In Portugal, electronic invoices and other tax documents must include the ATCUD code starting from January 2023. ATCUD is a unique identification number for documents comprised of 8 digits. There are two sections to it, separated by a dash (-):
- A code for service validation that the Portuguese tax authorities assign.
- Unique document code within the issued batch numbers which is generated by the software of the taxpayers themselves.
ATCUD shall not be confused with QR codes. QR codes exist separately and must be added only to invoices starting from January 2022. On the other hand, ATCUD code must be added both on invoices and other tax documents such as SAF-T files.