ATCUD
What is ATCUD?
ATCUD (Código Único de Documento, or Unique Document Code) is a sequential identifier that Portugal requires on invoices and other fiscally relevant documents. It combines a validation code assigned to a document series by Portugal's tax authority with the document's own sequential number, joined by a hyphen, so every document a business issues can be traced back to an authorized series.
ATCUD has been mandatory since January 1, 2023, for companies issuing invoices, receipts, and other fiscally relevant documents in Portugal. It's one part of the country's wider fiscalization framework, alongside certified invoicing software and a QR code that must appear on the same document. Together, these requirements let the Autoridade Tributária e Aduaneira (AT), Portugal's tax and customs authority, confirm that a document belongs to a registered, sequential series rather than being created outside the reported record. For businesses selling into Portugal through or point of sale, ATCUD compliance sits alongside standard VAT invoicing obligations, not instead of them.
Key facts
- Full name: Código Único de Documento (Unique Document Code)
- Structure: a validation code for the document series, issued by AT, followed by a hyphen and the document's own sequential number
- Mandatory since: January 1, 2023, for fiscally relevant invoices and documents issued in Portugal
- Issued alongside: a QR code carrying the document's tax-relevant data, required on the same invoice or receipt
- Administered by: Autoridade Tributária e Aduaneira (AT), Portugal's tax and customs authority
Key requirements
- Register the invoice series: a business registers each document series it uses (POS, web store, backup system) with AT to obtain a validation code for that series.
- Generate the code per document: certified invoicing software attaches the validation code plus the document's own sequential number to every invoice or fiscally relevant document in that series.
- Display it on the document: ATCUD appears in the document header, or another designated area, together with the required QR code.
- Keep the sequence intact: document numbers within a series stay sequential, with no gaps and no back-dating.
- Support multiple series: a business issuing documents from more than one channel or system registers a separate series, and validation code, for each.
Who it applies to
ATCUD applies to any business issuing fiscally relevant documents in Portugal – invoices, receipts, and related records – whether the business is based in Portugal or selling into it as a foreign merchant. It's enforced through certified invoicing software: point-of-sale and billing systems used in Portugal must be certified by AT and generate ATCUD automatically as part of issuing a document, rather than leaving it to manual entry.
Why it matters
ATCUD gives AT a way to confirm that every invoice in circulation belongs to a registered, gap-free series, instead of being created after the fact to under-report sales. Combined with monthly SAF-T (PT) submissions, the code lets the tax authority cross-check what a business reports against what it actually issued, down to the individual document. For businesses, that means invoice records need to line up with both the ATCUD series and the SAF-T file at reconciliation, since a mismatch is exactly what AT audits are built to catch.
