Glossary Term
BT-1

BT-1 Invoice Number

BT-1 is the unique identifier assigned by the seller to identify the invoice, required on every e-invoice.

Quick Facts

data type
Identifier
mandatory
true
cardinality
1..1

Definition

What is BT-1?

BT-1 (Invoice number) is a unique identifier assigned by the seller to identify a specific invoice. It's one of the most fundamental fields in any invoice and is mandatory in EN16931.

Requirements

  • Must be unique within the seller's invoice numbering series

  • Should follow a logical sequence

  • Many countries require sequential numbering without gaps

    • Best Practices

  • Include year prefix (2025-00001)

  • Use consistent format across all invoices

  • Keep records for audit purposes

    • Common Issues

  • Duplicate invoice numbers (rejected by some systems)

  • Gaps in sequence (problematic in some countries)

  • Format too long for some systems

    • XML Examples

    UBL (Peppol, XRechnung)

    <cbc:ID>INV-2025-00001</cbc:ID>

    CII (ZUGFeRD, Factur-X)

    <ram:ID>INV-2025-00001</ram:ID>