice number, issue date and due date: mandatory details, now as fields instead of text on a page.
- Who invoicesThe seller with their Peppol address: 0208 stands for the Belgian company number.
- How to payThe account and the structured payment reference, so the payment matches the invoice automatically.
- VAT and totalVAT amount and amount due as numbers. No more retyping errors at the customer.
A PDF is a picture of an invoice. A UBL file is the invoice itself, in fields software reads.
Every required detail has its field
| Required detail on an invoice | Where it sits in UBL | What software does with it |
|---|---|---|
| Invoice number and date | cbc:ID and cbc:IssueDate | Checks for duplicate numbers |
| Name, address and VAT number of seller and buyer | SupplierParty and CustomerParty | Matches the right supplier or customer |
| Peppol address | cbc:EndpointID with a scheme ID (0208 in Belgium) | Knows where replies go |
| Description, quantity, unit price | cac:InvoiceLine | Books each line to the right account |
| VAT rate and amount | cac:TaxTotal | Recalculates and books the VAT |
| Amount due and due date | LegalMonetaryTotal and DueDate | Schedules the payment |
| Account and payment reference | cac:PaymentMeans | Matches the payment to the invoice |
In Belgium the payment reference is often a structured communication, which lets the bank match the payment to the invoice at once.
Invoicing Belgian customers from abroad
If your company has no Belgian establishment, the Belgian mandate does not apply to you, but your Belgian customers' software is built to receive UBL over Peppol. Sending UBL is often the fastest way to get paid: the invoice lands in their books without a step in between. If your invoicing software already speaks Peppol in your own country, it speaks it in Belgium too. The guide to e-invoicing in Belgium covers who is in scope.
Why a receiver rejects your invoice
Every Peppol invoice is validated on sending and on receipt against the rules of Peppol BIS Billing 3.0. If one rule fails, the invoice does not arrive or comes back. The three errors we see most:
| Rule | What it requires | How it goes wrong |
|---|---|---|
| Buyer reference (PEPPOL-EN16931-R003) | A buyer reference or a purchase order number | Your package leaves the field empty because paper never required it |
| Totals add up (BR-CO-15) | Total with VAT equals total without VAT plus the VAT amount | Rounding per line and on the total differs by a cent |
| VAT category (BR-S-08 and related) | A separate subtotal per VAT rate | Lines at 6% and 21% share one subtotal |
A good package catches these before sending. If you invoice from your own software, run every invoice through a validator before it leaves; which software for Peppol lists providers that do it for you.
An accounting firm that stopped retyping
Take an accounting firm in Ghent that received hundreds of PDF invoices from clients each month until 2025, retyped or scanned by staff. Since 2026 invoices between businesses arrive as UBL. The accounting package reads supplier, amounts and VAT from the fields and proposes the booking; staff only check. The work shifts from retyping to reviewing.
Free in your package, work in your own software
Producing a UBL invoice costs nothing extra if your software can do it, and most European invoicing packages do. Which software for Peppol helps you choose. If you invoice from your own software, you build in the UBL export and connect a certified access point; Peppol invoicing software shows what that takes, and Peppol registration how to get on the network.
Converting a PDF rarely gives a valid file
Converting a PDF to UBL with an online converter often gives a file that fails validation. Let the software where the invoice is made produce the file.
What accountants and owners ask
What is the difference between a UBL invoice and a PDF?
A PDF is a picture of an invoice: people read it, software has to guess. UBL puts the same details in named fields, so the accounting package takes them over directly.
Is UBL the same as Peppol?
No. UBL is the file format, Peppol the network it travels over. Peppol uses UBL in its own variant, Peppol BIS Billing 3.0.
How do I open a UBL file?
Your accounting or invoicing software reads it in. To read it yourself, there is often a PDF attached inside the file, or free viewers show the content.
Is UBL used outside Belgium?
Yes. It is an international standard, and Peppol networks across Europe and beyond carry invoices in UBL. Some countries also accept other syntaxes under EN 16931.